I DON'T KNOW, BUT DO SOMETHING

Ice ages key to understanding change (Fred Pearce, 8/26/2003, Boston Globe)

We know about past levels of greenhouse gases in the atmosphere because researchers have been able to recover bubbles of ancient air trapped in ice. These bubbles reveal past temperatures and concentrations of gases in the air. They show that when the world was at its coldest, carbon dioxide levels in the air were low; and when it got warmer, they rose.

But they reveal something more startling. The changes between these two situations were not smooth and gradual. They were extremely quick. It is almost, Watson said, as if the planet has a rather crude thermostat, with just two settings -- ice age, and not ice age.

Put another way, there appear to have been two "stable states" for the planet's climate system. Once one of them broke down, the entire system switched within a few centuries to the other. [...]

None of this is proved. But whatever the precise mechanism, Watson said, we are left with the worrying fact that, in the past 2 million years or so, the world had two stable climatic states -- anchored at 190 ppm and 280 ppm of carbon dioxide. Why worrying? Because, Watson said, we have now slipped the anchors. By burning fossil fuels, we have forced up carbon dioxide levels to 370 ppm today. That is probably higher than for millions of years. And the level is still rising by almost 20 ppm a decade.

The question now is: How will the planet respond? Until now, climate scientists have mostly expected that a gradual rise in greenhouse gases will cause a gradual increase in temperatures. Now there are two other possibilities. The planet might find a way to keep temperatures down. Or it might make another jump -- to perhaps a third "stable state" about which we as yet know nothing.

How might that happen? Peter Cox of the British government's meteorological service, said that within 50 years, rainforests and their soils could begin to dry out and die as warming gathers pace. That would release carbon dioxide into the atmosphere and accelerate warming. Others predict changes in the ocean circulation systems that reduce the oceans' abilities to absorb carbon dioxide from the air.

Nothing is certain in this. Climate scientists are being forced to acknowledge how little they know about how the planet works. But that ignorance, they say, should make us more worried rather than less.

The willingness of scientists to recommend radical courses of action despite "how little they know" is far more worrisome than the lack of knowledge itself. Posted by Orrin Judd at August 30, 2003 6:56 AM