Thursday, July 20, 2006

Ask now the beasts, and they shall teach thee...

Here is a short notice in Nature of two papers to be published this month in Science.
Climate science: Poles apart

Help may be at hand for climate scientists struggling to explain dramatic shifts in Earth's past ice cover.

The periods of glaciation that began around 3 million years ago come and go on a 40,000-year cycle, which clearly follows changes in Earth's tilt towards the Sun. What puzzled scientists was the lack of evidence for a cycle tracking the planet's proximity to the Sun during summer, which varies over a 20,000-year period. These properties of the Earth and its orbit affect the amount of sunshine reaching Earth's surface, which in turn influences ice cover.

Maureen Raymo of Boston University and her colleagues argue that the proximity effect is canceled out in the sea-level records used to track glaciation because changes in ice volume at the South Pole are equal and opposite to those at the North Pole. In a separate study, Peter Huybers of Harvard University in Cambridge, Massachusetts, suggests instead that proximity is simply canceled by speed: when Earth is close to the Sun, it moves faster, so a hot summer is also a short one.

The two hypotheses have different implications for global climate; further data might determine which effect is the greater.
One of the long-standing mysteries of paleoclimatology, two proposed solutions. Both solutions with sufficient empirical support to get past peer review. Which will prevail? Time will tell. Already researchers are considering whether the two theories make different predictions about other aspects of climate that can be tested empirically. The answer may lie in ancient air bubbles trapped deep in Antarctic ice or in isotope ratios of deep ocean sediments. Query nature. That's what science is all about.