Get used to it. The weather may feel like science fiction, but the science underlying it is very real and mundane. It takes only a small increase in global average temperatures to have a big effect on weather, because what drives the winds and their circulation patterns on the surface of the earth are differences in temperature. So when you start to change the average surface temperature of the earth, you change the wind patterns-and then before you know it, you change the monsoons. When the earth gets warmer, you also change rates of evaporation-which is a key reason we will get more intense rainstorms in some places and hotter dry spells and longer droughts in others. How can we have both wetter and drier extremes at the same time? As we get rising global average temperatures and the earth gets warmer, it will trigger more evaporation from the soil. So regions that are already naturally dry will tend to get drier. At the same time, higher rates of evaporation, because of global warming, will put more water vapor into the atmosphere, and so areas that are either near large bodies of water or in places where atmospheric dynamics already favor higher rates of precipitation will tend to get wetter. We know one thing about the hydrologic cycle: What moisture goes up must come down, and where more moisture goes up, more will come down. Total global precipitation will probably increase, and the amount that will come down in any one storm is expected to increase as well-which will increase flooding and gully washers. That's why this rather gentle term "global warming" doesn't capture the disruptive potential of what lies ahead. "The popular term 'global warming' is a misnomer," says John Holdren. "It implies something uniform, gradual, mainly about temperature, and quite possibly benign. What is happening to global climate is none of those. It is uneven geographically. It is rapid compared to ordinary historic rates of climatic change, as well as rapid compared to the adjustment times of ecosystems and human society. It is affecting a wide array of critically important climatic phenomena besides temperature, including precipitation, humidity, soil moisture, atmospheric circulation patterns, storms, snow and ice cover, and ocean currents and upwellings. And its effects on human well-being are and undoubtedly will remain far more negative than positive. A more accurate, albeit more cumbersome, label than 'global warming' is 'global climatic disruption.'
( Thomas L. Friedman )
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