SCIENTIFIC ASSESSMENTS AS INPUTS TO POLICY 1. Scientific Assessment of Ozone Depletion World Meteorological Organization (WMO) United Nations Environment Program (UNEP) Vienna Convention (1985) for Protection of the Ozone Layer 2. Intergovernmental Panel on Climate Change (WMO-UNEP) Framework Convention on Climate Change LEARNING FROM THE OZONE ASSESSMENT PROCESS Stratospheric Chemistry of Climatically Important Species O2 N2O CH4 CFCl3 CF2Cl2 H2O UV UV etc. O3 OH HO2 NO NO2 UV O2 O O2 HNO3 ClONO2 Cl ClO (ClO)2 HOCl N2O5 H2O2 HNO3 H2O HCl HCl O2 TROPOSPHERE Source/Greenhouse Gas Destructive Atom/Free Radical Benign Reservoir Gas Figure by MIT OCW, based on World Meteorological Organization: Global Ozone Research and Monitoring Project. CLIMATE CHANGE 2007: The Physical Science Basis Summary for Policymakers A. HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE ¾ Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture. ¾ The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect 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. B. OBSERVATIONS OF RECENT CLIMATE CHANGE ¾ Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level. ¾ At continental, regional, and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones. ¾ Some aspects of climate have not been observed to change: Diurnal temperature range, Antarctic sea ice extent, Antarctic atmospheric temperatures, meridional overturning circulation of the global ocean, tornadoes, hail, lightning and dust storms. ¾ Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 metres of sea level rise. C. UNDERSTANDING & ATTRIBUTING RECENT CLIMATE CHANGE ¾ Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns. ¾ Analysis of climate models together with constraints from observations enables an assessed likely range ( of 2 to 4.5oC ) to be given for climate sensitivity for the first time, and provides increased confidence in the understanding of the climate system response to radiative forcing. D. PROJECTIONS OF FUTURE CLIMATE CHANGE ¾ For the next two decades a warming of about 0.2oC per decade is projected for a range of SRES emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1o C per decade would be expected. ¾ Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century. ( Likely ranges are 2.4 to 6.4oC for a high emissions SRES scenario.) ¾ There is now higher confidence in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation, and some aspects of extremes and of ice. ¾ Anthropogenic warming and sea level rise would continue for centuries due to the timescales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.