Hansen et al 2006 Global Temperature Changes

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Unformatted text preview: ysis of the University of East Anglia and the Hadley Centre (www.met-office.gov.uk r esearch h adleycentre obsdata globaltemperature.html) also yields high global temperature for 2005, but a few hundredths of a degree cooler than in 1998. Record, or near record, warmth in 2005 is notable, because global temperature did not receive a boost from an El Niño in 2005. The temperature in 1998, on the contrary, was lifted 0.2°C above the trend line by a ‘‘super El Niño’’ (see below), the strongest El Niño of the past century. Global warming is now 0.6°C in the past three decades and 0.8°C in the past century. It is no longer correct to say ‘‘most global warming occurred before 1940.’’ A better summary is: slow global warming, with large fluctuations, over the century up to 1975, followed by rapid warming at a rate 0.2°C per decade. Global warming was 0.7°C between the late 19th century (the earliest time at which global mean temperature can be accurately defined) and 2000, and continued warming in the first half decade of the 21st century is consistent with the recent rate of 0.2°C per decade. The conclusion that global warming is a real climate change, not an artifact due to measurements in urban areas, is confirmed by surface temperature change inferred from borehole temperature profiles at remote locations, the rate of retreat of alpine glaciers around the world, and progressively earlier breakup of ice on rivers and lakes (10). The geographical distribution of warming (Fig. 1B) provides further proof of real climate change. Largest warming is in remote regions including high latitudes. Warming occurs over ocean areas, far from direct human effects, with warming over ocean less than over land, an expected result for a forced climate change because of the ocean’s great thermal inertia. Early Climate Change Predictions. Manabe and Wetherald (11) made the first global climate model (GCM) calculations of warming due Author contributions: D.W.L. and M.M.-E. contributed data; J.H., M.S., R.R., K.L., D.W.L., and M.M.-E. analyzed data; and J.H. wrote the paper. The authors declare no conflict of interest. Freely available online through the PNAS open access option. Abbreviations: SST, sea surface temperature; GHG, greenhouse gas; EEP, Eastern Equatorial Pacific; WEP, Western Equatorial Pacific; DAI, dangerous antrhopogenic interference; BAU, business as usual; AS, alternative scenario; BC, black carbon. ‡To whom correspondence should be addressed: E-mail: jhansen@giss.nasa.gov. © 2006 by The National Academy of Sciences of the USA www.pnas.org cgi doi 10.1073 pnas.0606291103 A Global Land-Ocean Temperature Anomaly (°C) B 2001-2005 Mean Surface Temperature Anomaly (°C) to instant doubling of atmospheric CO2. The first GCM calculations with transient greenhouse gas (GHG) amounts, allowing comparison with observations, were those of Hansen et al. (12). It has been asserted that these calculations, presented in congressional testimony in 1988 (13), turned out to be ‘‘wrong by 300%’’ (14). That assertion, posited in a popular novel, warrants assessment because the author’s views on global warming have been welcomed in testimony to the United States Senate (15) and in a meeting with the Presi...
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This document was uploaded on 03/15/2014 for the course MEA 570 at N.C. State.

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