Doctor of Philosophy

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"Ph.D." redirects here. For other uses, see Ph.D. (disambiguation).

Doctor of Philosophy, abbreviated PhD (also Ph.D.), for the Latin philosophiæ doctor, meaning "teacher of philosophy", or alternatively, DPhil, Dr. phil. or similar, for the equivalent doctor philosophiæ, is an advanced academic degree awarded by universities. In many English-speaking countries, the PhD is the highest degree one can earn ^[1] and applies to graduates in a wide array of disciplines in the sciences and humanities. The PhD or equivalent has become a requirement for a career as a university professor or researcher in most fields.

The detailed requirements for award of a PhD degree vary throughout the world. In some countries (the US, Canada, Denmark, for example), most universities require coursework in addition to research for PhD degrees. In many other countries (such as the UK) there is generally no such condition. It is not uncommon, however, for individual universities or departments to specify additional requirements for students not already in possession of a master's degree.

In countries requiring coursework, there is usually a prescribed minimum amount of study — typically two to three years full time, or a set number of credit hours — which must take place before submission of a thesis. This requirement is usually waived for those submitting a portfolio of peer-reviewed published work. The candidate may also be required to successfully complete a certain number of additional, advanced courses relevant to his or her area of specialization.

A candidate must submit a thesis or dissertation consisting of a suitable body of original academic research, which is in principle worthy of publication in a peer-refereed context.^[2] In many countries a candidate must defend this work before a panel of expert examiners appointed by the university; in other countries, the dissertation is examined by a panel of expert examiners who stipulate whether the dissertation is in principle passable and the issues that need to be addressed before the dissertation can be passed.

Universities in the non–English-speaking world have begun adopting similar standards to those of the Anglophone PhD degree for their research doctorates (see, for example, the Bologna Process).^[3]

The doctorate was extended to philosophy in the European universities in the Middle Ages which generally placed all academic disciplines outside the professional fields of theology, medicine and law under the broad heading of "philosophy" (or "natural philosophy" when referring to science). According to Wellington, Bathmaker, Hunt, McCullough and Sikes (2005), the first Doctor of Philosophy degree was awarded in Paris in 1150, but not until the early nineteenth century, following the practice in Germany, did the degree acquire its modern status as an advanced research degree. As Wellington et al. explain, prior to the nineteenth century professional doctoral degrees could only be awarded in theology (ThD), law (JD), or medicine (MD). In 1861, Yale University adopted the German practice (first introduced in the 19^th century at the Berlin University) of granting the degree to younger students who had completed a prescribed course of graduate study and successfully defended a thesis/dissertation containing original research in science or in the humanities.^[4]

From the United States the degree spread to Canada in 1900, and then to the United Kingdom in 1917.^[5] This displaced the existing Doctor of Philosophy degree in some universities; for instance, the DPhil (higher doctorate in the faculty of philosophy) at the University of St Andrews was discontinued and replaced with the PhD (research doctorate). Oxford retained the DPhil abbreviation for their research degrees. Some newer UK universities, for example Buckingham (est. 1976), Sussex (est. 1961), and, until a few years ago, York (est. 1963), chose to adopt the DPhil, as did some universities in New Zealand.

Contents [hide] 1 Doctor of Philosophy degrees across the globe 1.1 Australia and New Zealand 1.1.1 Admission 1.1.2 Funding 1.1.3 Requirements for Completion 1.2 Argentina 1.2.1 Admission 1.2.2 Funding 1.2.3 Requirements for completion 1.3 Canada 1.3.1 Admission 1.3.2 Funding 1.3.3 Requirements for completion 1.4 France 1.4.1 Admission 1.4.2 Funding 1.5 Germany 1.5.1 Admission 1.5.2 History 1.6 Norway 1.7 Spain 1.8 United Kingdom 1.8.1 Admission 1.8.2 Funding 1.8.3 Completion 1.8.4 Other doctorates 1.9 United States 1.9.1 Overview 1.9.2 Admission 1.9.3 Master's degree "in passing" 1.9.4 Time 1.9.5 Funding 1.9.6 Ph.D. candidacy 2 Models of supervision 3 See also 4 Notes 5 References 6 External links

Ph.D. degrees are awarded under different circumstances and with different requirements in many different countries.

Admission to a Ph.D. program within Australia and New Zealand requires the prospective student to have completed a bachelor's degree with an honours component or a higher degree, such as a post graduate master's degree by research or a master's degree by course work.

In most disciplines, honours require an extra year of study including a large research component in addition to coursework; however, in some disciplines such as engineering, law and pharmacy, honours are automatically awarded to high achievers of the normal four-year program. To obtain a Ph.D. position, students must usually gain first class honours, but may sometimes be admitted with upper second class honours. Alternatively, a student who fails to achieve first or second class Honours may apply for a research masters course (usually 12–18 months) and upgrade to a Ph.D. program after the first year, pending sufficient improvement.

[edit] Funding

In both Australia and New Zealand, Ph.D. students are sometimes offered a scholarship to study for their Ph.D. degree. The most common of these in Australia is the government-funded Australian Postgraduate Award (APA), which provides a living stipend to students of approximately AU$ 20,000 a year (tax free). Most universities in both countries also offer a similar scholarship that matches the APA amount, but are funded by the university. In recent years, with the tightening of research funding in Australia, these scholarships have become increasingly hard to obtain. Due to a continual increase to living costs, many Ph.D. students are forced to live under the poverty line,^[6]. In addition to the more common APA and University scholarships, Australian and New Zealand students also have other sources of funding in their Ph.D. degree. These could include, but are not limited to, scholarships offered by schools, research centres and commercial enterprise. For the latter, the amount is determined between the university and the organisation, but is quite often set at the APA (Industry) rate, roughly AU$7,000 more than the usual APA rate. Australian and New Zealand students are often also able to tutor undergraduate classes and do guest lectures (much like a teaching assistant in the USA) to generate income. An Australian or New Zealand Ph.D. scholarship is paid for a duration of 3 years, while a 6 month extension is usually possible upon citing delays out of the control of the student.

Australian-citizen and other eligible Ph.D. and Research Masters students in Australia are not charged course fees as these are paid for by the Australian Government under the Research Training Scheme. International students and Coursework Masters students must pay course fees, unless they receive a scholarship to cover them. In order to attract top international doctoral students, the New Zealand government reduced international doctoral fees to the domestic fee level in 2006.

Completion requirements vary by school, however all require completion of an original research thesis or dissertation that makes a significant new contribution to the field. Most Australian and New Zealand PhD programmes do not have a required coursework component, or a formal oral defense as part of the doctoral examination (largely due to distances that would need to be travelled by the overseas examiners). The PhD thesis is sent to three external examiners, experts in the field of research, who have not been involved in the work. Examiners are nominated by the candidate's University (often by the Head of Department or Research Office), and their identities are often not officially revealed to the candidate until the examination is complete.

In the Latin American docta, the admission to a Ph.D. program at an Argentine University requires the full completion of a Master's degree or a Licentiate's degree. Non-Argentinian Master's titles are generally accepted into a Ph.D. program when the degree comes from a recognized university.

