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An Inconvenient Truth An Inconvenient Truth DiscussionDiscussion

Lis Cohen Lis Cohen Department of MeteorologyDepartment of Meteorology

University of UtahUniversity of [email protected]@utah.edu

mailto:[email protected]


Summary and Summary and CommentsComments


Overall ImpressionOverall Impression

• Very Very well doneVery Very well done– Climate change is a complicated topicClimate change is a complicated topic– The science is often hard to explainThe science is often hard to explain

• Gore did a very good job explaining the fundamentals of Gore did a very good job explaining the fundamentals of the sciencethe science

• Gore did a very good job explaining the urgency of the Gore did a very good job explaining the urgency of the situationsituation

• Most of my criticisms are very nitpickyMost of my criticisms are very nitpicky– These critiques should not substantially weaken the These critiques should not substantially weaken the

credibility of this movie.credibility of this movie.– The science and importance of global warming is well The science and importance of global warming is well

portrayed.portrayed.– RealClimate.org (complete discussion)RealClimate.org (complete discussion)


Global Climate ChangeGlobal Climate Change

• There is no longer any There is no longer any scientific doubt that the scientific doubt that the Earth’s average surface Earth’s average surface temperature is increasingtemperature is increasing

– 1.31.3°°F in last centuryF in last century

– Recent decades warmer than Recent decades warmer than any comparable period in last any comparable period in last 400 years (possibly much longer) 400 years (possibly much longer)

• Ocean temperature, ice and snow cover, and sea Ocean temperature, ice and snow cover, and sea level changes consistent with this global warminglevel changes consistent with this global warming– Sea level up 7 inches in 20Sea level up 7 inches in 20thth century century


Causes of Recent Climate Causes of Recent Climate ChangeChange• There is There is very high confidencevery high confidence that that

human-generated increases in human-generated increases in greenhouse gas concentrations are greenhouse gas concentrations are responsible for responsible for mostmost of the global of the global warming observed during the past 50 warming observed during the past 50 yearsyears

• It is It is very unlikelyvery unlikely that natural climate that natural climate variations alone, such as changes in the variations alone, such as changes in the brightness of the sun, have produced brightness of the sun, have produced this recent warmingthis recent warming


Invasive species, disease and Invasive species, disease and global warmingglobal warming

• Invasive species due to Invasive species due to land use change and land use change and importationimportation

• Not sure how invasive Not sure how invasive plants and insects will plants and insects will respondrespond


Lack of cloud modeling Lack of cloud modeling uncertainties in the movieuncertainties in the movie


Ice Core and COIce Core and CO22

• Long ice core records of COLong ice core records of CO22 and temperature in Antarctic and temperature in Antarctic ice coresice cores

• View 1: other climate forcings View 1: other climate forcings besides CObesides CO22 contribute to the contribute to the change in Antarctic change in Antarctic temperature between glacial temperature between glacial and interglacial climate. and interglacial climate.

• View 2: Gore is careful not to View 2: Gore is careful not to state what the state what the temperature/COtemperature/CO22 scaling is. scaling is.


Aerosol Concentrations in ice Aerosol Concentrations in ice corescores

• Gore claims that you can Gore claims that you can see the aerosol see the aerosol concentrations in Antarctic concentrations in Antarctic ice cores change "in just ice cores change "in just two years", due to the U.S. two years", due to the U.S. Clean Air Act. Clean Air Act.

• You can't see dust and You can't see dust and aerosols at all in Antarctic aerosols at all in Antarctic cores — not with the naked cores — not with the naked eyeeye


COCO22 and Temperature and Temperature connections in the ice core connections in the ice core

recordrecord• Observed long-term relationship Observed long-term relationship

between CObetween CO22 and temperature in and temperature in Antarctica supports our Antarctica supports our understanding of the warming understanding of the warming impact of increased COimpact of increased CO22 concentrations concentrations

• Moreover, our knowledge of why Moreover, our knowledge of why COCO22 is changing now (fossil fuel is changing now (fossil fuel burning) is solid. burning) is solid.

