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A. A Fingerprint of Human Effects on Global Climate

Narrator: This is Science Today. By studying climate model experiments, scientists at the Lawrence Livermore National Laboratory have discovered another fingerprint of human effects on global climate. Lab scientist Ben Santer says they found that in the last two decades, increases in the height of the tropopause - a transition zone between the upper and lower atmospheres - are linked to ozone depletion and an increase in greenhouse gases.

Santer: There's still uncertainty about the global scale's sign of the change in tropospheric temperatures. Our work suggests that the troposphere may well have warmed and without that warming you couldn't really get this pronounced increase in tropopause height.

Narrator: This is the first time scientists examined whether observed changes in tropopause height corresponded with projections from climate model experiments on greenhouse warming.

Santer: If the models are even in the ballpark, then we can expect some large changes in climate over the next century and it behooves us to try and understand those changes.

Narrator: For Science Today, I'm Larissa Branin.