After a full week of presentations and discussions in Paris, the Intergovernmental Panel on Climate Change (IPCC) adopted the Summary for Policymakers of the first volume of “Climate Change 2007”, also known as the Fourth Assessment Report (AR4).
In stark terms it states: “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 levels.”
The report -“Climate Change 2007: The Physical Science Basis”-“assesses the current scientific knowledge of the natural and human drivers of climate change, observed changes in climate, the ability of science to attribute changes to different causes, and projections for future climate change,” said the organization’s press bulletin.
The report confirms, with a wealth of new data, that: 1) The temperature in the atmosphere and the oceans has grown warmer and can be expected to continue to do so. 2) The amount of greenhouse gasses, mainly CO2 and to some extent methane, have increased markedly since 1750. 3) These gasses are the most significant cause for the temperature increase. 4) Human activity is primarily responsible for their production.
The IPCC has in effect given the doubters on global warming hard evidence in the form of a causal chain of events, backed up by the most extensive studies yet done on all aspects of the world’s climate.
Specific portions of the IPCC’s 21-page summary of the report are as follows (some citations omitted):
“Changes in the atmospheric abundance of greenhouse gases and aerosols, in solar radiation and in land surface properties alter the energy balance of the climate system. These changes are expressed in terms of radiative forcing2, which is used to compare how a range of human and natural factors drive warming or cooling influences on global climate. Since the Third Assessment Report (TAR), new observations and related modeling of greenhouse gases, solar activity, land surface properties and some aspects of aerosols have led to improvements in the quantitative estimates of radiative forcing.”
“Carbon dioxide is the most important anthropogenic greenhouse gas. The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to 379 ppm3 in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The annual carbon dioxide concentration growth-rate was larger during the last 10 years (1995 – 2005 average: 1.9 ppm per year), than it has been since the beginning of continuous direct atmospheric measurements (1960-2005 average: 1.4 ppm per year) although there is year-to-year variability in growth rates.”
“The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land use change providing another significant but smaller contribution. Annual fossil carbon dioxide emissions4 increased from an average of 6.4 [6.0 to 6.8] GtC (23.5 [22.0 to 25.0] GtCO2) per year in the 1990s, to 7.2 [6.9 to 7.5] GtC (26.4 [25.3 to 27.5] GtCO2) per year in 2000-2005 (2004 and 2005 data are interim estimates).”
“The report,” said the IPCC bulletin, “was produced by some 600 authors from 40 countries. Over 620 expert reviewers and a large number of government reviewers also participated. Representatives from 113 governments reviewed and revised the Summary line-by-line during the course of this week before adopting it and accepting the underlying report.”
The Summary can be downloaded in English from www.ipcc.ch and http://ipcc-wg1.ucar.edu. A webcast of the final press conference has also been posted. The Summary will be available in Arabic, Chinese French, Russian and Spanish at a later date. Cambridge University Press will publish the full underlying report in English.
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