• Carbon cycle Carbon cycle – COCO22 is a greenhouse gas is a greenhouse gas– Carbon cycle feedback is positive Carbon cycle feedback is positive

(increasing temps lead to increasing (increasing temps lead to increasing COCO22 and CH and CH44))

– Future changes in COFuture changes in CO22 will be larger will be larger than we might anticipate.than we might anticipate.


Climate impacts on the Climate impacts on the ocean conveyorocean conveyor

• Timing is uncertain. Timing is uncertain. • Younger Dryas 11,000 y.a.Younger Dryas 11,000 y.a.

– A large discharge of fresh water A large discharge of fresh water into the North Atlantic disrupted into the North Atlantic disrupted currents, causing significant currents, causing significant regional cooling. regional cooling.

• IPCC predicts a slowdown in IPCC predicts a slowdown in the circulation ~ 30% by 2100the circulation ~ 30% by 2100– Circulation modeling and future Circulation modeling and future

inputs of melted ice -not well inputs of melted ice -not well understood. understood.

– Few scientists are willing to Few scientists are willing to completely rule out the completely rule out the possibility of a more substantial possibility of a more substantial change in the future.change in the future.


Ice-sheet driven sea level Ice-sheet driven sea level riserise

• Gore correctly asserted that melting of Gore correctly asserted that melting of Greenland or the West Antarctic ice Greenland or the West Antarctic ice sheet would raise sea levels 20ft (6 sheet would raise sea levels 20ft (6 meters). meters). – No time frame, very uncertainNo time frame, very uncertain– 20 ft 20 ft

•about how much higher sea level was around about how much higher sea level was around 125,000 years ago during the last inter-glacial 125,000 years ago during the last inter-glacial period. period.

– Then, global temperatures were only a degree or two Then, global temperatures were only a degree or two warmer than todaywarmer than today


Impact of sea ice retreat on Impact of sea ice retreat on Polar bearsPolar bears

• Summer Arctic sea ice Summer Arctic sea ice shattered all records this year shattered all records this year for the minimum extent. for the minimum extent.

• Polar bears Polar bears – depend on the sea ice depend on the sea ice

• hunt for seals in the spring and hunt for seals in the spring and summersummer

– disappearance ice disappearance ice • likely to impact them severelylikely to impact them severely

– Studying the regional populations Studying the regional populations of polar bears is not easy and of polar bears is not easy and assessing their prospects is tough. assessing their prospects is tough.

• Arctic ecosystemsArctic ecosystems are are changingchanging on many different levels. on many different levels. – It may be the smaller and less It may be the smaller and less

photogenic elements that have the photogenic elements that have the biggest impact. –RealClimate.orgbiggest impact. –RealClimate.org


Pacific island nations Pacific island nations needing to evacuateneeding to evacuate

• Much of Tuvalu Much of Tuvalu – is only a few feet above sea levelis only a few feet above sea level– With more sea level riseWith more sea level rise

• increasing brine in groundwaterincreasing brine in groundwater• increasing damage and coastal increasing damage and coastal

erosion from tides and storm surgeserosion from tides and storm surges

• Government of Tuvalu asked Government of Tuvalu asked New Zealand to be ready to New Zealand to be ready to evacuate islandersevacuate islanders

• In the movie: "That's why the In the movie: "That's why the citizens of these pacific citizens of these pacific nations have all had to nations have all had to evacuate to New Zealand“.evacuate to New Zealand“.


KilimanjaroKilimanjaro• Ongoing discussion in the

literature:– Is retreat of ice on Kilimanjaro

related to the direct effects of climate change? • warming atmospheric temperatures

– Or indirect effects of climate change• altered patterns of humidity, cloud

cover, and precipitation influencing Kilimanjaro's ice mass

• Take home message– (a) ice field that we know has

existed for at least the past 12,000 years is shrinking

– (b) most of the other glaciers are disappearing as well.

