1. Inez Fung University of California, Berkeley April 2007
Global Warming
Inez Fung
University of California, Berkeley
April 2007

2. Climate Change: Recent News
Feb : United Nations Env Programme - Intergovt Panel on Climate Change - observed warming since the 20thC is very likely due to anthropogenic greenhouse gases
April : US Supreme Court: anthropogenic CO2 is a pollutant
April : UNEP IPCC WG 2 - warming has had discernible influence on physical and biological systems
29,000 time series from 75 studies, over 89% show changes consistent with the direction of change expected from warming

3. 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

4. CO2
CH4 T
Now
400,000 yr

5. At equilibrium: High CO2 --> warm; Low CO2 --> cold
J. Hansen

6. The Last 500,000 years and the last 200 years
J. Hansen

7. Global mean temperatures are rising faster with time
Warmest 12 years:
1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000
0.026
0.018
Period Rate
Years /decade
IPCC AR4

8. Drought is increasing most places
Mainly decrease in rain over land in tropics and subtropics, but enhanced by increased atmospheric demand with warming
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.
IPCC AR4

9. Climate Feedbacks Evaporation from ocean, Increase water vapor in atm
Increase cloud cover;
Decrease absorption of solar energy
Evaporation from ocean,
Increase water vapor in atm
Enhance greenhouse effect
Warming
Decrease snow cover;
Decrease reflectivity of surface
Increase absorption of solar energy

10. Attribution are observed changes consistent with
Observations
are observed changes consistent with
expected responses to forcings
inconsistent with alternative explanations
Climate model: All forcing
Climate model: Solar+volcanic only
Attribution of climate change to causes involves READ
Climate models are important tools for attributing and understanding climate change. Understanding observed changes is based on our best understanding of climate physics, as contained in simple to complex climate models. For the 4rth assessment report, we had a new and very comprehensive archive of 20th century simulations available. This has greatly helped.
This figure gives an example.
You see observed global and annual mean temperature in black over the 20th century compared to that simulated by a wide range of these models. On the top, in red, are individual model simulations and their overall mean shown fat, that are driven by external influences including increases in greenhouse gases, in aerosols, in changes in solar radiation and by volcanic eruptions. The observations rarely leave the range of model simulations. The trends and individual events like cooling in response to volcanic eruptions (POINT) are well reproduced. The fuzzy range gives an idea of uncertainty with variability in the climate system.
IPCC AR4

11. Projections of Climate Change
Best estimate for low scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C).
IPCC AR4

12. Projections of Climate Change
greatest over land & at most high N latitudes
and least over the
South. Ocean
& parts of the
N Atlantic
Ocean
IPCC AR4

13. Warming is faster than model projections: Recent rapid melting glaciers on Greenland
Not included in IPCC model because this observation was made after the IPCC models have completed their model development phase and have started the lengthy integrations. Other processes not included, such as reduced capacities of land and ocean to store carbon, all contribute to accelerating global warming.
i.e. global warming projections in IPCC AR4 are slower than what we might expect now.
Jay Zwally

14. Stern Review 2006

15. 2000
2020
Stern Review 2006

16. Strong action is needed urgently
Stern Review 2006
Strong action is needed urgently