Inez Fung University of California, Berkeley April 2007 Global Warming Inez Fung University of California, Berkeley April 2007
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 29,000 time series from 75 studies, over 89% show changes consistent with the direction of change expected from warming
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
CO2 CH4 T Now 400,000 yr
At equilibrium: High CO2 --> warm; Low CO2 --> cold J. Hansen
The Last 500,000 years and the last 200 years J. Hansen
Global mean temperatures are rising faster with time Warmest 12 years: 1998,2005,2003,2002,2004,2006, 2001,1997,1995,1999,1990,2000 50 0.1280.026 100 0.0740.018 Period Rate Years /decade IPCC AR4
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
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
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
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
Projections of Climate Change 2020-2029 2090-2099 greatest over land & at most high N latitudes and least over the South. Ocean & parts of the N Atlantic Ocean IPCC AR4
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
Stern Review 2006
2000 2020 Stern Review 2006
Strong action is needed urgently Stern Review 2006 Strong action is needed urgently