Feb 1993

Feb 2000

http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/kilimanjaro_etm_93_00.jpg


Drying up of Lake ChadDrying up of Lake Chad

• ExtremesExtremes– DroughtsDroughts– FloodingFlooding

• Lake Chad Change Lake Chad Change – reduction of rainfall across entire Sahel from reduction of rainfall across entire Sahel from

1950s to 1980s1950s to 1980s– rainfall today still substantially below high point 50 rainfall today still substantially below high point 50

years agoyears ago– Other factorsOther factors

• Irrigation and upstream water use. Irrigation and upstream water use. • Substantial evidence that at least a portion of this drying Substantial evidence that at least a portion of this drying

out is human-caused. out is human-caused. • Indian Ocean changes in sea surface temperatureIndian Ocean changes in sea surface temperature• Increase in atmospheric aerosols in the Northern Increase in atmospheric aerosols in the Northern

hemisphere.hemisphere.

http://www.dailymail.co.uk/pages/live/articles/news/worldnews.html?in_article_id=479576&in_page_id=1811


Hurricane Katrina and Hurricane Katrina and global warmingglobal warming

• Katrina is usedKatrina is used– Destructive power of hurricanesDestructive power of hurricanes– Cope with natural disasterCope with natural disaster– Ex. of what could get worse in a Ex. of what could get worse in a

warmer world. warmer world.

• Nowhere does Gore state that Nowhere does Gore state that Katrina was caused by global Katrina was caused by global warming. warming. – Individual hurricanes cannot be Individual hurricanes cannot be

attributed to global warming, but the attributed to global warming, but the statistics of hurricanes, in particular statistics of hurricanes, in particular the maximum intensities attained by the maximum intensities attained by storms, may be. storms, may be.

http://geology.com/news/images/hurricane-katrina-satellite-image.jpg


Impact of ocean warming Impact of ocean warming on coral reefson coral reefs

• Stress FactorsStress Factors– OverfishingOverfishing– deliberate destructiondeliberate destruction– water pollutionwater pollution– sea level risesea level rise– ocean acidification ocean acidification – warming oceans. warming oceans. – That rising temperatures and other factors cause coral That rising temperatures and other factors cause coral

bleaching is true. bleaching is true.

• Bleaching episodes happen when the coral is Bleaching episodes happen when the coral is under stress, and many examples have been under stress, and many examples have been linked to anomalously warm ocean temperatureslinked to anomalously warm ocean temperatures

http://web.syr.edu/~tjconena/coral_reefs.htm


Priority Actions for American Priority Actions for American ConsumersConsumers• Vote!Vote!

• TransportationTransportation– Choose a place to live that reduces the Choose a place to live that reduces the

need to drive.need to drive.– Think twice before purchasing another Think twice before purchasing another

car. car. – Choose a fuel efficient, low polluting car. Choose a fuel efficient, low polluting car. – Set concrete goals for reducing your Set concrete goals for reducing your

travel. travel. – Whenever practical walk, bicycle or take Whenever practical walk, bicycle or take

public transportation public transportation – Brower, 1999Brower, 1999


Priority Actions for American Priority Actions for American ConsumersConsumers

• FoodFood– Eat less meat.Eat less meat.– Buy certified organic produce.Buy certified organic produce.

• Household OperationsHousehold Operations– Choose your home carefully.Choose your home carefully.– Reduce the environmental costs of Reduce the environmental costs of heating and hot water. heating and hot water. – Install efficient lighting and appliancesInstall efficient lighting and appliances– Choose an electricity supplier offering renewable energy.Choose an electricity supplier offering renewable energy.

• PolicyPolicy– Vote, write letters, attend rallies, call your representatives Vote, write letters, attend rallies, call your representatives

and express your views. and express your views. – Brower, 1999Brower, 1999


SummarySummary

• Climate Change will Climate Change will impact Utah in a impact Utah in a variety of ways.variety of ways.

