Some of the basics

Climatologists around the world agree on some important points: the climate has been warming and continues to warm, human activities (mostly fossil-fuel burning) have increased the level of CO₂ in the atmosphere from about 280 parts per million to almost 390 parts per million, and this ongoing increase in CO₂ causes the earth to retain more of the sun’s warmth. Climatologists can’t explain the recent warming trend without including the effects of this increase in CO₂ (and the resulting increase in water vapour, which evaporates as temperature increases, and amplifies the CO₂ effect). In particular, observations show there has been no significant increase in solar activity. Glaciers and ice caps are in retreat—and, though they have retreated before, the slow orbital changes that have driven those cycles in the past aren’t at work this time. Further, the fact that those orbital changes could drive those cycles depends on a small signal- a slight increase in sunlight in the northern hemisphere- being amplified by the earth’s climate system. CO₂ increase is also small signal- but it’s growing rapidly, and the same processes that turned a slight increase in northern sunlight into the end of the last ice age are already amplifying that small signal.

But many people refuse to take global warming seriously. Rex Murphy recently compared those who argue against global warming to Galileo, likening the vast majority of climate scientists to the dogmatic religious defenders of Ptolemy’s earth-centered astronomy.

Sorry, Rex, but Galileo—a brilliant satirist—would have made mincemeat of you and your denialist crew. It’s true that scientists sometimes get things wrong, but the clerics and dogmatists who opposed Galileo were bent on asserting the church’s authority over science, not defending a scientific consensus. A better example for Rex's purposes would be Newton’s mechanics: for a long while, the best scientific minds thought mechanics was the final word on physics, but now we know that quantum mechanics is needed to understand many phenomena. But even this isn’t much help to Rex. Newton’s mechanics still works as well as ever—it’s still reliable for its former applications and for many more that scientists continue to develop. It’s not the final word in physics, but it’s still effective and reliable.

Rex and other skeptics claim that our inability to predict the weather more than a few days in advance demonstrates just how absurd it is to make predictions about the climate many years from now. But this is just wrong (Wolfgang Pauli would have said it's not even wrong). Climate is average weather, and averages are much easier to predict than the individual events they are averages of. I can’t predict how many games the Flames will win this year, but I can easily predict the average proportion of games that NHL teams will win: 50%. After all, on the present rules every game has a winner (and a loser).

Climate scientists understand the basic processes that drive the earth’s climate—how the light from the passes through the atmosphere, warming the air and the surface, how that energy moves around in the atmosphere and from the atmosphere to the oceans, through convection, winds and currents, and how energy is finally radiated, at lower frequencies, back up through the atmosphere and into space. Carbon dioxide is an important factor in this last process: it absorbs some important frequencies of infrared light, capturing some of the radiation from the surface and warming the air. Some details have to be added based on observations and known correlations, since we can’t solve the fundamental equations across all the scales, ranging from a few meters to thousands of kilometers. But the models that result are very successful.

Today’s climate models use these processes to predict a wide range of features of the climate, including seasonality, large-scale wind patterns , the distribution of surface temperatures and the higher rate of global warming in the arctic, along with the higher intensity of the winds that surround Antarctica and delay global warming in the colder parts of that continent. None of these models can be tweaked to explain the observed warming since the mid-twentieth century without the effect of increased carbon dioxide. (And, by this way, this increase does really come from the fossil fuels we burn—among other things, the depletion of carbon 14 in the atmosphere proves the additional carbon is old, i.e. fossil carbon.)

Could the scientists just be wrong anyway? Yes, they could. But ignoring their warnings is a huge risk. Agriculture, in particular, depends on the weather averaging out over the years. A significant change in the average could easily disrupt food supplies, destabilizing poorer countries and triggering massive, desperate migrations of hungry people. The Pentagon believes climate change could lead to serious security threats even for the United States—with a military that spends about as much as the rest of the world’s military budgets combined. Even if all we can do is slow the changes and prevent a massive shift in climate (one we couldn’t reverse over the coming centuries), the gains of reducing and delaying any crises is almost certain to be worth the price we pay in some reduction in economic growth. Our grandchildren will thank us—instead of remembering us as selfish fools who played chicken with the planet we all depend on.

UPDATE: For a vigourous response to the Climategate spin, see http://desmogblog.com/elizabeth-may-informed-look-east-anglia-emails

Note: This is a slightly extended version of an article first published in the Lethbridge Herald on Friday, November 13. I thank to the Herald for permission to re-publish material from that article.