While a significant portion of postgraduate students finance their tuition and living costs with teaching or research work at private and state-run institutions, international institutions, such as the Fullbright Program and the Organization of American States (OAS), have been known to grant full scholarships for tuition with apportions for housing.^[7]

Upon completion of at least two years' research and course work as a graduate student, a candidate must demonstrate truthful and original contributions to his or her specific field of knowledge within a frame of academic excellence.^[8] The doctoral candidate's work should be presented in a dissertation or thesis prepared under the supervision of a tutor or director, and reviewed by a Doctoral Committee. This Committee should be composed of examiners external to the program, and at least one of them should also be external to the institution. The academic degree of Doctor, respective to the correspondent field of science that the candidate has contributed with original and rigorous research, is received after a successful defense of the candidate’s dissertation.^[9]

Admission to a Ph.D. program at a Canadian university may require completion of a Master's degree in a related field, with sufficiently high grades and proven research ability. In some cases, a student may progress directly from an Honours Bachelor's degree to a Ph.D. program. The student usually submits an application package including a research proposal, letters of reference, transcripts, and in some cases, a sample of the student's writing. A common criterion for prospective Ph.D students is the comprehensive or qualifying examination, a process that often commences in the second year of a graduate program. Generally, successful completion of the qualifying exam permits continuance in the graduate program. Formats for this examination include oral examination by the student's faculty committee (or a separate qualifying committee), or written tests designed to demonstrate the student's knowledge in a specialized area (see below).

At English-speaking universities, a student may also be required to demonstrate English language abilities, usually by achieving an acceptable score on a standard examination (e.g., Test of English as a Foreign Language (TOEFL)). Depending on the field, the student may also be required to demonstrate ability in one or more additional languages. A prospective student applying to French-speaking universities may also have to demonstrate some English language ability.

[edit] Funding

While some students work outside the university (or at student jobs within the university), in some programs students are advised (or must agree) not to devote more than ten hours per week to activities (i.e., employment) outside of their studies, particularly if they have been given funding. For large and prestigious scholarships, such as those from NSERC, this is an absolute requirement.

At some Canadian universities, most Ph.D. students receive an award equivalent to the tuition amount for the first four years (this is sometimes called a tuition deferral or tuition waiver). Other sources of funding include teaching assistantships and research assistantships; experience as a teaching assistant is encouraged but not requisite in many programs. Some programs may require all Ph.D. candidates to teach, which may be done under the supervision of their supervisor or regular faculty.

Besides these sources of funding, there are also various competitive scholarships, bursaries, and awards available, such as those offered by the federal government via NSERC, CIHR, or SSHRC.

[edit] Requirements for completion

In general, the first two years of study are devoted to completion of coursework and the comprehensive examinations. At this stage, the student is known as a "Ph.D. student." It is usually expected that the student will have completed most of his or her required coursework by the end of this stage. Furthermore, it is usually required that by the end of eighteen to thirty-six months after the first registration, the student will have successfully completed the comprehensive exams.

Upon successful completion of the comprehensive exams, the student becomes known as a "Ph.D. candidate." From this stage on, the bulk of the student's time will be devoted to his or her own research, culminating in the completion of a Ph.D. thesis or dissertation. The final requirement is an oral defense of the thesis, which is open to the public in some, but not all, universities.

At most Canadian universities, the time needed to complete a Ph.D. degree typically ranges from four to six years^{[citation needed]}. It is, however, not uncommon for students to be unable to complete all the requirements within six years, particularly given that funding packages often support students for only two to four years; many departments will allow program extensions at the discretion of the thesis supervisor and/or department chair. Alternate arrangements exist whereby a student is allowed to let their registration in the program lapse at the end of six years and re-register once the thesis is completed in draft form. The general rule is that graduate students are obligated to pay tuition until the initial thesis submission has been received by the thesis office. In other words, if a Ph.D. student defers or delays the initial submission of their thesis they remain obligated to pay fees until such time that the thesis has been received in good standing.

Students who want to earn the PhD degree must complete a Master's degree program which lasts for 2 years after graduation with a Bachelor's degree (5 years in total).

The candidate must find a funding and a formal advisor with an habilitation (Directeur de thèse) throughout the doctoral program.

In France, the Masters program is divided into two branches, a "master professionnel" which orientates the students towards the working world. On the other hand, a Master of Research (Master-recherche) orientates the students towards research. The PhD admission is adopted by a graduate school (in French, "école doctorale"), a PhD Student has to follow some courses offered by the graduate school while continuing his/her research at laboratory. His/her research may be carried out in a laboratory, at a university, or in a company. In the last case, the company hires the student as an engineer and the student is supervised by both the company's tutor and a labs' professor. The validation of the PhD degree requires generally 3 to 4 years after the Master degree. Consequently, the Ph.D degree is considered in France as a "Bac +8" diploma ."Bac" stands for Baccalauréat which is the French High-school diploma.

The financing of Ph.D studies comes mainly from funds for research of French Ministry of Research. These grants often depend of the results and the student's file. However, the student can apply for funds from a company who can host him/her at its premise (as in the case where Ph.D students do their research in a company). Many other resources come from some regional/city projects, some associations, etc.

[edit] Germany

See also: Education in Germany

[edit] Admission

In Germany an above-average degree (Master, Diplom, Magister or Staatsexamen) is usually required to gain admission to a doctoral program. The degree should usually be in a related field. The candidate must also find a tenured professor or Privatdozent to serve as the formal advisor and supervisor (Betreuer) of the dissertation throughout the doctoral program. This supervisor is informally termed "Doktorvater".

Doctoral programs in Germany generally take one to four years to complete (usually three, up to five in Engineering), strongly depending on the subject. Since there are usually no formal classes to attend, and the doctoral candidate mainly conducts independent research under the tutelage of a single professor, a good deal of doctoral candidates work as teaching or research assistants, and are paid a reasonably competitive salary. This is a considerable difference from the situation in many other countries (such as the U. S.), where doctoral candidates are often referred to as Ph.D. "students". For German doctoral candidates, this rather inaccurate term should be avoided, because they do not take formal courses, but are often considered a full member of staff.

However, external funding by research organisations and foundations is also common. Furthermore, many universities have established research-intensive Graduiertenkollegs, which are colleges / graduate schools that provide funding for doctoral theses.

[edit] History

In early university history the Doctorate was awarded as a first degree. It has since evolved into a research degree.

In German-speaking countries, most Eastern European countries, the former Soviet Union, most parts of Africa, Asia, and many Spanish-speaking countries the corresponding degree is simply called "doctor" (Doktor), and is distinguished by subject area with a Latin suffix (e.g. "Dr. med." for doctor medicinae, "Dr. rer. nat" for doctor rerum naturalium — Doctor of Natural Science, "Dr. phil." for doctor philosophiae, "Dr. iur." for doctor iuris, etc.).

In the former Soviet Union, the Doctor of Sciences is the higher of two sequential post-graduate degrees, with Candidate of Sciences (Russian - кандидат наук) being universally accepted as the equivalent of the PhD, while the Doctorate is a (Full) Professors' or Academicians' separate and subsequent degree, indicating that the holder is a distinguished, honoured, and outstanding member of the scientific community. It is rarely awarded to those younger than late middle age or lacking in achievement and is a symbol of success in an academic career.

[edit] Norway

Main article: Dr. philos. (Norwegian degree)

Norway was one of the first countries to introduce the Doctor of Philosophy degree, inspired by the German university system. The degree doctor philosophiae, abbreviated dr. philos., was first awarded in 1847.^[10] The degree was used for all other fields than theology, law and medicine, which had separate degrees: doctor theologiae, doctor juris and doctor medicinae. In the late 20th century new degrees were created in the fields of natural sciences, humanities and social sciences, but it was still possible to obtain the dr. philos. degree in any field. As the dr. philos. degree was one of the four original doctoral degrees and much older than the specific degrees in natural sciences, humanities and social sciences, it was considered more prestigious by some. Both the dr. philos. degree and the other degrees required four years of high-level scientific research which significantly contributed to new knowledge of its field. Most people who started at a doctoral degree had already studied for six or seven years and obtained a Candidate degree (six years) or a Magister degree (seven years).

