Global temperature change

Abstract

Global surface temperature has increased approximately 0.2 degrees C per decade in the past 30 years, similar to the warming rate predicted in the 1980s in initial global climate model simulations with transient greenhouse gas changes. Warming is larger in the Western Equatorial Pacific than in the Eastern Equatorial Pacific over the past century, and we suggest that the increased West-East temperature gradient may have increased the likelihood of strong El Niños, such as those of 1983 and 1998. Comparison of measured sea surface temperatures in the Western Pacific with paleoclimate data suggests that this critical ocean region, and probably the planet as a whole, is approximately as warm now as at the Holocene maximum and within approximately 1 degrees C of the maximum temperature of the past million years. We conclude that global warming of more than approximately 1 degrees C, relative to 2000, will constitute "dangerous" climate change as judged from likely effects on sea level and extermination of species.

Fig. 1.

Surface temperature anomalies relative to 1951–1980 from surface air measurements at meteorological stations and ship and satellite SST measurements. (A) Global annual mean anomalies. (B) Temperature anomaly for the first half decade of the 21st century.

Fig. 2.

Global surface temperature computed for scenarios A, B, and C (12), compared with two analyses of observational data. The 0.5°C and 1°C temperature levels, relative to 1951–1980, were estimated (12) to be maximum global temperatures in the Holocene and the prior interglacial period, respectively.

Fig. 3.

Comparison of SST in West and East Equatorial Pacific Ocean. (A) SST in 2001–2005 relative to 1870–1900, from concatenation of two data sets (5, 6), as described in the text. (B) SSTs (12-month running means) in WEP and EEP relative to 1870–1900 means.

Fig. 4.

Comparison of modern surface temperature measurements with paleoclimate proxy data in the WEP (28) (A), EEP (3, 30, 31) (B), Indian Ocean (40) (C), and Vostok Antarctica (41) (D).

Fig. 5.

Modern sea surface temperatures (5, 6) in the WEP compared with paleoclimate proxy data (28). Modern data are the 5-year running mean, while the paleoclimate data has a resolution of the order of 1,000 years.

Fig. 6.

Poleward migration rate of isotherms in surface observations (A and B) and in climate model simulations (17) for 2000–2100 for Intergovernmental Panel on Climate Change scenario A2 (10) and an alternative scenario of forcings that keeps global warming after 2000 less than 1°C (17) (C and D). Numbers in upper right are global means excluding the tropical band.