Global Warming Cause for Concern Cause for Concern

Global Warming Cause for Concern

Cause for Concern? What is the effect of increased levels of carbon dioxide in the Earth’s atmosphere? Nobody knows for sure

Cause for Concern? Scientists are concerned for three reasons: 1. Climate models predict climate change 2. There are observed changes in climate 3. Pre-historic studies show a correlation between atmospheric CO 2 levels and global climate What is Climate?

3. Cause for Concern? Climate models

Climate Models What is a computer model of the climate? © Australian Bureau of Meteorology

Climate Models Reflected by clouds, atmosphere (~23%) Emitted IR radiation Natural greenhouse heating Greenhouse gases (2. 5 Wm-2) Input solar radiation (100 %) Absorbed by atmosphere (20%) ~60 Wm-2 Measured absorption (25%) ~80 Wm-2 ? ? Reflected from surface (~8%) Absorbed by ground (~49%)

Climate Models What is the output of a climate model?

Cause for Concern? Observed Changes in Climate

Observed Changes Average surface temperature is difficult to measure

Observed changes It is difficult to detect small changes in a long series of data?

Observed changes Best estimates

Other observations UEA December Press Release 2005 The global combined sea surface temperature (SST) and land surface air temperature anomaly for 2005, with respect to the 1961 -1990 average, to the end of November has been +0. 48°C. 2005 is currently the second warmest year on record and 2005 is likely to be among the warmest 4 years in the official temperature record since 1861, but final figures will not be released until February. The last 10 years (19962005), with the exception of 1996, are the warmest years on record. The anomaly so far for the Northern Hemisphere is 0. 65°C and for the Southern Hemisphere 0. 32°C. The current 2005 values for the Northern Hemisphere make it the warmest on record and the current value for the Southern Hemisphere make it the fourth warmest. Table 1. a shows the 10 warmest years using our official figures, for each region. Table 1. b shows the 11 warmest years using simple area averaged data, including the value for January to November 2005, for each region. Out of the past ten years, only 1996 does not fall in the ten warmest – its place is taken by 1995.

Other observations UEA December Press Release 2005 The global combined sea surface temperature (SST) and land surface air temperature anomaly for 2005, with respect to the 1961 -1990 average, to the end of November has been +0. 48°C. 2005 is currently the second warmest year on record and 2005 is likely to be among the warmest 4 years in the official temperature record since 1861, but final figures will not be released until February. The last 10 years (1996 -2005), with the exception of 1996, are the warmest years on record. The anomaly so far for the Northern Hemisphere is 0. 65°C and for the Southern Hemisphere 0. 32°C. The current 2005 values for the Northern Hemisphere make it the warmest on record and the current value for the Southern Hemisphere make it the fourth warmest. Table 1. a shows the 10 warmest years using our official figures, for each region. Table 1. b shows the 11 warmest years using simple area averaged data, including the value for January to November 2005, for each region. Out of the past ten years, only 1996 does not fall in the ten warmest – its place is taken by 1995.

Other observations UEA December Press Release 2005

Other observations • Germany

Other observations • Argentina

Cause for Concern? Prehistoric Studies

Pre-Historic studies Bubbles in Artic Ice Maximum Value 300 ppm Minimum Value 180 ppm Ice Ages

Atmospheric CO 2 Concentration versus year Current value 370 ppm variation in the last 400, 000 years

Causes for concern • • • Climate models Observed changes Pre-historic climate studies

Carbon dioxide Can we be completely sure that the climate changes we observe are caused by anthropogenic emissions of carbon dioxide? Not completely sure But it is likely:

Climate Models Predictions What do climate models lead us to expect?

Climate Models What is the current effect of CO 2 • A net extra ‘forcing’ of around 2 watts per square metre… Average 240 W/m 2 150 W/m 2 + 2 W/m 2 On Average 390 W/m 2

An additional 2 watts per square metre of ‘radiative forcing’ • Scientific American March 2004

Contributions to Climate Forcing (W/m 2) -1 0 +1 Carbon Dioxide Greenhouse gases Methane Chlorofluorocarbons Nitrous Oxide Ozone Black Carbon Aerosols Reflective aerosols Cloud droplet changes Land cover changes Sun

Feedback Increased Climate Forcing Increased Water Vapour Positive Climate Forcing Global Temperature Negative Decreased Climate Forcing Increased Cloud Cover More Evaporation

The Future… CO 2 levels will rise • Very roughly, – If we make a 50% cut in GLOBAL emissions – CO 2 will stabilise at twice historical levels • Probably the best we can hope for in the next century.

IPCC Predictions…