Following a reform in 2003, all the traditional degrees except dr. philos. were abolished, and replaced by a new doctor of philosophy degree, spelled philosophiae doctor and abbreviated ph.d. The scientific standard of the ph.d. degree is lower, as it in most cases only requires three years of research.

The traditional degree dr. philos., equivalent of four years of scientific research, is still awarded to those who qualify for such a degree without being admitted to an organized doctoral programme.

[edit] Spain

Doctor Degrees are regulated by Royal Decree (R.D. 778/1998), ^[11] Real Decreto (in Spanish). They are granted by the University on behalf of the King, and its Diploma has the force of a public document. The Ministry of Science keeps a National Registry of Theses called TESEO ^[12]. According to the National Institute of Statistics (INE), less than 5% of M.Sc. degree holders are admitted to Ph.D. programs, and less than 10% of 1st year Ph.D. students are finally granted a Doctor title.^[13]

All doctoral programs are of research nature. A minimum of 5 years of study are required, divided into 2 stages:

1) A 3-year long period of studies, which concludes with a public dissertation presented to a panel of 3 Professors. If the projects receives approval from the university, he/she will receive a "Diploma de Estudios Avanzados" (part qualified doctor).

2) A 2-year (or longer) period of research. Extensions may be requested for up to 10 years. The student must write his thesis presenting a new discovery or original contribution to Science. If approved by his "thesis director", the study will be presented to a panel of 5 distinguished scholars. Any Doctor attending the public presentations is allowed to challenge the candidate with questions on his research. If approved, he will receive the doctorate. Four marks can be granted (Unsatisfactory, Pass, "Cum laude", and "Summa cum laude"). Those Doctors granted their degree "Summa Cum Laude" are allowed to apply for an "Extraordinary Award".

A Doctor Degree is required in order to apply to a teaching position at the University.

The social standing of Doctors in Spain is evidenced by the fact that only Ph.D. holders, Grandees and Dukes can take seat and cover their heads in the presence of the King^[14]. All Doctor Degree holders are reciprocally recognized as equivalent in Germany and Spain ("Bonn Agreement of November 14 1994")^[15].

A University of Oxford DPhil in full academic dress.

[edit] Admission

Universities admit applicants to Ph.D. programmes on case by case basis; depending on the university, admission is typically conditional on the prospective student having successfully completed an undergraduate degree with at least upper second-class honours, or a postgraduate master's degree, but requirements can vary. Oxford, for example, claims "The one essential condition of being accepted...is evidence of previous academic excellence, and of future potential."^[16] Commonly, students are first accepted on to an MPhil programme and may transfer to PhD regulations upon satisfactory progress. This is typically done after one or two years, and the research work done can potentially count towards the PhD degree. If a student fails to make satisfactory progress, he or she may be offered the opportunity to write up and submit for an MPhil degree.

In addition, Ph.D. students from countries outside the EU/EFTA area are required to comply with the Academic Technology Approval Scheme (ATAS), which involves undergoing a security clearance process with the Foreign Office for certain courses in medicine, mathematics and many natural, engineering and material sciences.^[17][18] This requirement was introduced in 2007 due to concerns about terrorism and weapons proliferation.^[18]

[edit] Funding

In the United Kingdom, funding for Ph.D. students is sometimes provided by government-funded Research Councils or the European Social Fund, usually in the form of a tax-free bursary which consists of tuition fees together with a stipend of around GBP 12,940 per year for three years (rising to £14,940 per year in London),^[19] whether or not the degree continues for longer. Research Council funding is sometimes 'earmarked' for a particular department or research group, who then allocate it to a chosen student, although in doing so they are generally expected to abide by the usual minimum entry requirements (typically a first degree with upper second class honours, although successful completion of a postgraduate master's degree is usually counted as raising the class of the first degree by one division for these purposes). However, the availability of funding in many disciplines (especially humanities, social studies, and pure science^{[citation needed]} subjects) means that in practice only those with the best research proposals, references and backgrounds are likely to be awarded a studentship. The ESRC (Economic and Social Science Research Council) explicitly state that a 2.1 minimum (or 2.2 plus additional masters degree) is required - no additional marks are given for students with a first class honours or a distinction at masters level.

Since 2002, there has been a move by research councils to fund interdisciplinary doctoral training centres such as MOAC^[20] which concentrate on communication between traditional disciplines and an emphasis on transferable skills in addition to research training.

Many students who are not in receipt of external funding may choose to undertake the degree part time, thus reducing the tuition fees, as well as creating free time in which to earn money for subsistence.

Students may also take part in tutoring, work as research assistants, or (occasionally) deliver lectures, at a rate of typically £25–30 per hour, either to supplement existing low income or as a sole means of funding.^[21]

[edit] Completion

There is usually a preliminary assessment to remain in the programme, and the thesis is submitted at the end of a 3-4 year program. Because students in the UK specialize in a subject at a much earlier stage in their education, the timeline of 4 years to complete a PhD program is equivalent with the North American PhD. History undergraduates at Oxbridge for example refer to themselves as "historians" (their undergraduate exams similar in breadth and depth to PhD-level coursework in North America), while American undergrads are "history majors." Thus, someone with an American undergrad degree pursuing a PhD in the UK typically is required to complete up to two years (MPhil) of coursework before embarking on a PhD programme. At top UK universities the two-year MPhil is "comparable to the first two years of the PhD programme in the best US universities."^[22] The PhD timeline in the humanities, therefore, depending on one's starting point, can typically be 2+4, or six years, especially for students coming from countries where less early specialization takes place. These periods are usually extended pro rata for part-time students. With special dispensation, the final date for the thesis can be extended for up to four additional years, for a total of seven, but this is rare.^{[citation needed]} Since the early 1990s, the UK funding councils have adopted a policy of penalising departments where large proportions of students fail to submit their theses in four years after achieving PhD-student status (or pro rata equivalent) by reducing the number of funded places in subsequent years.^[23]

[edit] Other doctorates

In the United Kingdom Ph.D. degrees are distinct from other doctorates, most notably the higher doctorates such as D.Litt. (Doctor of Letters) or D.Sc. (Doctor of Science), which are granted on the recommendation of a committee of examiners on the basis of a substantial portfolio of submitted (and usually published) research.

Recent years have seen the introduction of professional doctorates, most notably in the fields of engineering (Eng.D.), education (Ed.D.), clinical psychology (D.Clin.Psych.), public administration (D.P.A.), business administration (D.B.A.), and music (D.M.A.). These typically have a more formal taught component consisting of smaller research projects, as well as a 40,000-60,000 word thesis component, which collectively is equivalent to that of a Ph.D. degree.

[edit] United States

[edit] Overview

Further information: Doctorate#United States

In the United States, the Ph.D. degree is the highest academic degree awarded by universities in most fields of study. The Ph.D. degree is often misunderstood to be synonymous with the term doctorate. While the Ph.D. degree is the most common doctorate, the term doctorate can refer to any number of doctoral degrees in the United States. The U.S. Department of Education and the National Science Foundation recognize numerous doctoral degrees as "equivalent", and do not discriminate between them. In law, for example, these entities recognize the degree of Doctor of Juridical Science (J.S.D.) as the equivalent to the Ph.D.

