Feb, 2007

JTH 17-07-2001 3 COP6bis/SBSTA

Climate Change 2001: The Scientific BasisWGI contribution to IPCC Third Assessment Report

Summary for Policymakers (SPM)Drafted by a team of 59Approved ‘sentence by sentence’by WGI plenary (99 Governments and 45 scientists)

14 chapters881 pages120 Lead Authors515 Contributing Authors4621 References quoted

JTH 17-07-2001 4 COP6bis/SBSTA

SPM 3

2007

2001 (TAR)

• Anthropogenic contributions to aerosols (primarily sulphate,organic and black carbon, nitrate and dust)together produce a cooling effect, with a total direct radiative forcing of -0.5 [-0.9 to -0.1] W m -2 and an indirectcloud albedo forcing of -0.7 [-1.8 to -0.3] W m-2 . These forcings are now better understood than at the time ofthe TAR due to improved in situ, satellite and ground-based measurements and more comprehensive modeling,but remain the dominant uncertainty in radiative forcing. Aerosols also influence cloud lifetime and precipitation.

The understanding of anthropogenic warming and cooling influences on climate hasimproved since TAR, leading to very high confidence1 that the globally averaged neteffect of human activities since 1750 has been one of warming, with a radiative forcing of+ 1.6 [+0.6 to +2.4] W m-2

1 9 out of 10 chance of being correct

Soluble aerosoldeliquesce