Hansen et al 2006 Global Temperature Changes

We first update our analysis of surface temperature

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Unformatted text preview: good indication of global temperature change. We first update our analysis of surface temperature change based on instrumental data and compare observed temperature change with predictions of global climate change made in the 1980s. We then examine current temperature anomalies in the tropical Pacific Ocean and discuss their possible significance. Finally, we compare paleoclimate and recent data, using the Earth’s history to estimate the magnitude of global warming that is likely to constitute dangerous human-made climate change. Modern Global Temperature Change Global surface temperature in more than a century of instrumental data is recorded in the Goddard Institute for Space Studies analysis for 2005. Our analysis, summarized in Fig. 1, uses documented procedures for data over land (4), satellite measurements of sea surface temperature (SST) since 1982 (5), and a ship-based analysis for earlier years (6). Estimated 2 error (95% confidence) in comparing nearby years of global temperature (Fig. 1 A), such as 1998 and 2005, decreases from 0.1°C at the beginning of the 20th century to 0.05°C in recent decades (4). Error sources include incomplete station coverage, quantified by sampling a modelgenerated data set with realistic variability at actual station locations (7), and partly subjective estimates of data quality problems (8). The estimated uncertainty of global mean temperature implies that we can only state that 2005 was probably the warmest year. The map of temperature anomalies for the first half-decade of the 21st century (Fig. 1B), relative to 1951–1980 climatology, shows that current warmth is nearly ubiquitous, generally larger over land than over ocean, and largest at high latitudes in the Northern Hemisphere. Our ranking of 2005 as the warmest year depends on the positive polar anomalies, especially the unusual Arctic warmth. In calculating the global mean, we give full weight to all regions based on area. Meteorological stations are sparse in the Arctic, but the estimated strong warm anomaly there in 2005 is consistent with 14288 –14293 PNAS September 26, 2006 vol. 103 no. 39 record low sea ice concentration and Arctic temperature anomalies inferred from infrared satellite data (9). Our analysis includes estimated temperature anomalies up to 1,200 km from the nearest measurement station (7). Resulting spatial extrapolations and interpolations of temperature anomalies usually are meaningful for seasonal and longer time scales at middle and high latitudes, where the spatial scale of anomalies is set by Rossby waves (7). Thus, we believe that the unusual Arctic warmth of 2005 is real. Other characteristics of our analysis method are summarized in Supporting Text, which is published as supporting information on the PNAS web site. Independent analysis by the National Climate Data Center (www.ncdc.noaa.gov oa climate research 2005 ann global. html), using a ‘‘teleconnection’’ approach to fill in data sparse regions, also finds 2005 to be the warmest year. The joint anal...
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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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