Climate Change: Recent News
• Feb 7 2007: United Nations Env Programme - Intergovt Panel on Climate Change - observed warming since the 20thC is very likely due to anthropogenic greenhouse gases
• April 2 2007: US Supreme Court: anthropogenic CO2 is a pollutant
• April 7 2007: UNEP IPCC WG 2 - warming has had discernible influence on physical and biological systems
Changing Composition of the Atmosphere
Analysis of ancient air bubbles trapped in ice
Direct measurements of atm composition in the past centuries
Increases since 1800 due to human activities
Global mean temperatures are rising faster with time
100 0.0740.018
50 0.1280.026
Warmest 12 years:1998,2005,2003,2002,2004,200
6, 2001,1997,1995,1999,1990,200
0
Period Rate
Years /decade
IPCC AR4
The most important spatial pattern (top) of the monthly Palmer Drought Severity Index (PDSI) for 1900 to 2002.
The time series (below) accounts for most of the trend in PDSI.
Drought is increasing most places
Mainly decrease in rain over land in tropics and
subtropics, but enhanced by increased atmospheric demand
with warming
IPCC AR4
Climate Feedbacks
Warming
Evaporation from ocean,Increase water vapor in atmEnhance greenhouse effect
Decrease snow cover;Decrease reflectivity of surfaceIncrease absorption of solar energy
Increase cloud cover;Decrease absorption of solar energy
AttributionAttribution
• are observed changes consistent with
expected responses to forcings
inconsistent with alternative explanations
Observations
Climate model: All forcing
Climate model: Solar+volcanic only
IPCC AR4
greatest over land & at most high N latitudes
and least over the South. Ocean & parts of the N Atlantic Ocean
Projections of Climate Change
IPCC AR4
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