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A 10-year timeout for global warming, study says

The German research effort is one of the first to attempt 10-year climate forecasts.

By Peter N. SpottsStaff writer of The Christian Science Monitor / May 1, 2008

Not warm yet: These sunbathers along Germany's Baltic Coast may have at least a decade of stable temperatures before the climate begins to warm, according to a new study.

Heribert Proepper/AP

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Global warming is taking a break that could last for another 10 years or so.

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That's the latest word from a team of climate researchers in Germany. Global average temperatures should remain above normal, the team suggests. But additional warming – already on hold over the first seven years of this decade – is likely to remain that way for another decade. The reason? The team says it expects natural shifts in ocean circulation to affect temperatures in ways that temporarily out-wrestle the effects of rising greenhouse-gas emissions.

The forecast is "very bold," cautions Tom Delworth, a scientist at the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory at Princeton University. But, he adds, it represents the cutting edge of climate modeling. The German effort is one of the first widely published attempts to offer climate forecasts on time scales of a decade or so, rather than a century or more. The findings appear in Thursday's edition of Nature

Even without global warming, decades-long natural shifts in climate can have big social and economic effects. These changes are thought to drive highs and lows in the average intensity of a string of hurricane seasons or the recurrence of persistent periods of drought, for instance. That alone makes the effort to forecast them worthwhile, researchers say. But these shorter-term climate forecasts also can act as a more immediate reality check on century-scale climate projections, since the same computer models are being used for both tasks. And they have the potential to identify more clearly those cases where global warming is responsible for triggering a decade's climate patterns, rather than natural variability.

"These are nice first steps," Dr. Delworth says of the efforts so far.

The latest attempt comes from climate modelers at the Leibniz Institute for Marine Sciences in Keil, Germany, and the Max Planck Institute for Meteorology in Hamburg. But they used their global model in a slightly unorthodox way.

Climate models are bursting with equations that describe physical processes taking place in and among ice and snow, the ocean, and atmosphere. Typically, scientists plug in a small handful of outside "forcing" conditions – the amount of light the sun emits as it undergoes its own cycles, as well as levels of man-made and natural greenhouse gases and tiny particles called aerosols. Then they let the model run. In the process, the model recreates natural variations. But until now, these variations have often been considered "noise" that interferes with teasing out global warming's long-term trajectory.

But the German team was looking to more finely model that noise to forecast climate change on much shorter time scales. To do that, they borrowed a page from weather forecasters, who plug in measurements from weather balloons, satellites, and other sensor platforms as a starting point for their computer calculations.