1. The climate is never just "average"; it changes all the time, from season to season, year to year, and over the millennia. And that includes not only temperature, but rain, snow, droughts, storms, and every conceivable feature of the weather. So watch out when you read about the "hottest year", "longest drought", or "biggest hurricane".

2. Is it getting warmer or is it getting colder? The correct answer is: Yes. It all depends on the time scale you choose. The global climate has warmed over the last 100 years, but not appreciably over the last 50 years. And it is colder now than it was 1000 years ago. And did you know that over the last 50 years the frequency of hurricanes has been dropping?

3. Are human activities influencing climate? Yes, of course. The rise of agriculture and the growth of cities have changed the local climate significantly. With rising populations and rising industrial activity there have also been some worldwide changes: Temperature extremes have softened, the stratosphere is cooling, the frequency of hurricanes has been diminishing -- all of these are thought to be human influences on the atmosphere. But this does not mean that there will be a catastrophic or even a substantial warming of the climate in the next century.

4. Isn't there climate warming already because of the increased burning of fossil fuels -- oil, gas, and coal -- that creates more carbon dioxide in the atmosphere? True, carbon dioxide (CO₂) levels are rising, but the climate seems not to be warming. It did warm greatly between 1880 and 1940 -- long before CO₂ increased significantly. But since 1940, weather satellites, tree ring data, and corrected thermometer readings all agree that climate has not warmed -- even though CO2 levels rose.

5. Why hasn't climate warmed, when theory clearly expects this to happen? The answer must be that even our best current models of the atmosphere are incomplete and leave out important features. Only in the last few years have modelers started to include ocean currents, atmospheric aerosol particles and dust into climate models. Most now suspect that clouds are the reason why models and observations do not agree.

6. What about climate calamities, like sea-level rise and the spread of tropical diseases? Well, since the climate is not warming, there is no immediate reason for concern. Diseases are not just spread by mosquitoes, but nowadays more by human contacts -- which have been increasing markedly with the tremendous rise in global transportation. Many scientists predict that sea level will drop if oceans warm; the evaporated moisture may simply turn to snow and increase the thickness of the Greenland and Antarctic ice caps.

7. Would a global warming be good or bad? Probably both, but warming is definitely better than cooling. It is certainly better for agriculture and therefore for basic human existence. All historical evidence shows that during the warm periods of the Middle Ages people were better off than during the hard times of the "Little Ice Age" (1650-1850) when crops failed and people starved.

8. What can we do about climate warming? We can do little about the climate itself, but we could try to stop the increase of atmospheric CO2. Even that task is daunting; it requires that we cut emissions -- worldwide -- by 60 to 80 percent. In effect, this means cutting energy consumption by comparable amounts -- including all transportation, heating, air conditioning, and electricity use. It would have an enormous negative impact on people's welfare -- particularly for the poor and those in developing countries.

9. How would one reduce energy consumption by 60 to 80 percent? There are basically two ways, short of drastically reducing population itself: energy rationing or energy taxes. Rationing means a political allocation, with governments and bureaucrats deciding who may use energy and who may not. Energy taxes are almost as unpalatable; just try to picture $3-per-gallon gasoline.

10. Should we ruin our economies and cause tremendous hardship for people to counter a phantom threat? That's a leading question; climate warming does indeed seem far away and a minor problem at that. There is a sure threat to human existence, however, and that is the near-certainty of a coming ice age. Geologists tell us that the present interglacial warm period will soon come to an end. Perhaps greenhouse warming can save us from an icy fate.



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