The effect of adding carbon dioxide and other greenhouse gases to the atmosphere is well known. Less well known is the effect of deforestation. The removal of trees that efficiently absorb sunlight, exposes bare ground that reflects back into space much more of the incident sunlight than the canopy of a forest, and which, as it is heated by the sun, emits much of the absorbed heat to outer space as infra-red radiation.
Trees, in contrast, don't heat up much in the sun: they cool by evaporation of transpired water. In the process, solar energy is converted to the latent heat of vaporization, which warms the atmosphere when the water vapor lost by trees condenses to form clouds. The clouds may reflect sunlight, but they also reflect infra-red radiation emitted from the ground that would otherwise have escaped to outer space. Trees, in other words, may contribute to global warming, though as repositories of carbon they also counteract warming. Overall their effect on global temperature is probably positive. Then they emit hydrocarbon pollutants too — an estimated 30 million tons per year in the US, alone.
Then there are sulfur emissions from coal fired power plants, which give rise to white sulfate particles that cool the atmosphere by reflecting sunlight; and the production of black carbon particles (soot) during the combustion of diesel and heavy oil, which absorb sunlight and thus warm the atmosphere.
So it's complicated, which is why it takes a supercomputer to model the climate, and why the validity of the results obtained are always open to question.
But despite the unending debate, and the endless muddying of the waters by partisans, politicians and boobs on both sides of the argument, most if not all informed global warming skeptics appear to acknowledge that raising atmospheric carbon dioxide concentration as we are currently doing will likely raise global temperature by the end of the present century significantly above what it would otherwise have been.
What well-informed skeptics are in most cases skeptical about is not the likelihood of human-caused global warming but the magnitude of the effect as predicted by the so-called warmists, and the necessity of taking drastic or enormously costly actions to prevent the warming that will occur without major efforts at mitigation.
Christopher Monckton, who served as an adviser to UK Prime Minister Margaret Thatcher, is a skillful debater and a fair mathematician who has followed the climate change debate, and has participated vigorously in it for years, is undoubtedly a climate warming skeptic. So whatever warming he agrees has occurred and is likely to occur in the future should atmospheric carbon dioxide continue rising on its present course might be considered a lower bound for the warming that virtually all the experts, skeptic or warmist, say we can expect (all other things being equal, which they almost certainly will not be).
It is convenient, therefore, that Christopher Monckton has just published an estimate of the rate of warming over recent and future decades. This estimate is contained in a post on Alan Watts blog from which the following is an excerpt.
I have had the pleasure of being on the planet for 60 years. I arrived when it first became theoretically possible for our CO2 emissions to have a detectable effect on global temperature. From 1952 to the present, the planet has warmed at a rate equivalent to 1.2 Celsius degrees per century. ...Whether Christopher Monckton's estimate is closer to the truth than that of the University of East Anglia, I will not venture to say. But what Monckton makes clear is that rational people on the skeptic side of the climate warming debate do expect climate warming in the century and a half beginning 60 years ago, of around 2 degrees Celcius, assuming that atmospheric carbon dioxide concentration continues rising on its present course.
Late in 2001 there was a phase-transition from the warming to the cooling phase of the Pacific Decadal Oscillation, the most influential of the ocean oscillations. From 1990-2001 is 11 years; from 2001-2012 is 11 years. So 1990-2012 is a period centered on a phase-transition: with minimal natural distortion, it will indicate the recent temperature trend.
Since 1990 the world has warmed at 1.4 Cº, century, or a little under 0.3 Cº in all. Note that 1.4 Cº/century is a little greater than the 1.2 Cº/century observed since 1952. However, the period since 1990 is little more than a third of the period since 1952, and shorter periods are liable to exhibit somewhat steeper trends than longer periods.
So the slightly higher warming rate of the more recent period does not necessarily indicate that the warming rate is rising, and it is certainly not rising dangerously.
For the 21st century as a whole, IPeCaC is predicting not 1.2 or 1.4 Cº warming but close to 3 Cº, more than doubling the observed post-1990 warming rate. Or, if you believe the latest scare paper from our old fiends the University of East Anglia, up to 6 Cº, quadrupling it.
Two degrees is the difference in temperature between London and Edinburgh, or between London and Paris. Such a change can hardly be called catastrophic, and for some people, the Scotch for example, it will surely be of huge benefit. But for others, there will undoubtedly be a downside, especially where a change in temperature is associated with a reduction in rainfall and soil water. The viability of the Canadian prairies as grain growing region, for example, could be radically affected.
Thus it seems only sensible to consider measures to limit greenhouse gas emissions and atmospheric release of other greenhouse gases. In the case of carbon dioxide emissions, these can be limited easily and efficiently by means of a carbon tax. All governments need revenue. They might as well tax something we don't want, including the causes of climate warming, while easing up on taxes on such things as income, that we do want.
The objection energy intensive industries in countries with a carbon tax are placed at a disadvantage in competition with competitors in countries without a carbon tax, can be disposed of by the imposition of countervailing duties on goods from countries that do not impose a carbon tax. If the US or the EU were to institute a carbon tax on that basis, the rest of the World would be compelled to follow.