American students typically undergo a series of three phases in the course of their work toward the Ph.D. degree. The first phase consists of coursework in the student's field of study and requires one to three years to complete. This often is followed by a preliminary, a comprehensive examination, or a series of cumulative examinations where the emphasis is on breadth rather than depth of knowledge. The student is often later required to pass oral and written examinations in the field of specialization within the discipline, and here, depth is emphasized. Some Ph.D. programs require the candidate to successfully complete requirements in pedagogy (taking courses on higher level teaching and teaching undergraduate courses) or applied science (e.g., clinical practica and predoctoral clinical internship in Ph.D. programs in clinical or counseling psychology).

Another two to four years are usually required for the composition of a substantial and original contribution to human knowledge in the form of a written dissertation, which in the social sciences and humanities typically ranges from 50 to 450 pages in length. In many cases, depending on the discipline, a dissertation consists of (i) a comprehensive literature review, (ii) an outline of methodology, and (iii) several chapters of scientific, social, historical, philosophical, or literary analysis. Typically, upon completion, the candidate undergoes an oral examination, sometimes public, by his or her supervisory committee with expertise in the given discipline.

As the Ph.D. degree is often a preliminary step toward a career as a professor, throughout the whole period of study and dissertation research the student may be required or at least offered the opportunity, depending on the university and degree, to teach undergraduate or sometimes graduate courses in relevant subjects.

The Ph.D. can also be awarded as a religious-exempt degree, if having a religious modifier, like Ph.D. in Religion or Ph.D. in Metaphysics.

[edit] Admission

There are 282 universities in the United States that award the Ph.D. degree, and those universities vary widely in their criteria for admission, as well as the rigor of their academic programs.^[24] Typically, Ph.D. programs require applicants to have a Bachelor's degree in a relevant field (and, in rare cases, a master's degree), reasonably high grades, several letters of recommendation, relevant academic coursework, a cogent statement of interest in the field of study, and satisfactory performance on a graduate-level exam specified by the respective program (e.g., GRE, GMAT).^[25][26] Specific admissions criteria differ substantially according to university admissions policies and fields of study; some programs in well-regarded research universities may admit less than five percent of applicants and require an exceptional performance on the GRE along with near-perfect grades, strong support in letters of recommendation, substantial research experience, and academically sophisticated samples of their writing.

[edit] Master's degree "in passing"

As applicants to many Ph.D. programs are not required to have master's degrees, many programs award a Master of Arts or Master of Science degree "in passing" or "in course" based on the graduate work done in the course of achieving the Ph.D. Students who receive such master's degrees are usually required to complete a certain amount of coursework and a master's thesis. Depending on the specific program, masters-in-passing degrees can be either mandatory or optional. Not all Ph.D. students choose to complete the additional requirements necessary for the M.A. or M.S. if such requirements are not mandated by their programs. Those students will simply obtain the Ph.D. degree at the end of their graduate study.

[edit] Time

Depending on the specific field of study, completion of a Ph.D. program usually takes four to eight years of study after the Bachelor's Degree; those students who begin a Ph.D. program with a master's degree may complete their Ph.D. degree a year or two sooner.^[27] As Ph.D. programs typically lack the formal structure of undergraduate education, there are significant individual differences in the time taken to complete the degree. Many U.S. universities have set a ten-year limit for students in Ph.D. programs, or refuse to consider graduate credit older than ten years as counting towards a Ph.D. degree. Similarly, students may be required to re-take the comprehensive exam if they do not defend their dissertations within five years of taking it. Overall, 57% of students who begin a Ph.D. program in the US will complete their degree within ten years, approximately 30% will drop out or be dismissed, and the remaining 13% of students will continue on past ten years.^[28]

[edit] Funding

Doctoral students are usually discouraged from engaging in external employment during the course of their graduate training. As a result, Ph.D. students at U.S. universities typically receive a tuition waiver and some form of annual stipend. The source and amount of funding varies from field to field and university to university. Many U.S. graduate students work as teaching assistants or research assistants while they are doctoral students. Graduate schools increasingly^{[citation needed]} encourage their students to seek outside funding; many are supported by fellowships they obtain for themselves or by their advisers' research grants from government agencies such as the National Science Foundation and the National Institutes of Health. Many Ivy League and other well-endowed universities provide funding for the entire duration of the degree program (if it is short) or for most of it.

[edit] Ph.D. candidacy

A Ph.D. Candidate (sometimes called Candidate of Philosophy) is a postgraduate student at the doctoral level who has successfully satisfied the requirements for doctoral studies, except for the final thesis or dissertation. As such, a Ph.D. Candidate is sometimes called an "ABD" (All But Dissertation or All But Defended). Although a minor distinction in postgraduate study, achieving Ph.D Candidacy is not without benefit. For example, Ph.D. Candidate status may coincide with an increase in the student's monthly stipend and may make the student eligible for additional employment opportunities.

Some programs also include a Master of Philosophy degree as part of the Ph.D. program.^[29] The M.Phil., in those universities that offer it, is usually awarded after the appropriate M.A. or M.S. (as above) is awarded, and the degree candidate has completed all further requirements for the Ph.D. degree (which may include additional language requirements, course credits, teaching experiences, and comprehensive exams) aside from the writing and defense of the dissertation itself. This formalizes the "all but dissertation" (ABD) status used informally by some students, and represents that the student has achieved a higher level of scholarship than the M.A./M.S. would indicate - as such, the M.Phil. is sometimes a helpful credential for those applying for teaching or research posts while completing their dissertation work for the Ph.D. degree itself. ^[30]

Ph.D. Candidate is not to be confused with Candidate of Sciences, an academic degree that has been used in certain countries in place of PhD.

[edit] Models of supervision

At some universities, there may be training for those wishing to supervise Ph.D. studies. There is now a lot of literature published for academics who wish to do this, such as Delamont, Atkinson and Parry (1997). Indeed, Dinham and Scott (2001) have argued that the worldwide growth in research students has been matched by increase in a number of what they term "how-to" texts for both students and supervisors, citing examples such as Pugh and Phillips (1987). These authors report empirical data on the benefits that Ph.D. students may gain if they publish their work, and note that Ph.D. students are more likely to do this with adequate encouragement from their supervisors.

Wisker (2005) has noticed how research into this field has distinguished between two models of supervision: The technical-rationality model of supervision, emphasising technique; The negotiated order model, being less mechanistic and emphasising fluid and dynamic change in the Ph.D. process. These two models were first distinguished by Acker, Hill and Black (1994; cited in Wisker, 2005). Considerable literature exists on the expectations that supervisors may have of their students (Phillips & Pugh, 1987) and the expectations that students may have of their supervisors (Phillips & Pugh, 1987; Wilkinson, 2005) in the course of Ph.D. supervision. Similar expectations are implied by the Quality Assurance Agency's Code for Supervision (Quality Assurance Agency, 1999; cited in Wilkinson, 2005).

Current sea level rise

This article is about the current and future rise in sea level associated with global warming. For sea level changes in Earth's history, see Sea level - changes in geologic time.

Sea level measurements from 23 long tide gauge records in geologically stable environments show a rise of around 200 millimetres (8 inches) per century, or 2 mm/year.

