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IPCC says climate change “unequivocal”

The Intergovernmental Panel on Climate Change (IPCC) has delivered its 2007 report. The Fourth Assessment Report concludes that the science and the conclusions are now more certain than in its last report and that global warming is now “unequivocal”.

David Miliband, Environment minister, said “It is another nail in the coffin of the climate change deniers and represents the most authoritative picture to date, showing that the debate over the science of climate change is well and truly over.”

Alan Thorpe, chief executive of the Natural Environment Research Council, said that “a handful of scientists, politicians and writers are still claiming humans are not responsible at all; we have got to kill off this notion so we can get on with the real work – protecting ourselves from future climate change”.

We reproduce here the highlighted parts of the summary report. For the full summary (22 pages) see the link at the end.

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.

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.

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.

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. This is an advance since the Third Assessment Report’s conclusion had been that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”.

Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.

Analysis of climate models together with constraints from observations enables an assessed likely range 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.

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.

For the next two decades a warming of about 0.2°C 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 0.1°C per decade would be expected.

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.

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.

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.

IPCC Summary Report

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