• An Inconvenient Truth An Inconvenient Truth did a great job did a great job explaining climate explaining climate change. change.

• Most of my comments Most of my comments are very nitpickyare very nitpicky

• You can help slow You can help slow down climate change! down climate change!

• Take Action Today!Take Action Today!


Thank you!Thank you!

[email protected]@utah.edu


mailto:[email protected]

http://www.weatheroutreach.org/


Background SlidesBackground Slides


Old ideas about cooling Old ideas about cooling earthearth• The reason scientists thought the earth was The reason scientists thought the earth was

cooling was because they had just discovered the cooling was because they had just discovered the milankovic cycles and saw sea core bed data that milankovic cycles and saw sea core bed data that indicated we might be due for another ice age. indicated we might be due for another ice age. The didn't know about the fact that many of the The didn't know about the fact that many of the components of the milancovic cycle all needed to components of the milancovic cycle all needed to fall in phase for the ice age to begin. fall in phase for the ice age to begin.

• Temps decreased for about 30 years and Temps decreased for about 30 years and scientists were just starting to look at climate scientists were just starting to look at climate data. data.

• Few scientists thought this was happening with a Few scientists thought this was happening with a lot of press. lot of press.


Reference: CO2 changes Reference: CO2 changes during the ice agesduring the ice ages

• A A fullfull understanding of why CO2 changes understanding of why CO2 changes in precisely the pattern that it does during in precisely the pattern that it does during ice ages is elusive, but among the most ice ages is elusive, but among the most plausible explanations is that increased plausible explanations is that increased received solar radiation in the southern received solar radiation in the southern hemisphere due to changes in Earth's hemisphere due to changes in Earth's orbital geometry warms the southern orbital geometry warms the southern ocean, releasing CO2 into the atmosphere, ocean, releasing CO2 into the atmosphere, which then leads to further warming which then leads to further warming through an enhanced greenhouse effect. through an enhanced greenhouse effect.


British JudgeBritish Judge

• The judge appears to have put words in The judge appears to have put words in Gore's mouth that would indeed have Gore's mouth that would indeed have been wrong been wrong had they been saidhad they been said (but they (but they weren't). weren't).

• The judge was really ruling on how The judge was really ruling on how "Guidance Notes" for teachers should be "Guidance Notes" for teachers should be provided to allow for more in depth provided to allow for more in depth discussion of these points in the discussion of these points in the classroom. classroom.



• Gore uses this example to illustrate that there are Gore uses this example to illustrate that there are droughts in some regions even while other areas are droughts in some regions even while other areas are flooding. flooding.

• Unfortunately this is what models suggest.Unfortunately this is what models suggest.

• The dominant causeThe dominant cause– reduction of rainfall across entire Sahel from 1950s to 1980sreduction of rainfall across entire Sahel from 1950s to 1980s– rainfall today still substantially below high point 50 years agorainfall today still substantially below high point 50 years ago– Other factorsOther factors

• Irrigation and upstream water use. Irrigation and upstream water use. • Substantial evidence that at least a portion of this drying out is Substantial evidence that at least a portion of this drying out is

human-caused. human-caused. – Recent papers (Recent papers (Held et al, PNASHeld et al, PNAS; ; Chung and RamanathanChung and Ramanathan and and

BiasuttiBiasutti and and GianniniGiannini) have addressed causes ranging) have addressed causes ranging• Indian Ocean changes in sea surface temperatureIndian Ocean changes in sea surface temperature• Increase in atmospheric aerosols in the Northern hemisphere.Increase in atmospheric aerosols in the Northern hemisphere.

