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Dear Tom,
Global warming is always in the news. What is the real story?
Rod Belonvich, Chicago

Dear Rod,
Global warming is a vastly complex subject that does not lend itself to quick conclusions or to satisfying answers. The Earth has experienced natural warming and cooling trends all through its 4.5 billion years. Even within the last few hundred thousand years, the global climate has been warmer and cooler than it is at present. Right now, the Earth is pulling out of an ice age that reached a maximum about 10,000 years ago and temperatures have been rising irregularly since then. Man’s activities, especially those that add carbon dioxide to the atmosphere, are accelerating the warming trend. However, the rate of warming and the ultimate global consequences are still unresolved.