Climate change and trace gases

[Simon]

Trace atmospheric gases have played a leading role in climate change throughout Earth's history. Thus, empirical data on trace gas histories and climate change provide invaluable information on climate sensitivity. The Earth's climate history also provides our best indication of the level of global warming that would constitute 'dangerous interference' with climate. The empirical data, abetted by appropriate calculations, imply that control of trace gases must play a critical role in preserving a planet resembling the one on which civilization developed.

Warning: This is a scientific article (Philosophical Transactions of The Royal Society, Volume 365, Number 1856 / 15 July 2007), not journalism. The full article is also available in PDF[/url:56870]. Here's the Abstract for you, with my emphasized parts:

Palaeoclimate data show that the Earth's climate is remarkably sensitive to global forcings. Positive feedbacks predominate. This allows the entire planet to be whipsawed between climate states. One feedback, the 'albedo flip' property of ice/water, provides a powerful trigger mechanism. A climate forcing that 'flips' the albedo of a sufficient portion of an ice sheet can spark a cataclysm. Inertia of ice sheet and ocean provides only moderate delay to ice sheet disintegration and a burst of added global warming. Recent greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures. Carbon dioxide (CO2) is the largest human-made climate forcing, but other trace constituents are also important. Only intense simultaneous efforts to slow CO2 emissions and reduce non-CO2 forcings can keep climate within or near the range of the past million years. The most important of the non-CO2 forcings is methane (CH4), as it causes the second largest human-made GHG climate forcing and is the principal cause of increased tropospheric ozone (O3), which is the third largest GHG forcing. Nitrous oxide (N2O) should also be a focus of climate mitigation efforts. Black carbon ('black soot') has a high global warming potential (approx. 2000, 500 and 200 for 20, 100 and 500 years, respectively) and deserves greater attention. Some forcings are especially effective at high latitudes, so concerted efforts to reduce their emissions could preserve Arctic ice, while also having major benefits for human health, agricultural productivity and the global environment.

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