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GISS Surface Temperature Analysis

Global Temperature Trends: 2001 Summation

Figure 1

Figure 1: Global annual surface temperature relative to 1951-1980 mean based on surface air measurements at meteorological stations and satellite measurements of sea surface temperature.

Figure 2

Figure 2: Global map of temperature anomaly for 2001 meteorological year (Dec. 2000-Nov. 2001).

The 2001 meteorological year (December-November) had the second warmest global surface temperature (Fig. 1) in more than a century of instrumental data (see Hansen et al. 2001). Calendar year 2001 will also be the second warmest year on record, as the 11-month temperature anomaly exceeds that in the next warmest years (1990 and 1995) by almost 0.1°C. Our analysis uses recently documented procedures for data over land (Hansen et al. 2001) and for sea surface temperatures (Reynolds et al. 2002).

The global warmth in 2001 is particularly meaningful, because it occurs at a phase of the Southern Oscillation in which the tropical Pacific Ocean is cool (Fig. 2). The record warmth of 1998, in contrast, was bolstered by a strong El Niño that raised global temperature 0.2°C above the trend line (Fig. 1).

Global surface air warming in the past 25 years is now about 0.5°C, and in the past century it is about 0.75°C (Hansen et al. 2001). The recent surface warming contrasts with warming of only about 0.1°C in the troposphere over the past 22 years (Christy et al. 2000). However, surface and tropospheric warmings are similar over the past 50 years (NRC 2000).

The greatest warm anomalies in 2001 were in Alaska-Canada, in a band from North Africa to Central Asia, and the Antarctic peninsula (Palmer Land). The Indian and Western Pacific Oceans were unusually warm, continuing a trend of recent decades (Hansen et al. 2001).

The North Atlantic Ocean is notably warmer than the 1951-1980 climatology. Unusually cool conditions of recent decades, that had been centered in Baffin Bay and extended south and southeast of Greenland (Hansen et al. 2001), have given way to warm anomalies in the past five years.

Overall, the 2001 temperature extends the unusual global warming of recent decades. This warming is believed to be a consequence of anthropogenic greenhouse gases (IPCC 2001), and thus the high 2001 temperature can be expected to invigorate discussions about how to slow global warming.

This webpage was previously published as a letter to Science by Hansen et al. (2002).

Further Information

Related webpages on the GISS website include:


GISS scientists involved in this research were Drs. James E. Hansen Reto A. Ruedy and Makiko Sato.


Christy, J.R., R.W. Spencer, and W.D. Braswell 2000. J. Atmos. Oceanic Tech. 17, 1153.

Hansen, J., R. Ruedy, M. Sato, M. Imhoff, W. Lawrence, D. Easterling, T. Peterson, and T. Karl 2001. A closer look at United States and global surface temperature change. J. Geophys. Res. 106, 23947.

Hansen, J., R. Ruedy, Mki. Sato, and K. Lo 2002. Global warming continues. Science 295, 275.

Intergovernmental Panel on Climate Change 2001. Climate Change 2001 (J.T. Houghton et al., Eds.), Cambridge Univ. Press, New York.

National Research Council 2000. Reconciling Observations of Global Temperature Change. National Academy Press, Washington, DC, 85 pp.

Reynolds, R.W., N.A. Rayner, T.M. Smith, D.C. Stokes, and W. Wang 2002. An improved in situ and satellite SST analysis for climate. J. Climate 15, 1609-1625.