A colleague of mine at Northern recently expressed to me some doubt about the widely circulated claim that human activity is contributing to global warming, a claim with which I agree. It was a good question. How exactly do we know that human industrial output (in terms of green house gases) is responsible for the current global warming trend, and not, for example, other natural forces. Since the world has frequently been much warmer than it is now, and much colder, why assume that we have anything to do with current global climate trends?
Anyone who, like myself, is curious about global warming but is altogether an amateur when it comes to climate science, would do well to read Kerry Emanuel's lead article in the current Boston Review On-line. Emanuel is Professor of Meteorology at MIT, and an expert in the science of hurricanes. He is no doubter when it comes to global warming, but neither is he an hysterical Al Gore. He careful distinguishes confidence from uncertainty in the science.
He gives a chart that neatly answers my colleague's question.
The bluish shading represents models of natural influences of climate change: solar radiation and volcanic activity which, I gather, is a cooling factor. The pinkish shading represents models including the natural influences and the anthropogenic, or human influences, including the production of greenhouse gases along with human activity that mitigates warming. The black line represents actual observations, and it corresponds neatly with the natural + human influence model.
This, in a nutshell, is why almost all climate scientists today believe that man’s influence on climate has emerged from the background noise of natural variability.
In other words, what we actually observe when tracking climate change confirms the view that human activity is rapidly accelerating global warming.
Unlike climate expert Al Gore, Kerry Emanuel is honest and straight forward on the uncertainties in the science, and they are great indeed. But he convinces me, at least, that the general conclusion about human influences is sound.
What is very uncertain is whether all of this is bad news or not.
Projections based on climate models suggest that the globe will continue to warm another 3 to 7°F over the next century. This is similar to the temperature change one could experience by moving, say, from Boston to Philadelphia. Moreover, the warming of already hot regions—the tropics—is expected to be somewhat less, while the warming of cold regions like the arctic is projected to be more, a signal already discernable in global temperature measurements. Nighttime temperatures are increasing more rapidly than daytime warmth.
Is this really so bad? In all the negative publicity about global warming, it is easy to overlook the benefits: It will take less energy to heat buildings, previously infertile lands of high latitudes will start producing crops, and there will be less suffering from debilitating cold waves. Increased CO2 might also make crops grow faster. On the down side, there will be more frequent and more intense heat waves, air conditioning costs will rise, and previously fertile areas in the subtropics may become unarable. Sure, there will be winners and losers, but will the world really suffer in the net? Even if the changes we are bringing about are larger than the globe has experienced in the last few thousand years, they still do not amount to the big natural swings between ice ages and interglacial periods, and the earth and indeed human beings survived these.
Consider that increases in nighttime temperatures without much increase in daytime temperatures means longer growing seasons with less evaporation. You'd have to be a farmer to see bad news in that.
I think it very unlikely that we can halt the increase in greenhouse gases in the near term. That doesn't mean we shouldn't try, but trying will require such technologies as nuclear power. Mostly what we have to do is prepare for more warming. I am not yet much worried about this, but I live a long way from the beach.
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