Changes in sea level since the end of the last glacial episode

Current sea level rise has occurred at a mean rate of 1.8 mm per year for the past century,^[1][2] and more recently at rates estimated near 2.8 ± 0.4^[3] to 3.1 ± 0.7^[4] mm per year (1993-2003). Current sea level rise is due partly to global warming,^[5] which will increase sea level over the coming century and longer periods^[6][7]. Increasing temperatures result in sea level rise by the thermal expansion of water and through the addition of water to the oceans from the melting of continental ice sheets. Thermal expansion, which is well-quantified, is currently the primary contributor to sea level rise and is expected to be the primary contributor over the course of the next century. Glacial contributions to sea-level rise are less important,^[8] and are more difficult to predict and quantify.^[8] Values for predicted sea level rise over the course of the next century typically range from 90 to 880 mm, with a central value of 480 mm. Based on an analog to the deglaciation of North America at 9,000 years before present, some scientists predict sea level rise of 1.3 metres in the next century.^[9][10] However, models of glacial flow in the smaller present-day ice sheets show that a probable maximum value for sea level rise in the next century is 800 millimetres, based on limitations on how quickly ice can flow below the equilibrium line altitude and to the sea.^[11]

Contents [hide] 1 Overview of sea-level change 1.1 Local and eustatic sea level 1.2 Short term and periodic changes 1.3 Longer term changes 1.3.1 Glaciers and ice caps 2 Past changes in sea level 2.1 The sedimentary record 2.2 Estimates 2.3 U. S. Tide Gauge Measurements 2.4 Amsterdam Sea Level Measurements 2.5 Australian Sea Level Change 3 Future sea level rise 3.1 Intergovernmental Panel on Climate Change results 3.1.1 Uncertainties and criticisms regarding IPCC results 3.2 Glacier contribution 4 Greenland contribution 5 Antarctic contribution 6 Effects of snowline and permafrost 6.1 Polar ice 7 Effects of sea level rise 7.1 Island nations 8 Satellite sea level measurement 9 See also 10 Notes 11 References 12 External links

[edit] Overview of sea-level change

[edit] Local and eustatic sea level

Water cycles between ocean, atmosphere, and glaciers.

Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes. Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. Atmospheric pressure, ocean currents and local ocean temperature changes also can affect LMSL.

“Eustatic” change (as opposed to local change) results in an alteration to the global sea levels, such as changes in the volume of water in the world oceans or changes in the volume of an ocean basin.

[edit] Short term and periodic changes

There are many factors which can produce short-term (a few minutes to 18.6 year ) changes in sea level.

Short-term (periodic) causes	Time scale (P = period)	Vertical effect
Periodic sea level changes
Diurnal and semidiurnal astronomical tides	12–24 h P	0.2–10+ m
Long-period tides
Rotational variations (Chandler wobble)	14 month P
Lunar Node astronomical tides	18.613 year
Meteorological and oceanographic fluctuations
Atmospheric pressure	Hours to months	−0.7 to 1.3 m
Winds (storm surges)	1–5 days	Up to 5 m
Evaporation and precipitation (may also follow long-term pattern)	Days to weeks
Ocean surface topography (changes in water density and currents)	Days to weeks	Up to 1 m
El Niño/southern oscillation	6 mo every 5–10 yr	Up to 0.6 m
Seasonal variations
Seasonal water balance among oceans (Atlantic, Pacific, Indian)
Seasonal variations in slope of water surface
River runoff/floods	2 months	1 m
Seasonal water density changes (temperature and salinity)	6 months	0.2 m
Seiches
Seiches (standing waves)	Minutes to hours	Up to 2 m
Earthquakes
Tsunamis (generate catastrophic long-period waves)	Hours	Up to 10 m
Abrupt change in land level	Minutes	Up to 10 m

[edit] Longer term changes

Various factors affect the volume or mass of the ocean, leading to long-term changes in eustatic sea level. The two primary influences are temperature (because the volume of water depends on temperature), and the mass of water locked up on land and sea as fresh water in rivers, lakes, glaciers, polar ice caps, and sea ice. Over much longer geological timescales, changes in the shape of the oceanic basins and in land/sea distribution will affect sea level.

Observational and modelling studies of mass loss from glaciers and ice caps indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century.

[edit] Glaciers and ice caps

Each year about 8 mm (0.3 inch) of water from the entire surface of the oceans falls into the Antarctica and Greenland ice sheets as snowfall. If no ice returned to the oceans, sea level would drop 8 mm every year. To a first approximation, the same amount of water appeared to return to the ocean in icebergs and from ice melting at the edges. Scientists previously had estimated which is greater, ice going in or coming out, called the mass balance, important because it causes changes in global sea level. High-precision gravimetry from satellites in low-noise flight has since determined Greenland is losing millions of tons per year, in accordance with loss estimates from ground measurement.^{[citation needed]} Some estimates range up to 240 km^3 per year in recent years.^[12]

Ice shelves float on the surface of the sea and, if they melt, to first order they do not change sea level. Likewise, the melting of the northern polar ice cap which is composed of floating pack ice would not significantly contribute to rising sea levels. Because they are fresh, however, their melting would cause a very small increase in sea levels, so small that it is generally neglected. It can however be argued that if ice shelves melt it is a precursor to the melting of ice sheets on Greenland and Antarctica^{[citation needed]}.

• Scientists previously lacked knowledge of changes in terrestrial storage of water. Surveying of water retention by soil absorption and by reservoirs outright ("impoundment") at just under the volume of Lake Superior agreed with a dam-building peak in the 1930s-1970s timespan. Such impoundment masked tens of millimetres of sea level rise in that span. ( Impact of Artificial Reservoir Water Impoundment on Global Sea Level, http://www.sciencemag.org/cgi/content/full/320/5873/212?rss=1 B. F. Chao,* Y. H. Wu, Y. S. Li).
• If small glaciers and polar ice caps on the margins of Greenland and the Antarctic Peninsula melt, the projected rise in sea level will be around 0.5 m. Melting of the Greenland ice sheet would produce 7.2 m of sea-level rise, and melting of the Antarctic ice sheet would produce 61.1 m of sea level rise.^[13] The collapse of the grounded interior reservoir of the West Antarctic Ice Sheet would raise sea level by 5-6 m.^[14]
• The snowline altitude is the altitude of the lowest elevation interval in which minimum annual snow cover exceeds 50%. This ranges from about 5,500 metres above sea-level at the equator down to sea level at about 70° N&S latitude, depending on regional temperature amelioration effects. Permafrost then appears at sea level and extends deeper below sea level polewards.
• As most of the Greenland and Antarctic ice sheets lie above the snowline and/or base of the permafrost zone, they cannot melt in a timeframe much less than several millennia; therefore it is likely that they will not, through melting, contribute significantly to sea level rise in the coming century. They can, however, do so through acceleration in flow and enhanced iceberg calving.
• Climate changes during the 20th century are estimated from modelling studies to have led to contributions of between –0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and runoff).
• Estimates suggest that Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long-term adjustment to the end of the last ice age.

The current rise in sea level observed from tide gauges, of about 1.8 mm/yr, is within the estimate range from the combination of factors above^[15] but active research continues in this field. The terrestrial storage term, thought to be highly uncertain, is no longer positive, and shown to be quite large.

Since 1992 a number of satellites have been recording the change in sea level;^[16][17] they display an acceleration in the rate of sea level change, but they have not been operating for long enough to work out whether this is a real signal, or just an artefact of short-term variation.

