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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
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This document was uploaded on 03/15/2014 for the course MEA 570 at N.C. State.
- Spring '08