http://www.gfdl.noaa.gov/%7Eih/papers/sahel_pnas_pub.pdf

http://eddycom.ucsd.edu/publication/2007GL030491.pdf

http://iri.columbia.edu/%7Ealesall/pubslist/biagia_grl2006.pdf




Impact of sea ice retreat on Impact of sea ice retreat on Polar bearsPolar bears

• Summer Arctic sea ice Summer Arctic sea ice shatteredshattered all records this year for the minimum extent. all records this year for the minimum extent. – This was partially related to wind patterns favorable to ice export in the spring, but This was partially related to wind patterns favorable to ice export in the spring, but

the long term trends are almost certainly related to the ongoing and dramatic the long term trends are almost certainly related to the ongoing and dramatic warming in the Arctic. warming in the Arctic.

• Polar bears do indeed depend on the sea ice to hunt for seals in the spring and Polar bears do indeed depend on the sea ice to hunt for seals in the spring and summer, and so a disappearance of this ice is likely to impact them severely. summer, and so a disappearance of this ice is likely to impact them severely.

• The specific anecdote referred to in the movie came from The specific anecdote referred to in the movie came from observationsobservations of of anomalous drownings of bears in 2004 and so was accurate. anomalous drownings of bears in 2004 and so was accurate.

• However, studying the regional populations of polar bears is not easy and However, studying the regional populations of polar bears is not easy and assessing their prospects is tough. assessing their prospects is tough. – In the best observed populations such as in western Hudson Bay (In the best observed populations such as in western Hudson Bay (StirlingStirling

and Parkinson, 2006 and Parkinson, 2006), female polar bear weight is going down as the sea ice ), female polar bear weight is going down as the sea ice retreats over the last 25 years, and the FWS is retreats over the last 25 years, and the FWS is consideringconsidering an endangered species an endangered species listing. listing.

– However, it should be stated that in most of the discussions about polar bears, they However, it should be stated that in most of the discussions about polar bears, they are used as a representative species. are used as a representative species.

• Take home message: Arctic ecosystems are changing on Take home message: Arctic ecosystems are changing on many different levels. In the end, it may be the smaller many different levels. In the end, it may be the smaller and less photogenic elements that have the biggest and less photogenic elements that have the biggest impact. impact.

http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html

http://www.springerlink.com/content/p235r60mu4878820/

http://neptune.gsfc.nasa.gov/publications/pdf/pubs2006/Stirling%20-%20Possible%20Effects%20of%20Climate%20Warming.pdf

http://neptune.gsfc.nasa.gov/publications/pdf/pubs2006/Stirling%20-%20Possible%20Effects%20of%20Climate%20Warming.pdf

http://www.biologicaldiversity.org/swcbd/species/polarbear/Proposed-Rule.pdf



• Gore uses this example to illustrate that there are Gore uses this example to illustrate that there are droughts in some regions even while other areas droughts in some regions even while other areas are flooding. are flooding.

• Unfortunately this is what models suggest.Unfortunately this is what models suggest.

• The dominant causeThe dominant cause– reduction of rainfall across entire Sahel from 1950s to reduction of rainfall across entire Sahel from 1950s to

1980s1980s– rainfall today still substantially below high point 50 rainfall today still substantially below high point 50

years agoyears ago– Other factorsOther factors

• Irrigation and upstream water use. Irrigation and upstream water use. • Substantial evidence that at least a portion of this drying out is Substantial evidence that at least a portion of this drying out is

human-caused. human-caused. • Indian Ocean changes in sea surface temperatureIndian Ocean changes in sea surface temperature• Increase in atmospheric aerosols in the Northern hemisphere.Increase in atmospheric aerosols in the Northern hemisphere.