[edit] Past changes in sea level

Changes in sea level during the last 9,000 years

[edit] The sedimentary record

For generations, geologists have been trying to explain the obvious cyclicity of sedimentary deposits observed everywhere we look. The prevailing theories hold that this cyclicity primarily represents the response of depositional processes to the rise and fall of sea level. In the rock record, geologists see times when sea level was astoundingly low alternating with times when sea level was much higher than today, and these anomalies often appear worldwide. For instance, during the depths of the last ice age 18,000 years ago when hundreds of thousands of cubic miles of ice were stacked up on the continents as glaciers, sea level was 120 m (390 ft) lower, locations that today support coral reefs were left high and dry, and coastlines were miles farther basinward from the present-day coastline. It was during this time of very low sea level that there was a dry land connection between Asia and Alaska over which humans are believed to have migrated to North America (see Bering Land Bridge).

However, for the past 6,000 years (a few centuries before the first known written records), the world's sea level has been gradually approaching the level we see today. During the previous interglacial about 120,000 years ago, sea level was for a short time about 6 m higher than today, as evidenced by wave-cut notches along cliffs in the Bahamas. There are also Pleistocene coral reefs left stranded about 3 metres above today's sea level along the southwestern coastline of West Caicos Island in the West Indies. These once-submerged reefs and nearby paleo-beach deposits are silent testimony that sea level spent enough time at that higher level to allow the reefs to grow (exactly where this extra sea water came from—Antarctica or Greenland—has not yet been determined). Similar evidence of geologically recent sea level positions is abundant around the world.

[edit] Estimates

See IPCC TAR, figure 11.4 for a graph of sea level changes over the past 140,000 years.^[18]

• The 2007 IPCC (Intergovernmental Panel on Climate Change) report suggested that sea levels would rise by between 19 cm (7.5 inches) and 59 cm by the end of this century.^[19]
• Sea-level rise estimates from satellite altimetry since 1992 (about 2.8 mm/yr) exceed those from tide gauges. It is unclear whether this represents an increase over the last decades, variability, or problems with satellite calibration.
• Church and White (2006) report an acceleration of SLR since 1870. ^[2] This is a revision since 2001, when the TAR stated that measurements have detected no significant acceleration in the recent rate of sea level rise.
• Based on tide gauge data, the rate of global average sea level rise during the 20th century lies in the range 0.8 to 3.3 mm/yr, with an average rate of 1.8 mm/yr.^[20]
• Recent studies of Roman wells in Caesarea and of Roman piscinae in Italy indicate that sea level stayed fairly constant from a few hundred years AD to a few hundred years ago.
• Based on geological data, global average sea level may have risen at an average rate of about 0.5 mm/yr over the last 6,000 years and at an average rate of 0.1 to 0.2 mm/yr over the last 3,000 years.
• Since the Last Glacial Maximum about 20,000 years ago, sea level has risen by over 120 m (averaging 6 mm/yr) as a result of melting of major ice sheets. A rapid rise took place between 15,000 and 6,000 years ago at an average rate of 10 mm/yr which accounted for 90 m of the rise; thus in the period since 20,000 years BP (excluding the rapid rise from 15-6 kyr BP) the average rate was 3 mm/yr.
• A significant event was Meltwater Pulse 1A (mwp-1A), when sea level rose approximately 20 m over a 500 year period about 14,200 years ago. This is a rate of about 40 mm/yr. Recent studies suggest the primary source was meltwater from the Antarctic, perhaps causing the south-to-north cold pulse marked by the Southern Hemisphere Huelmo/Mascardi Cold Reversal, which preceded the Northern Hemisphere Younger Dryas
• Relative sea level rise at specific locations is often 1-2 mm/yr greater or less than the global average. Along the US mid-Atlantic and Gulf Coasts, for example, sea level is rising approximately 3 mm/yr

[edit] U. S. Tide Gauge Measurements

U. S. Sea Level Trends 1900-2003

Tide gauges in the United States show considerable variation because some land areas are rising and some are sinking. For example, over the past 100 years, the rate of sea level rise varies from about an increase of 0.36 inches (9.1 mm) per year along the Louisiana Coast (due to land sinking), to a drop of a few inches per decade in parts of Alaska (due to post-glacial rebound). The rate of sea level rise increased during the 1993-2003 period compared with the longer-term average (1961-2003), although it is unclear whether the faster rate reflects a short-term variation or an increase in the long-term trend.^[21]

[edit] Amsterdam Sea Level Measurements

The longest running sea-level measurements are recorded at Amsterdam, in the Netherlands—most of which lies beneath sea level, hence the name. Records from 1700 onwards can be found at http://www.pol.ac.uk/psmsl/longrecords/longrecords.html. Since 1850, a rise of approx 1.5 mm/year is shown here.

[edit] Australian Sea Level Change

The London Royal Society calculates net sea level rise in Australia at 1 mm/yr^[22]—an important result for the Southern Hemisphere. The National Tidal Center also graphs 32 gauges, some since 1880, for the entire coastline^[23]

[edit] Future sea level rise

In 2007, the Intergovernmental Panel on Climate Change's Fourth Assessment Report predicted that by 2100, global warming will lead to a sea level rise of 19 to 58 cm^[24], depending on which of six possible world scenarios comes to pass.

These sea level rises could lead to difficulties for shore-based communities in the next centuries: for example, many major cities such as London and New Orleans already need storm-surge defenses, and would need more if sea level rose, though they also face issues such as sinking land.^[25] Sea level rise could also displace many shore-based populations: for example it is estimated that a sea level rise of just 20 cm could create 740,000 homeless people in Nigeria.^[26] Maldives, Tuvalu, and other low-lying countries are among the areas that are at the highest level of risk. The UN's environmental panel has warned that, at current rates, sea level would be high enough to make the Maldives uninhabitable by 2100.^{[27] [28]}

Future sea level rise, like the recent rise, is not expected to be globally uniform (details below). Some regions show a sea-level rise substantially more than the global average (in many cases of more than twice the average), and others a sea level fall.^[29] However, models disagree as to the likely pattern of sea level change.^[30]

[edit] Intergovernmental Panel on Climate Change results

The results from the IPCC Third Assessment Report (TAR) sea level chapter (convening authors John A. Church and Jonathan M. Gregory) are given below.

IPCC change factors 1990-2100	IS92a prediction	SRES prediction
Thermal expansion	110 to 430 mm
Glaciers	10 to 230 mm[31] (or 50 to 110 mm)[32]
Greenland ice	–20 to 90 mm
Antarctic ice	–170 to 20 mm
Terrestrial storage	–83 to 30 mm
Ongoing contributions from ice sheets in response to past climate change	0 to 55 mm
Thawing of permafrost	0 to 5 mm
Deposition of sediment	not specified
Total global-average sea level rise (IPCC result, not sum of above)[31]	110 to 770 mm	90 to 880 mm (central value of 480 mm)

The sum of these components indicates a rate of eustatic sea level rise (corresponding to a change in ocean volume) from 1910 to 1990 ranging from –0.8 to 2.2 mm/yr, with a central value of 0.7 mm/yr. The upper bound is close to the observational upper bound (2.0 mm/yr), but the central value is less than the observational lower bound (1.0 mm/yr), i.e., the sum of components is biased low compared to the observational estimates. The sum of components indicates an acceleration of only 0.2 (mm/yr)/century, with a range from –1.1 to +0.7 (mm/yr)/century, consistent with observational finding of no acceleration in sea level rise during the 20th century. The estimated rate of sea-level rise from anthropogenic climate change from 1910 to 1990 (from modeling studies of thermal expansion, glaciers and ice sheets) ranges from 0.3 to 0.8 mm/yr. It is very likely that 20th century warming has contributed significantly to the observed sea-level rise, through thermal expansion of sea water and widespread loss of land ice.^[31]

A common perception is that the rate of sea-level rise should have accelerated during the latter half of the 20th century, but tide gauge data for the 20th century show no significant acceleration. Estimates obtained are based on AOGCMs for the terms directly related to anthropogenic climate change in the 20th century, i.e., thermal expansion, ice sheets, glaciers and ice caps... The total computed rise indicates an acceleration of only 0.2 (mm/yr)/century, with a range from -1.1 to +0.7 (mm/yr)/century, consistent with observational finding of no acceleration in sea-level rise during the 20th century.^[33] The sum of terms not related to recent climate change is -1.1 to +0.9 mm/yr (i.e., excluding thermal expansion, glaciers and ice caps, and changes in the ice sheets due to 20th century climate change). This range is less than the observational lower bound of sea level rise. Hence it is very likely that these terms alone are an insufficient explanation, implying that 20th century climate change has made a contribution to 20th century sea level rise.^[15] Recent figures of human, terrestrial impoundment came too late for the 3rd Report, and would revise levels upward for much of the 20th century.

