Anthropogenic Contributions to Future Sea Level and Temperature Chase Asher Critical Literature Review Geo 387H 12/7/06

Outline Introduction Sea Level Change Thermal Expansion Thermal Expansion Glacial Melting Glacial Melting Temperature Change Constant Composition Constant Composition Constant Emission Constant EmissionSummarySources

Introduction Intergovernmental Panel on Climate Change released its Third Annual Report in 2001 This featured the ‘hockey stick’ diagram. This featured the ‘hockey stick’ diagram. Helped to bring worldwide focus to the global warming issue. Helped to bring worldwide focus to the global warming issue. Several people questioned the veracity of the claims of the TAR. Some claims of overestimation. Some claims of overestimation. Some models not applicable outside of a specific purpose (Melt model) Some models not applicable outside of a specific purpose (Melt model)

Sea Level Change Sea level change, even more than temperature, affects people immediately. Changing coastlines Changing coastlines Changing fisheries Changing fisheries In the long term, sea level can also affect habitats Epipelagic zone would be altered, causing damage to existing coral reefs and other delicate ecosystems. Epipelagic zone would be altered, causing damage to existing coral reefs and other delicate ecosystems.

Sea Level Change Sea level rises through one of two methods: Thermal expansion. Thermal expansion. The physical result of heating the water. Like all matter, it expands when heated. Melting ice. Melting ice. Ice comes either from alpine glaciers, or ice sheets such as those in Antarctica or Greenland.

Thermal Expansion Small temperature changes (<1˚ C ) can equate to sea level changes measured in centimeters This increase in sea level is unavoidable, even if we were to stabilize atmospheric CO2. Two models discussed: Two models discussed: Parallel Climate Model Parallel Climate Model Community Climate System Model Community Climate System Model

Parallel Climate Model Older and more established of the two models. Equilibrium climate sensitivity of 2.1˚ C Transient Climate Response of 1.3˚ C Coarser resolution over land. Worse parameterizations, but corresponds better with known data. Does not include meltwater.

Community Climate System Model Newer modeling system. Equilibrium climate sensitivity of 2.1˚ C Transient climate response of 1.3˚ C Higher resolution. Better parameterization. Does not include meltwater.

Comparison B1, A1B, and A2 are differing levels of carbon dioxide. Even A1B would be a difficult target without reducing emissions to what they were before the nineties. Even for the case where CO2 stabilizes at 2000, the globe warms by.4C (PCM) or.6C (CCSM). CCSM’s higher sensitivity is clearly visible.

Comparison Global average temperature increases more in the CCSM model once again. Temperature increase in the North Atlantic especially is due to a decrease of meridional overturning, which causes a more defined thermocline and increased forcing.

Glacial Melting Glaciers melting are generally considered to be the source of most of the increase in sea level. Though one paper (Raper, 2006) disagrees and gives thermal expansion greater importance. In general, glacial surfaces melt much faster than ice sheets, due to an increased surface area to volume ratio.

Glacial Melting IPCC TAR used a melt model which is used in most studies with some modifications. Only takes into account glaciers and small ice caps (GSIC). There is an empirical limitation which puts an artificial ceiling on melting after 2100.

Corrected TAR formula The corrected TAR formula created by Wigley and Raper solves this problem. Matches up well with original TAR formula before Continues on realistically afterwards, tending asymptotically to the initially available ice volume.

Results of New Model Three different CO2 situations are shown in these graphs, as well as different mass balance sensitivities. Even after CO2 concentration stabilizes, radiative forcing continues to increase due to climate inertia.

Glacier vs Ice Cap Melting Raper claimed that it was not ice caps that were contributing to the rising sea level most, but glaciers. For three different initial volumes of glacial ice, glacial outpaced ice cap water for the next 600 years.

Temperature Change Two Different Models Constant Composition Constant Composition Assumes that no further green house gasses were put into the atmosphere after An impossible model and extreme baseline prediction. Constant Emission Constant Emission Assumes that emission rates for GHG’s remain constant at 2000 levels. A more realistic view of temperature change.

Constant Composition Even with constant composition, the climate is still catching up to its equilibrium warming commitment of.5 ˚ C. Following traditional physics it would never actually reach this equilibrium. Wigley creates a time dependent model, so the climate approaches it asymptotically. Climate sensitivity and aerosol forcing both affect the end result to an appreciable degree.

Constant Emission Increase in temperature is much more dramatic with increasing equilibrium temperature. Aerosol forcing is much weaker compared to climate sensitivity. Less asymptotic, more linear.

Conclusions Anthropogenic forcing is almost certainly altering the climate. The degree to which it is altering the climate is difficult to determine. Altering current emissions practices could have far reaching benefits, but fewer immediate ones. No one estimate for sea level rise or temperature is good on its own.

Thank you!

Sources Literature Sources: 1.Meehl, Gerald A et al. (2004)How Much More Global Warming and Sea Level Rise? Science, Vol 307, page Wigley, T.M.L.. (2004) The Climate Change Commitment. Science, Vol 307, page Kohfeld, Karen E. et al. (2004) Role of Marine Biology in Glacial-Interglacial CO2 Cycles. Science, Vol 308, page Wigley, T. M. L. and Raper, S. C. B. (2004) Extended scenarios for glacier melt due to anthropogenic forcing. Geophysical Research Letters, Vol 32, L05704, doi: /2004GL021238, Hansen, James (2005) A slippery slope: How much global warming constitutes “Dangerous anthropogenic interference”? Climactic Change, Vol 68, Koch, Dorothy and Hansen, James Distant origins of Arctic black carbon: A Goddard Institute for Space Studies ModelE experiment. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D04204, doi: /2004JD005296, Raper, S.C.B. and Braithwaite, Roger J. Low sea level rise projections from mountain glaciers and icecaps under global warming. Letters, Vol 439, 19 January 2006, doi: /nature04448