Impact of ocean warming Impact of ocean warming on coral reefson coral reefs

• Stress FactorsStress Factors– OverfishingOverfishing– deliberate destructiondeliberate destruction– water pollutionwater pollution– sea level risesea level rise– ocean acidification ocean acidification – warming oceans. warming oceans. – That rising temperatures and other factors cause coral That rising temperatures and other factors cause coral

bleaching is true. bleaching is true. – Bleaching episodes happen when the coral is under stress, and Bleaching episodes happen when the coral is under stress, and

many examples have been linked to anomalously warm ocean many examples have been linked to anomalously warm ocean temperatures (Australia in 1998 and 2002, all over the Indian temperatures (Australia in 1998 and 2002, all over the Indian Ocean in recent years). Corals are a sobering example of how Ocean in recent years). Corals are a sobering example of how climate change exacerbates existing vulnerabilities in eco-climate change exacerbates existing vulnerabilities in eco-systems, potentially playing the role of the straw that breaks systems, potentially playing the role of the straw that breaks the camel's back in many instances. the camel's back in many instances.


Figure 1. Model Simulation of Trend in Hurricanes (from Knutson et al, 2004)

http://www.gfdl.noaa.gov/reference/bibliography/2004/tk0401.pdf

www.WeatherOutreach.orgwww.WeatherOutreach.orgFigure 2. Measure of total power dissipated annually by tropical cyclones in the North Atlantic (the power dissipation index "PDI") compared to September tropical North Atlantic SST (from Emanuel, 2005)


Can giant hurricanes exist all around Can giant hurricanes exist all around the world like in the Day After the world like in the Day After Tomorrow?Tomorrow?

• Clusters of thunderstorms cannot Clusters of thunderstorms cannot merge together to form a continent-merge together to form a continent-scale blizzard with a calm eye over scale blizzard with a calm eye over land.land.

• Huge storms with calm eyes happen Huge storms with calm eyes happen over the oceans not over land. over the oceans not over land. – Hurricanes or Tropical StormsHurricanes or Tropical Storms

•Require that the core of the storm be over Require that the core of the storm be over warm ocean waterwarm ocean water

Photo: earthobservatory.nasa.gov/NaturalHazards/Arch...


What process could most likely change the What process could most likely change the climate?climate?

Warmer climate More evaporation at the equator

More moisture in the air

More moisture can be held in the air

More rain at higher latitudesMore freshwater

in the ocean

Ocean is not as salty and dense

Water does not sink in the northern latitudes

Circulation slows down

and changes

Melting Glaciers


Three Glaciers RetreatingThree Glaciers Retreating

• Source: C.L. Andrews. 1912, 1938. Denver Glacier: Source: C.L. Andrews. 1912, 1938. Denver Glacier: From the From the Glacier Photograph CollectionGlacier Photograph Collection . Boulder, . Boulder, CO: National Snow and Ice Data Center. Digital CO: National Snow and Ice Data Center. Digital Media; Marion T. Millett. 1958. Denver Glacier: From Media; Marion T. Millett. 1958. Denver Glacier: From the the Glacier Photograph CollectionGlacier Photograph Collection . Boulder, CO: . Boulder, CO: National Snow and Ice Data Center. Digital Media. National Snow and Ice Data Center. Digital Media.

Denver Glacier in Recession, Denver Glacier in Recession, Alaska, British ColumbiaAlaska, British Columbia

1912 1912

19381938

http://nsidc.org/data/g00472.html

http://nsidc.org/data/g00472.html


Temperature and Ice Temperature and Ice Accumulation vs. TimeAccumulation vs. Time


Data SourcesData Sources

• The 2007 IPCC (Intergovernmental Panel on The 2007 IPCC (Intergovernmental Panel on Climate Change) report Climate Change) report – IncludesIncludes

• 2,500 + scientific expert reviewers2,500 + scientific expert reviewers• 800+ contributing authors800+ contributing authors• 450+ lead authors from 450+ lead authors from • 130+ different countries130+ different countries• 6 years of work 6 years of work • 4 volumes 4 volumes • 1 report1 report

• Scientific LiteratureScientific Literature• Presentations from experts at the University of Presentations from experts at the University of