[edit] Uncertainties and criticisms regarding IPCC results

• Tide records with a rate of 180 mm/century going back to the 19th century show no measurable acceleration throughout the late 19th and first half of the 20th century. The IPCC attributes about 60 mm/century to melting and other eustatic processes, leaving a residual of 120 mm of 20th century rise to be accounted for. Global ocean temperatures by Levitus et al. are in accord with coupled ocean/atmosphere modelling of greenhouse warming, with heat-related change of 30 mm. Melting of polar ice sheets at the upper limit of the IPCC estimates could close the gap, but severe limits are imposed by the observed perturbations in Earth rotation. (Munk 2002)
• By the time of the IPCC TAR, attribution of sea-level changes had a large unexplained gap between direct and indirect estimates of global sea-level rise. Most direct estimates from tide gauges give 1.5–2.0 mm/yr, whereas indirect estimates based on the two processes responsible for global sea-level rise, namely mass and volume change, are significantly below this range. Estimates of the volume increase due to ocean warming give a rate of about 0.5 mm/yr and the rate due to mass increase, primarily from the melting of continental ice, is thought to be even smaller. One study confirmed tide gauge data is correct, and concluded there must be a continental source of 1.4 mm/yr of fresh water. (Miller 2004)
• From (Douglas 2002): "In the last dozen years, published values of 20th century GSL rise have ranged from 1.0 to 2.4 mm/yr. In its Third Assessment Report, the IPCC discusses this lack of consensus at length and is careful not to present a best estimate of 20th century GSL rise. By design, the panel presents a snapshot of published analysis over the previous decade or so and interprets the broad range of estimates as reflecting the uncertainty of our knowledge of GSL rise. We disagree with the IPCC interpretation. In our view, values much below 2 mm/yr are inconsistent with regional observations of sea-level rise and with the continuing physical response of Earth to the most recent episode of deglaciation."
• The strong 1997-1998 El Niño caused regional and global sea level variations, including a temporary global increase of perhaps 20 mm. The IPCC TAR's examination of satellite trends says the major 1997/98 El Niño-Southern Oscillation (ENSO) event could bias the above estimates of sea-level rise and also indicate the difficulty of separating long-term trends from climatic variability.^[33]

[edit] Glacier contribution

It is well known that glaciers are subject to surges in their rate of movement with consequent melting when they reach lower altitudes and/or the sea. The contributors to Annals of Glaciology [2], Volume 36 [3] (2003) discussed this phenomenon extensively and it appears that slow advance and rapid retreat have persisted throughout the mid to late Holocene in nearly all of Alaska's glaciers. Historical reports of surge occurrences in Iceland's glaciers go back several centuries. Thus rapid retreat can have several other causes than CO2 increase in the atmosphere.

The results from Dyurgerov show a sharp increase in the contribution of mountain and subpolar glaciers to sea level rise since 1996 (0.5 mm/yr) to 1998 (2 mm/yr) with an average of approx. 0.35 mm/yr since 1960.^[34]

Of interest also is Arendt et al.,^[35] who estimate the contribution of Alaskan glaciers of 0.14±0.04 mm/yr between the mid 1950s to the mid 1990s increasing to 0.27 mm/yr in the middle and late 1990s.

[edit] Greenland contribution

Krabill et al.^[36] estimate a net contribution from Greenland to be at least 0.13 mm/yr in the 1990s. Joughin et al.^[37] have measured a doubling of the speed of Jakobshavn Isbræ between 1997 and 2003. This is Greenland's largest-outlet glacier; it drains 6.5% of the ice sheet, and is thought to be responsible for increasing the rate of sea level rise by about 0.06 millimetres per year, or roughly 4% of the 20th century rate of sea level increase.^[38] In 2004, Rignot et al.^[39] estimated a contribution of 0.04±0.01 mm/yr to sea level rise from southeast Greenland.

Rignot and Kanagaratnam^[40] produced a comprehensive study and map of the outlet glaciers and basins of Greenland. They found widespread glacial acceleration below 66 N in 1996 which spread to 70 N by 2005; and that the ice sheet loss rate in that decade increased from 90 to 200 cubic km/yr; this corresponds to an extra 0.25 to 0.55 mm/yr of sea level rise.

In July 2005 it was reported^[41] that the Kangerdlugssuaq glacier, on Greenland's east coast, was moving towards the sea three times faster than a decade earlier. Kangerdlugssuaq is around 1,000 m thick, 7.2 km (4.5 miles) wide, and drains about 4% of the ice from the Greenland ice sheet. Measurements of Kangerdlugssuaq in 1988 and 1996 showed it moving at between 5 and 6 km/yr (3.1 to 3.7 miles/yr) (in 2005 it was moving at 14 km/yr [8.7 miles/yr]).

According to the 2004 Arctic Climate Impact Assessment, climate models project that local warming in Greenland will exceed 3° Celsius during this century. Also, ice sheet models project that such a warming would initiate the long-term melting of the ice sheet, leading to a complete melting of the Greenland ice sheet over several millennia, resulting in a global sea level rise of about seven metres.^[42]

[edit] Antarctic contribution

See also: Antarctica#Ice mass and global sea level

On the Antarctic continent itself, the large volume of ice present stores around 70 % of the world's fresh water.^[43] This ice sheet is constantly gaining ice from snowfall and losing ice through outflow to the sea. West Antarctica is currently experiencing a net outflow of glacial ice, which will increase global sea level over time. A review of the scientific studies looking at data from 1992 to 2006 suggested a net loss of around 50 Gigatonnes of ice per year was a reasonable estimate (around 0.14 mm of sea level rise).^[44] Although, significant acceleration of outflow glaciers in the Amundsen Sea Embayment could have more than doubled this figure for the year 2006.^[45]

East Antarctica is a cold region with a ground base above sea level and occupies most of the continent. This area is dominated by small accumulations of snowfall which becomes ice and thus eventually seaward glacial flows. The mass balance of the East Antarctic Ice Sheet as a whole is thought to be slightly positive (lowering sea level) or near to balance.^[44][45] However, increased ice outflow has been suggested in some regions.^[45][46]

[edit] Effects of snowline and permafrost

The snowline altitude is the altitude of the lowest elevation interval in which minimum annual snow cover exceeds 50%. This ranges from about 5,500 metres above sea-level at the equator down to sea-level at about 65° N&S latitude, depending on regional temperature amelioration effects. Permafrost then appears at sea-level and extends deeper below sea-level pole-wards. The depth of permafrost and the height of the ice-fields in both Greenland and Antarctica means that they are largely invulnerable to rapid melting. Greenland Summit is at 3,200 metres, where the average annual temperature is minus 32 °C. So even a projected 4 °C rise in temperature leaves it well below the melting point of ice. Frozen Ground 28, December 2004, has a very significant map of permafrost affected areas in the Arctic. The continuous permafrost zone includes all of Greenland, the North of Labrador, NW Territories, Alaska north of Fairbanks, and most of NE Siberia north of Mongolia and Kamchatka. Continental ice above permafrost is very unlikely to melt quickly. As most of the Greenland and Antarctic ice sheets lie above the snowline and/or base of the permafrost zone, they cannot melt in a timeframe much less than several millennia; therefore they are unlikely to contribute significantly to sea-level rise in the coming century.

