Regional Rainfall in a Warming World

Slowly but surely, a picture of climate change at the regional scale -- where it really matters -- is beginning to take shape.

Apart from the obvious warming at the high polar latitudes, which already is affecting Arctic sea ice, the rate of Greenland ice cap melting, and Antarctic ice shelves, new details are beginning to emerge about the impact of global warming in the Tropics -- the boiler-room of Earth's climate and weather.

This is the home of El Niño, and the generator of Asian monsoons, the towering cumulonimbus storms that deliver water vapor to the atmosphere and drive patterns of rainfall over much of the world.

In the March issue of the Journal of Climate, a team of University of Hawaii researchers led by meteorologist Shang-Ping Xie offers a preliminary look at what a relatively uniform warming does to a climate system that is chock o'block with regional patches of hot and cold and wet and dry.

From a series of simulations of computer models of different design, here is a robust pattern of enhanced rainfall across the equatorial Pacific during the first half of the 21st Century under a "business and usual" scenario of carbon dioxide emissions. (Click on it for a more detailed look at the patchwork the rainfall pattern and the contours of warmer and cooler temperatures.)

The basin-wide bands of heightened rainfall and warm temperatures looks somewhat like El Nino, although the timing and scale and potential impacts could be different. In an email, Xie draws the analogy, but makes a distinction:

Tropical anomalies during El Niño have strong impacts on US climate, inducing dry conditions in the Pacific Northwest and floods in California, among other things. Exact effects of SST warming patterns on US rainfall are under investigation.

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