Utah – Dr. Dave Chapman, Dr. Tim Garrett, Dr. Utah – Dr. Dave Chapman, Dr. Tim Garrett, Dr. Gerald Mace, Dr. Thomas ReichlerGerald Mace, Dr. Thomas Reichler


Temperature AnalysisTemperature Analysis

• ““Warming of the climate system Warming of the climate system is unequivocal, as is now evident is unequivocal, as is now evident from observations of increases in from observations of increases in global average air and ocean global average air and ocean temperatures, widespread temperatures, widespread melting of snow and ice, and melting of snow and ice, and rising global average sea level” rising global average sea level” (IPCC report 2007). (IPCC report 2007).


Contributions to Sea Level Contributions to Sea Level RiseRise


Long-term Changes in Long-term Changes in ClimateClimate• Long-term changes are observed at: Long-term changes are observed at:

– Continental ScalesContinental Scales– Regional ScalesRegional Scales– Ocean basin ScalesOcean basin Scales

• These changes include:These changes include:– Changes in Arctic temperatures and iceChanges in Arctic temperatures and ice– Widespread changes in precipitation amountsWidespread changes in precipitation amounts– Ocean salinityOcean salinity– Wind patterns Wind patterns – Aspects of extreme weatherAspects of extreme weather

• DroughtsDroughts• Heavy precipitationHeavy precipitation• Heat wavesHeat waves• Intensity of tropical cyclonesIntensity of tropical cyclones

- 2007 IPCC report- 2007 IPCC report


What can change our What can change our climate?climate?• Changes in these factors alter the Changes in these factors alter the

energy balance of the climate system:energy balance of the climate system:– Solar radiationSolar radiation– Land surface propertiesLand surface properties– The atmospheric abundance of The atmospheric abundance of

greenhouse gases and aerosolsgreenhouse gases and aerosols

-2007 IPCC Report-2007 IPCC Report


The Greenhouse EffectThe Greenhouse Effect


How are greenhouse gas How are greenhouse gas impacts measured?impacts measured?

• These impacts are expressed in These impacts are expressed in terms of radiative forcing, which is terms of radiative forcing, which is used to compare how a range of used to compare how a range of human and natural factors drive human and natural factors drive warming or cooling influences on warming or cooling influences on global climate.global climate.


LOSU = level of understandingRF = Radiative Forcing

Error bars

Additional forcing factors not included here are considered to have a very low level of scientific understand.


How is the sun affecting How is the sun affecting climate change?climate change?

The effect of the sun’s variations accounts for +.12 W/m2.

There is very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W/m2.

Natural Climate Variability because of the sun has been not very significant.


How do we know that this How do we know that this is not a normal cycle?is not a normal cycle?

We use past climate data and We use past climate data and compare influencing factors.compare influencing factors.


How do we know about past How do we know about past climates?climates?

• Tree Rings – Growth is controlled by temperature, Tree Rings – Growth is controlled by temperature, precipitation and sunlightprecipitation and sunlight

• Pollens – give a good indication of what was living at Pollens – give a good indication of what was living at the time indicating a temperature rangethe time indicating a temperature range

• Ice and sea bed cores – Gasses in bubbles, dust, Ice and sea bed cores – Gasses in bubbles, dust, isotopes, accumulation rateisotopes, accumulation rate

• The fossil record The fossil record • Coral bedsCoral beds

Note: Uncertainties generally increase with time into Note: Uncertainties generally increase with time into the past due to increasingly limited spatial coverage. the past due to increasingly limited spatial coverage.


Paleoclimate InformationPaleoclimate Information

““Paleoclimate information supports the Paleoclimate information supports the interpretation that the warmth of the interpretation that the warmth of the last half century is unusual in at least last half century is unusual in at least the previous 1300 years.” the previous 1300 years.”

““The last time the polar regions were The last time the polar regions were significantly warmer than present for an significantly warmer than present for an extended period (about 125,000 years ago), extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 reductions in polar ice volume led to 4 to 6 meters (13-20 feet) of sea level rise.” meters (13-20 feet) of sea level rise.”