[edit] Polar ice

The sea level will rise above its current level if more polar ice melts. However, compared to the heights of the ice ages, today there are very few continental ice sheets remaining to be melted. It is estimated that Antarctica, if fully melted, would contribute more than 60 metres of sea level rise, and Greenland would contribute more than 7 metres. Small glaciers and ice caps on the margins of Greenland and the Antarctic Peninsula might contribute about 0.5 metres. While the latter figure is much smaller than for Antarctica or Greenland it could occur relatively quickly (within the coming century) whereas melting of Greenland would be slow (perhaps 1,500 years to fully deglaciate at the fastest likely rate) and Antarctica even slower.^[13] However, this calculation does not account for the possibility that as meltwater flows under and lubricates the larger ice sheets, they could begin to move much more rapidly towards the sea.^[47][48]

In 2002, Rignot and Thomas^[49] found that the West Antarctic and Greenland ice sheets were losing mass, while the East Antarctic ice sheet was probably in balance (although they could not determine the sign of the mass balance for The East Antarctic ice sheet). Kwok and Comiso (J. Climate, v15, 487-501, 2002) also discovered that temperature and pressure anomalies around West Antarctica and on the other side of the Antarctic Peninsula correlate with recent Southern Oscillation events.

In 2004 Rignot et al.^[39] estimated a contribution of 0.04±0.01 mm/yr to sea level rise from South East Greenland. In the same year, Thomas et al.^[50] found evidence of an accelerated contribution to sea level rise from West Antarctica. The data showed that the Amundsen Sea sector of the West Antarctic Ice Sheet was discharging 250 cubic kilometres of ice every year, which was 60% more than precipitation accumulation in the catchment areas. This alone was sufficient to raise sea level at 0.24 mm/yr. Further, thinning rates for the glaciers studied in 2002-2003 had increased over the values measured in the early 1990s. The bedrock underlying the glaciers was found to be hundreds of metres deeper than previously known, indicating exit routes for ice from further inland in the Byrd Subpolar Basin. Thus the West Antarctic ice sheet may not be as stable as has been supposed.

In 2005 it was reported that during 1992-2003, East Antarctica thickened at an average rate of about 18 mm/yr while West Antarctica showed an overall thinning of 9 mm/yr. associated with increased precipitation. A gain of this magnitude is enough to slow sea-level rise by 0.12±0.02 mm/yr.^[51]

[edit] Effects of sea level rise

Based on the projected increases stated above, the IPCC TAR WG II report notes that current and future climate change would be expected to have a number of impacts, particularly on coastal systems.^[52] Such impacts may include increased coastal erosion, higher storm-surge flooding, inhibition of primary production processes, more extensive coastal inundation, changes in surface water quality and groundwater characteristics, increased loss of property and coastal habitats, increased flood risk and potential loss of life, loss of nonmonetary cultural resources and values, impacts on agriculture and aquaculture through decline in soil and water quality, and loss of tourism, recreation, and transportation functions.

There is an implication that many of these impacts will be detrimental—especially for the three-quarters of the world's poor who depend on agriculture systems. ^[53] The report does, however, note that owing to the great diversity of coastal environments; regional and local differences in projected relative sea level and climate changes; and differences in the resilience and adaptive capacity of ecosystems, sectors, and countries, the impacts will be highly variable in time and space.

Statistical data on the human impact of sea level rise is scarce. A study in the April, 2007 issue of Environment and Urbanization reports that 634 million people live in coastal areas within 30 feet (9.1 m) of sea level. The study also reported that about two thirds of the world's cities with over five million people are located in these low-lying coastal areas. The IPCC report of 2007 estimated that accelerated melting of the Himalayan ice caps and the resulting rise in sea levels would likely increase the severity of flooding in the short-term during the rainy season and greatly magnify the impact of tidal storm surges during the cyclone season. A sea-level rise of just 40 cm in the Bay of Bengal would put 11 percent of the Bangladesh's coastal land underwater, creating 7 to 10 million climate refugees.

[edit] Island nations

IPCC assessments suggest that deltas and small island states are particularly vulnerable to sea level rise caused by both thermal expansion and ocean volume. Relative sea level rise (mostly caused by subsidence) is currently causing substantial loss of lands in some deltas.^[54] Sea level changes have not yet been conclusively proven to have directly resulted in environmental, humanitarian, or economic losses to small island states, but the IPCC and other bodies have found this a serious risk scenario in coming decades.^[55]

Many media reports have focused the island nations of the Pacific, notably the Polynesian islands of Tuvalu, which based on more severe flooding events in recent years, was thought to be "sinking" due to sea level rise.^[56] A scientific review in 2000 reported that based on University of Hawaii gauge data, Tuvalu had experienced a negligible increase in sea-level of 0.07 mm a year over the past two decades, and that ENSO had been a larger factor in Tuvalu's higher tides in recent years.^[57] A subsequent study by John Hunter from the University of Tasmania, however, adjusted for ENSO effects and the movement of the gauge (which was thought to be sinking). Hunter concluded that Tuvalu had been experiencing sea-level rise of about 1.2 mm per year.^[57][58] The recent more frequent flooding in Tuvalu may also be due to an erosional loss of land during and following the actions of 1997 cyclones Gavin, Hina, and Keli.^[59]

Reuters has reported other Pacific islands are facing a severe risk including Tegua island in Vanuatu. Claims that Vanuatu data shows no net sea level rise, are not substantiated by tide gauge data. Vanuatu tide gauge data show a net rise of ~50 mm from 1994-2004. Linear regression of this short time series suggests a rate of rise of ~7 mm/y, though there is considerable variability and the exact threat to the islands is difficult to assess using such a short time series.

Numerous options have been proposed that would assist island nations to adapt to rising sea level.^[60]

[edit] Satellite sea level measurement

Satellite Measurement of Sea Level.

Red and white show where sea level has risen the most rapidly. Purple and blue where it has dropped.

Sea level rise estimates from satellite altimetry are 3.1 ± 0.4 mm/yr for 1993-2003 (Leuliette et al. (2004)). This exceeds those from tide gauges. It is unclear whether this represents an increase over the last decades; variability; true differences between satellites and tide gauges; or problems with satellite calibration.^[33] Knowing the current altitude of a satellite which can measure sea level to a precision of about 20 millimetres (e.g. the Topex/Poseidon system) is primarily complicated by orbital decay and the difference between the assumed orbit and the earth geoid ^[61]. This problem is partially corrected by regular re-calibration of satellite altimeters from land stations whose height from MSL is known by surveying. Over water, the height is calibrated from tide gauge data which is needed to correct for tides and atmospheric effects on sea level.