Here is the final 2007 IPCC report:
ipcc.ch
Opening:
Summary for Policymakers of the Synthesis Report of the IPCC Fourth Assessment Report
DRAFT COPY 16 NOVEMBER 2007 23:04 – Subject to final copyedit
Introduction
This Synthesis Report is based on the assessment carried out by the three Working Groups of the IPCC. It provides
an integrated view of climate change as the final part of the IPCC?s Fourth Assessment Report.
A complete elaboration of the topics covered in this summary can be found in this Synthesis Report and in the
underlying reports of the three Working Groups.
1. Observed changes in climate and their effects
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 average sea level
(Figure SPM.1). {1.1}
Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of
global surface temperature (since 1850). The 100-year linear trend (1906-2005) of 0.74 [0.56 to 0.92]°C 1 is larger
than the corresponding trend of 0.6 [0.4 to 0.8]?C (1901-2000) given in the Third Assessment Report (TAR)
(Figure SPM.1). The temperature increase is widespread over the globe, and is greater at higher northern latitudes.
Land regions have warmed faster than the oceans (Figures SPM.2, SPM.4). {1.1, 1.2}
Rising sea level is consistent with warming (Figure SPM.1). Global average sea level has risen since 1961 at an
average rate of 1.8 [1.3 to 2.3]mm/yr and since 1993 at 3.1 [2.4 to 3.8]mm/yr, with contributions from thermal
expansion, melting glaciers and ice caps, and the polar ice sheets. Whether the faster rate for 1993 to 2003 reflects
decadal variation or an increase in the longer-term trend is unclear. {1.1}
Observed decreases in snow and ice extent are also consistent with warming (Figure SPM.1). Satellite data since
1978 show that annual average Arctic sea ice extent has shrunk by 2.7 [2.1 to 3.3]% per decade, with larger
decreases in summer of 7.4 [5.0 to 9.8]% per decade. Mountain glaciers and snow cover on average have declined
in both hemispheres. {1.1}
From 1900 to 2005, precipitation increased significantly in eastern parts of North and South America, northern
Europe and northern and central Asia but declined in the Sahel, the Mediterranean, southern Africa and parts of
southern Asia. Globally, the area affected by drought has likely2 increased since the 1970s. {1.1}
It is very likely that over the past 50 years: cold days, cold nights and frosts have become less frequent over most
land areas, and hot days and hot nights have become more frequent. It is likely that: heat waves have become more
frequent over most land areas, the frequency of heavy precipitation events has increased over most areas, and since
1975 the incidence of extreme high sea level3 has increased worldwide. {1.1}
There is observational evidence of an increase in intense tropical cyclone activity in the North Atlantic since about
1970, with limited evidence of increases elsewhere. There is no clear trend in the annual numbers of tropical
cyclones. It is difficult to ascertain longer term trends in cyclone activity, particularly prior to 1970.
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23 pages long.... |