-2007 IPCC Report -2007 IPCC Report


What has Changed and What has Changed and what has Not Changed?what has Not Changed?


Aspects of climate that have NOT Aspects of climate that have NOT changedchanged

• Day night temperature differences have remained Day night temperature differences have remained constant. Both the maximum and minimum constant. Both the maximum and minimum temperatures have increased at the same rate. The temperatures have increased at the same rate. The trends are highly variable from one region to trends are highly variable from one region to another. another.

• Antarctic sea ice extent continues to show inter-Antarctic sea ice extent continues to show inter-annual variability and localized changes but no annual variability and localized changes but no statistically significant average trends, consistent statistically significant average trends, consistent with the lack of warming reflected in atmospheric with the lack of warming reflected in atmospheric temperatures averaged across the region.temperatures averaged across the region.

• There is insufficient evidence to determine whether There is insufficient evidence to determine whether trends exist intrends exist in– Meridional overturning circulation of the global oceanMeridional overturning circulation of the global ocean– Small scale phenomena Small scale phenomena

• TornadoesTornadoes• HailHail• Lightning Lightning • Dust-stormsDust-storms


Ward Hunt Ice Shelf, 2002

Consequences of Climate Change


Muir Inlet, AlaskaMuir Inlet, Alaska

National Snow and Ice data centerhttp://nsidc.org/cgi-bin/gpd_run_pairs.pl

20042004

19411941

Glacier Bay National Park and Preserve

Larsen B ice shelf, AntarcticaLarsen B ice shelf, Antarcticaca. 100 x 80 milesca. 100 x 80 miles

Mar. 5, 2002Mar. 5, 2002Feb. 17, 2002Feb. 17, 2002

Larsen B ice shelf,Larsen B ice shelf,AntarcticaAntarctica


Arctic Polar Ice CapArctic Polar Ice Cap

• Since 1979, the size of the summer polar ice cap has shrunk Since 1979, the size of the summer polar ice cap has shrunk more than 20 percent. more than 20 percent.

• On Sept. 21, 2005, sea ice extent dropped to 2.05 million sq. On Sept. 21, 2005, sea ice extent dropped to 2.05 million sq. miles, the lowest extent yet recorded in the satellite record.miles, the lowest extent yet recorded in the satellite record.

• ThisThis loss is twice the size of Texas. loss is twice the size of Texas.

1979

http://www.nasa.gov/centers/goddard/news/topstory/2003/1023esuice.html

2003


NAS

A


ReferencesReferences

• Climate Change 2007: The Physical Climate Change 2007: The Physical Science Basis. Intergovernmental Panel Science Basis. Intergovernmental Panel on Climate Change.on Climate Change.

• Garrett, T. “Rapid Arctic Climate ChangeGarrett, T. “Rapid Arctic Climate ChangeForcing the Feedbacks.” 2007. Forcing the Feedbacks.” 2007.

• Chapman, D. “Global Warming – Just Hot Chapman, D. “Global Warming – Just Hot Air?” 2006.Air?” 2006.

•


Thank you!Thank you!

Questions?Questions?Presentation can be found at: Presentation can be found at:

www.WeatherOutreach.org/2.htmlwww.WeatherOutreach.org/2.htmlLis Cohen: [email protected] Cohen: [email protected]


Alaska Tundra Travel Days

Decreased by Half

Since 1970


Changes in Greenhouse Gases Changes in Greenhouse Gases from Ice-Core and Modern Datafrom Ice-Core and Modern Data

The global The global increases in carbon increases in carbon dioxide dioxide concentration are concentration are due primarily to due primarily to fossil fuel use and fossil fuel use and land-use change.land-use change.


Changes in Greenhouse GasesChanges in Greenhouse Gases

The increases of methane and nitrous oxide are primarily due to agriculture.

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