How the big melt-off starts
When an ice age ends, which comes first: a rise in world temperature or an increase in greenhouse gases? After analyzing the carbon-dioxide content in tiny air bubbles trapped in Antarctic ice, then comparing the results with ancient temperature records, researchers from Scripps Institute of Oceanography in San Diego say the answer is temperature warming.
Warming, they report in Science magazine, is started by changes in Earth's position relative to the sun. This causes organisms to flourish and produce carbon dioxide through respiration and decay.