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Widening of the tropical belt in a changing climate


Some of the earliest unequivocal signs of climate change have been the warming of the air and ocean, thawing of land and melting of ice in the Arctic. But recent studies are showing that the tropics are also changing. Several lines of evidence show that over the past few decades the tropical belt has expanded. This expansion has potentially important implications for subtropical societies and may lead to profound changes in the global climate system. Most importantly, poleward movement of large-scale atmospheric circulation systems, such as jet streams and storm tracks, could result in shifts in precipitation patterns affecting natural ecosystems, agriculture, and water resources. The implications of the expansion for stratospheric circulation and the distribution of ozone in the atmosphere are as yet poorly understood. The observed recent rate of expansion is greater than climate model projections of expansion over the twenty-first century, which suggests that there is still much to be learned about this aspect of global climate change.

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Figure 1: What climatological features distinguish the tropics?
Figure 2: Changes in several estimates of the width of the tropical belt since 1979.


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We thank Celeste Johanson (University of Washington) for providing analysis of tropical widening trends in climate model simulations for the twenty-first century. The National Center for Atmospheric Research is sponsored by the US National Science Foundation. T.J.R. was supported by NSF grant ATM0532280 and by NOAA grant NA06OAR4310148. Q.F. is supported by NOAA Grant NA17RJ1232.

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Correspondence to Dian J. Seidel.

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Seidel, D., Fu, Q., Randel, W. et al. Widening of the tropical belt in a changing climate. Nature Geosci 1, 21–24 (2008).

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