Scientists do not dispute the fact that plant life thrives on carbon dioxide. What they disagree about is how much is too much. Many believe that the amount of CO 2 and other greenhouse gases that humans are adding to the atmosphere go far beyond what the planet can handle. This is the viewpoint of Dr. Tom Wigley, a climatologist and senior scientist with the National Center for Atmospheric Research. He acknowledges that not all global warming is harmful nor is an increase in CO 2 necessarily bad, because carbon dioxide accelerates plant growth. Wigley explains what does concern him: "What we're afraid of is that if the planet warms too much, we're going into unknown territory. We can't predict the climate well enough to know what to expect. So we certainly don't want to go too far down the road, down the pathway of global warming. We have time to think about what to do. But eventually, we have to do something dramatic." 36
Tom Crowley, a climate researcher in the oceanography department at Texas A&M, is another scientist who is concerned about the earth's future because so much is still unknown. There was a time when he was doubtful about the existence of global warming but that time has passed, as he explains: "To me the question of whether global warming is happening is receding as the central question. In my view, it's already here—and I didn't believe that two years ago. Now the question is: How will it affect us?" 37