IPCC Intergovernmental Panel on Climate Change

•Established by UN Environmental Program and the World Meteorlogical Society in 1988•Consists of 2000 experts in appropriate fields•3 working groups: I assess the scientific issues II evaluate impact on global climate change III risk management and mitigation•Third Assessment: January 2001•Fourth Assessment Feb 2007 was the point at which conclusive evidence convinced most that the climate is changing due to anthropogenic causes (debate ended overall besides in the political and economic arenas and a minority of skeptic scientists)

Atmospheric Structure

IPCC Assessments

• Third Assessment 2001: Human activities are influencing global climate change

• Fourth Assessment 2007: – global climate change is now occurring– caused by rising levels of anthropogenic

greenhouse gases– global impacts will be unprecedented and

severe

Impacts of Global Warming

• Melting of polar ice caps

• Flooding of coastal areas

• Massive migrations of people inland

• Alteration of rainfall patterns

• Deserts becoming farmland and farmland becoming deserts

• Significant losses in crop yields

The Earth as a Greenhouse

Greenhouse Gases and Sources ranked by highest radiative

forcing to lowest• Water vapor• CO2• Methane• Nitrous oxide*• CFCs and other

halocarbons*

• Hydrological cycle• fossil fuel, respiration• Animal husbandry• Chemical fertilizers*• Refrigerants*

* = contribute to ozone depletion in stratosphere as well

Radiative Forcing (Watts/m2)positive forcing leads to warmingnegative forcing leads to cooling

Radiative forces relates energy into vs. energy leaving tropospherepositive forcing leads to warmingnegative forcing leads to cooling

Sulfate aerosols result from chemical reactions in the atmosphere of SO2 from fossil fuel burning and have a short life in the air (so only localized cooling effects)

Current CO2 levels are 387 ppm (or 387,000 ppb)

35% higher than before industrial revolution and higher than any time in the last 400,000 years (see next slide)

Thus our insulating blanket is thicker and it is reasonable to expect higher temperatures to follow

Methane CH4 level have more than doubled since before the industrial revolution and likely more than in last 400,000 yrs also

Global Carbon CycleData is given in GtC (billion metric tons of carbon).

Carbon pools are in the boxes, and fluxes are indicated by the arrows.

Evidences of Climatic Change• 17 of the hottest years on record have occurred since

1980 (Fig. 20-5)• Since mid 1970s, average global temp has risen 0.6oC

(1.1oF) and 0.8oC (1.4oF) over last century (remember 5oC swings between ice ages and warm periods)

• Wide-scale recession of glaciers• Dramatic temp. increases in northern latitudes and

melting of permafrost• Sea level rising• Increased severity of extreme weather? (hurricanes,

monsoons, flooding, droughts, etc)

IPCC Predicted mean global temperature changeby 2100 is between 1.5 and 4.5 Co

Fourth Assessment CO2 Concentrations from Mona Loa Observatory

Why seasonal variation (the wiggle in the graph)? …with CO2 rising in fall and winter and CO2 decreasing in spring and summer.

Comparison between actual temperature data (thick black line) and the runs of 13 models shown in color

The “hockey stick” curve of temp over last 1000 years

IPCC Report: Model Projections of global mean warming with various scenarios from “commitment” where GHG’

Climates in the Past

Key Findings of the Fourth Assessment

• Increased warming – climate change• Differing regional impacts• Heat waves more frequent and last longer• Vulnerable ecosystems - arctic• Widespread water concerns – increase in extremes (+

and -) of daily precipitation• Agriculture largely unaffected• Thermohaline conveyor system expected to slow down• Rising sea levels• Storm intensities expected to increase

Arctic Climate Impact Assessment in 2004

• Arctic climate is now warming rapidly (twice as fast as global mean and 4-7oC in next 100 yrs)

• Arctic warming and its consequences will have worldwide implications

• Arctic vegetation zones will shift, and animal ranges and distribution will change (aquatic and terrestrial)

• Reduced sea ice and earlier seasonal melting likely to increase marine transport and access to resources

• Thawing ice & permafrost will disrupt transportation, buildings, and other infrastructure

Decline of Arctic Sea Ice

Tracking sea ice at the end of northern summer by satellite images….decline of more than 8% per decade

Arctic Albedo Feedback loop positive radiative forcing

What About the Antarctic?

• Holds most of the world’s ice– Could be a huge factor in future sea level rise– Although unlikely to fully melt, Greenland and

Antarctic ice sheets hold enough water to raise sea level by 230 feet…for perspective

• Losing as much as 36 cubic miles of ice/year – enough to raise sea level by 0.4mm/year

Response I to Climate: Mitigation

• Framework Convention on Climate Change• Kyoto Protocol & Copenhagen Climate Conf• U.N. Climate Control Conference• U.S. Policy

– Global Climate Change Initiative– Climate Change Science Program– National Climate Change Technology Initiative

Response 2: Adaptation

• Reduced crop yields

• Water scarcity

• Increased heat and moisture infectious diseases and lethal heat waves

• Increased intensity and severity of storm events

• Impoverished nations will be most affected – adaptation not an option