The signs are everywhere, scientists say. Our climate is changing. Global warming can't be blamed for every heat wave, drought or devastating storm pattern, but our best scientists believe our warming world will make extreme weather more common and more deadly.

President Bush's recent decision to abandon the 1997 Kyoto treaty to combat climate change came as a surprise since even the new administration admits global warming is a "serious" issue. The President's dismissal of nearly nine years of international negotiations sparked protests around the world, and caused trouble with some close allies such as German Chancellor Gerhard Schroder.

A decade ago, global warming was an idea that was largely theoretical. But a recent report by the U.N.-sponsored Intergovernmental Panel on Climate Change (IPCC) makes it clear that global warming has begun. Over the past century worldwide temperatures have climbed more that 1 degree F, and the 1990s were the hottest decade on record. The result is a laundry list of changes that scientists have recorded. For instance: the annual melt season in Antarctica has increased up to three weeks in just 20 years; the legendary Mount Kilimanjaro has lost 75 percent of its ice cap since 1912, and scientists believe it could vanish from Africa's tallest peak within 15 years; Venezuelan mountaintops had six glaciers in 1972, but only two remain; and all of the glaciers in Montana's Glacier National Park will disappear by 2070 if their retreat continues at the current rate.

Beyond melting snows and rising ocean levels, coral reefs are dying off as ocean waters grow warmer, and drought is the norm in parts of Asia and Africa. We've also seen the devastating effects of more frequent El Nino events on weather patterns in the United States.

Such facts have convinced scientists that global warming is no longer just theory. In fact, they say, temperatures may be rising faster than anyone expected. Since the start of the Industrial Revolution, humans have increased the concentration of carbon dioxide 30 percent, and each year the rate of increase grows faster. By 2100, the IPCC says, average temperatures will increase between 2.5 degrees F, and 10.4 degrees F. That's more than 50 percent higher than predictions made just six years ago.

Even lower-end estimates of temperature change could cause severe problems for agriculture. Droughts would be more common and ecosystems would be thrown out of balance. If the temperature rise is in the upper end of estimates, the result would be disastrous. Entire climatic zones might shift, leaving areas like central Canada looking more like central Illinois. Agriculture could be thrown into turmoil.

Given such a gloomy forecast, it's understandable that many foreign leaders were upset with President Bush when he announced in March that he was abandoning his campaign pledge to curb carbon dioxide emissions from power plants. And when he rejected the Kyoto treaty, global reaction was furious. Many call it reckless, since the United States has just 4 percent of the world's population, yet produces 25 percent of its greenhouse gases.

Fighting global warming is a long-term project, and a battle that can't be won without the help of the U.S. President Bush's reluctance to support the effort can do significant harm to the global climate over the next century, and can harm the ability of your grandchildren to survive as farmers and ranchers.