To: Sam who wrote (7544 ) 4/24/2009 10:34:51 PM From: Brumar89 Respond to Positive and negative feedbacks are always possible positive feedbacks. negative feedbacks won't happen, they will. are the net feedbacks from increased CO2 positive on balance or negative on balance? During the 1990s, further ice core measurements indicated that during past glacial periods, temperature changes had preceded CO2 changes by several centuries. Was it necessary to give up the simple hypothesis that had attracted scientists ever since Tyndall in the 19th century — that changes in CO2 were a simple and direct cause of ice ages? Some scientists doubted that dates could be measured so precisely, but most of the evidence pointed to a time lag.(54) This confused many people. If changes in CO2 lagged behind changes in temperature (and likewise for methane, another greenhouse gas measured in the ice cores), didn’t that contradict the greenhouse theory of global warming? But in fact the lag was not good news. a powerful feedback cycle was amplifying the effect of the cyclical changes in sunlight. Even a small change in the gas level would bring further changes in the global heat balance, which would in turn alter the gas level, which... and so forth. Or, more ominously, how a change in the gas level initiated by humanity might be amplified through a temperature feedback loop. The ancient ice ages were the reverse of our current situation, where humanity was initiating the change by adding greenhouse gases. As the gas level rose, temperature would rise with a time lag — although only a few decades, not centuries, for the rates of change were now enormously faster than the orbital shifts that brought ice ages. In the network of feedbacks that made up the climate system, CO2 was a main driving force.
