60秒科学:Why Didn't Earth Freeze Completely?（在线收听）

Why Didn't Earth Freeze Completely?
Research published in the July 2 issue of Nature reveals one reason our planet didn't succumb to an enveloping ice sheet during glacial ages. Christie Nicholson reports.

 [The following is an exact transcript of this podcast.]

During the last ice age our problem was too little carbon. Unlike today where too much carbon is causing global warming.

Past glacial ages occurred partly because the weathering of rocks, over millions of years, pulls CO2 from the atmosphere, locking it in ocean floor sediment. The rise of global mountain ranges during the last 25 million years should have sucked all the CO2, sending the Earth to an icy death.

But that never happened. CO2 levels stabilized at about 250 parts per million.

This week in the journal Nature, researchers announce one reason why this happened: plants.

Leafy greens need CO2 to live, and when CO2 levels drop significantly they starve. Researchers say that the plant numbers decreased to a level where volcanoes and other carbon-creating sources produced CO2 faster than the remaining plants could remove it. So the Earth remained somewhat warm.

It may seem that our leafy friends could help us now, this time from overheating. But ultimately we’re producing too much CO2 too fast for natural weathering processes to remove it. Ultimately, we need a way to stop producing CO2 in the first place.

—Christie Nicholson