nge of predicting global climate is immense. There are hundreds of variables, from the reflectivity of the earth's surface (high for icy spots, low for dark forests) to the vagaries of ocean currents. Dealing with these variables requires supercomputing capabilities. Computer power is so coveted by climate scientists that the U.S. Department of Energy gives out access to its most powerful machines as a prize.

The resulting simulations both map out the past and look into the future. Models of the ancient past can be matched with fossil data to check for reliability, making future predictions stronger. New variables, such as the effect of cloud cover on climate, can be explored. One model, created in 2008 at Brookhaven National Laboratory in New York, mapped the aerosol particles and turbulence of clouds to a resolution of 30 square feet. These maps will have to become much more detailed before researchers truly understand how clouds affect climate over time.

Building brains

So how do supercomputers stack up to human brains? Well, they're really good at computation: It would take 120 billion people with 120 billion calculators 50 years to do what the Sequoia supercomputer will be able to do in a day. But when it comes to the brain's ability to process information in parallel by doing many calculations simultaneously, even supercomputers lag behind. Dawn, a supercomputer at Lawrence Livermore National Laboratory, can simulate the brain power of a cat — but 100 to 1,000 times slower than a real cat brain.

Nonetheless, supercomputers are useful for modeling the nervous system. In 2006, researchers at the École Polytechnique Fédérale de Lausanne in Switzerland successfully simulated a 10,000-neuron chunk of a rat brain called a neocortical unit. With enough of these units, the scientists on this so-called "Blue Brain" project hope to eventually build a complete model of the human brain.

The brain would not be an artificial intelligence system, but rather a working neural circuit that researchers could use to understand brain function and test virtual psychiatric treatments. But Blue Brain could be even better than artificial intelligence, lead researcher Henry Markram told The Guardian newspaper in 2007: "If we build it right, it should speak."

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