Anthropogenic Anthropogenic Contributions to Future Sea Contributions to Future Sea

Level and TemperatureLevel and Temperature

Chase AsherChase Asher

Critical Literature ReviewCritical Literature Review

Geo 387H 12/7/06Geo 387H 12/7/06

OutlineOutline

IntroductionIntroduction

Sea Level ChangeSea Level Change Thermal ExpansionThermal Expansion Glacial MeltingGlacial Melting

Temperature ChangeTemperature Change Constant CompositionConstant Composition Constant EmissionConstant Emission

SummarySummary

SourcesSources

IntroductionIntroduction

Intergovernmental Panel on Climate Change Intergovernmental Panel on Climate Change released its Third Annual Report in 2001released 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 Helped to bring worldwide focus to the global warming

issue.issue.

Several people questioned the veracity of the Several people questioned the veracity of the claims of the TAR.claims of the TAR. Some claims of overestimation.Some claims of overestimation. Some models not applicable outside of a specific Some models not applicable outside of a specific

purpose (Melt model)purpose (Melt model)

Sea Level ChangeSea Level Change

Sea level change, even more than Sea level change, even more than temperature, affects people immediately.temperature, affects people immediately. Changing coastlinesChanging coastlines Changing fisheriesChanging fisheries

In the long term, sea level can also affect In the long term, sea level can also affect habitatshabitats Epipelagic zone would be altered, causing Epipelagic zone would be altered, causing

damage to existing coral reefs and other damage to existing coral reefs and other delicate ecosystems.delicate ecosystems.

Sea Level ChangeSea Level Change

Sea level rises through one of two Sea level rises through one of two methods:methods: Thermal expansion.Thermal expansion.

The physical result of heating the water. Like all The physical result of heating the water. Like all matter, it expands when heated.matter, it expands when heated.

Melting ice.Melting ice.Ice comes either from alpine glaciers, or ice sheets Ice comes either from alpine glaciers, or ice sheets such as those in Antarctica or Greenland.such as those in Antarctica or Greenland.

Thermal ExpansionThermal Expansion

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

Parallel Climate ModelParallel Climate Model

Older and more established of the two Older and more established of the two models.models.

Equilibrium climate sensitivity of 2.1˚ C Equilibrium climate sensitivity of 2.1˚ C

Transient Climate Response of 1.3˚ C Transient Climate Response of 1.3˚ C

Coarser resolution over land.Coarser resolution over land.

Worse parameterizations, but corresponds Worse parameterizations, but corresponds better with known data.better with known data.

Does not include meltwater.Does not include meltwater.

Community Climate System ModelCommunity Climate System Model

Newer modeling system.Newer modeling system.

Equilibrium climate sensitivity of 2.1˚ CEquilibrium climate sensitivity of 2.1˚ C

Transient climate response of 1.3˚ C Transient climate response of 1.3˚ C

Higher resolution.Higher resolution.

Better parameterization.Better parameterization.

Does not include meltwater.Does not include meltwater.

ComparisonComparison

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

ComparisonComparison

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

Glacial MeltingGlacial Melting

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

Glacial MeltingGlacial Melting

IPCC TAR used a melt model which is IPCC TAR used a melt model which is used in most studies with some used in most studies with some modifications.modifications.

Only takes into account glaciers and small Only takes into account glaciers and small ice caps (GSIC).ice caps (GSIC).

There is an empirical limitation which puts There is an empirical limitation which puts an artificial ceiling on melting after 2100.an artificial ceiling on melting after 2100.

Corrected TAR formulaCorrected TAR formula

The corrected TAR The corrected TAR formula created by formula created by Wigley and Raper solves Wigley and Raper solves this problem.this problem.Matches up well with Matches up well with original TAR formula original TAR formula before 2100.before 2100.Continues on realistically Continues on realistically afterwards, tending afterwards, tending asymptotically to the asymptotically to the initially available ice initially available ice volume.volume.

Results of New ModelResults of New Model

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

Glacier vs Ice Cap MeltingGlacier vs Ice Cap Melting

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

Temperature ChangeTemperature Change

Two Different ModelsTwo Different Models Constant CompositionConstant Composition

Assumes that no further green house gasses were Assumes that no further green house gasses were put into the atmosphere after 2000.put into the atmosphere after 2000.

An impossible model and extreme baseline An impossible model and extreme baseline prediction.prediction.

Constant EmissionConstant EmissionAssumes that emission rates for GHG’s remain Assumes that emission rates for GHG’s remain constant at 2000 levels.constant at 2000 levels.

A more realistic view of temperature change.A more realistic view of temperature change.

Constant CompositionConstant Composition

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

Constant EmissionConstant Emission

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

ConclusionsConclusions

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

Thank you!Thank you!

SourcesSourcesLiterature Sources:Literature Sources:1.1. Meehl , Gerald A et al. (2004)Meehl , Gerald A et al. (2004)How Much More Global Warming and Sea How Much More Global Warming and Sea Level Rise?Level Rise? Science, Vol 307, page 1769-1772. Science, Vol 307, page 1769-1772.2.2. Wigley, T.M.L.. (2004)Wigley, T.M.L.. (2004) The Climate Change Commitment The Climate Change Commitment. Science, Vol . Science, Vol 307, page 1766-1769.307, page 1766-1769.3.3. Kohfeld, Karen E. et al. (2004) Kohfeld, Karen E. et al. (2004) Role of Marine Biology in Glacial-Interglacial Role of Marine Biology in Glacial-Interglacial CO2 Cycles.CO2 Cycles. Science, Vol 308, page 74-78. Science, Vol 308, page 74-78.4.4. Wigley, T. M. L. and Raper, S. C. B. (2004) Wigley, T. M. L. and Raper, S. C. B. (2004) Extended scenarios for glacier Extended scenarios for glacier melt due to anthropogenic forcing. melt due to anthropogenic forcing. Geophysical Research Letters, Vol 32, L05704, Geophysical Research Letters, Vol 32, L05704, doi:10.1029/2004GL021238, 2005.doi:10.1029/2004GL021238, 2005.5.5. Hansen, James (2005) Hansen, James (2005) A slippery slope: How much global warming A slippery slope: How much global warming constitutes “Dangerous anthropogenic interference”?constitutes “Dangerous anthropogenic interference”? Climactic Change, Vol 68, 269- Climactic Change, Vol 68, 269-279.279.6.6. Koch, Dorothy and Hansen, James Koch, Dorothy and Hansen, James Distant origins of Arctic black carbon: A Distant origins of Arctic black carbon: A GoddardGoddardInstitute for Space Studies ModelE experiment. Institute for Space Studies ModelE experiment. JOURNAL OF GEOPHYSICAL JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D04204, doi:10.1029/2004JD005296, 2005RESEARCH, VOL. 110, D04204, doi:10.1029/2004JD005296, 20057. 7. Raper, S.C.B. and Braithwaite, Roger J. Raper, S.C.B. and Braithwaite, Roger J. Low sea level rise projections from Low sea level rise projections from mountainmountainglaciers and icecaps under global warming. glaciers and icecaps under global warming. Letters, Vol 439, 19 January 2006, Letters, Vol 439, 19 January 2006, doi:10.1038/nature04448doi:10.1038/nature04448