- There's a very high confidence (90%+ probability) that the net effect of human activities has been one of warming, with a net forcing effect of +1.6 W/m^2.
- The combined greenhouse gas effect is likely around +2.3 W/m^2 (with a 90% confidence interval of +2.07 to +2.53).
- Offsetting the warming is a global dimming effect due to aerosols and increased cloud cover of -1.2 W/m^2.
- The balance comes from other warming and cooling effects. The warming due to increased solar radiation is +0.12 W/m^2, about half the decrease of -0.2 W/m^2 due to changes in surface albedo (which I'm guessing means effects like desertification--don't know what happens to that number as ice melts.)
- Measurements show warming trends, increase in water vapor present in the atmosphere, and warming oceans (which have been absorbing 80% of the heat added to the system, causing the water to expand).
- Sea level rise from 1993-2003 is significantly higher than the rise from 1961-1993, driven mostly by thermal expansion and the Greenland and Antarctic ice sheets.
- Observed shifts in weather patterns are consistent with the temperature changes.
- From a paleoclimate point of view, "[t]he observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past fifty years can be explained without external forcing, and very likely that it is not due to natural forces alone." (emphasis omitted)
- Projected temperature increases for the period from 1990-2005 were between 0.15 and 0.3 deg. C per decade. The observed increase for that period has been 0.2 deg. C per decade, strengthening confidence in the projections.
- Warming tends to reduce the CO2 uptake by the land and oceans, leaving more CO2 in the atmosphere.
- Even at the current CO2 concentration, by the end of the century the best estimate of sea level rise is +0.3-0.9 meters. Other, greater CO2 scenarios show a rise of up to about 6 meters.
- Due to the time it takes natural processes to remove carbon from the atmosphere, both past and future carbon emissions will continue to contribute to warming for a millennium.
Friday, February 02, 2007
IPCC report on global warming
The Intergovernmental Panel on Climate Change has released a report on global warming. So far, I've been able to find only the Summary for Policymakers (pdf) available for download. Here are some things that jumped out at me during a quick read-through.