Short answer: No!
Long answer [discussing the first Cockburn screed you linked to]:
Cockburn (paraphrasing): How come the 30% drop in human emissions of CO2 at the time of the Great Depression didn’t show up in the atmospheric levels of CO2? Doesn’t this show the rise in CO2 levels isn’t being produced by our burning of fossil fuels?
Answer: First of all, Cockburn is confusing a drop in the rate of increase and a drop in a level…not the same thing. I.e., the 30% drop in emissions shouldn’t lead to a drop in CO2 levels but rather to a drop in the rate of growth of CO2 levels. Second, Cockburn is taking the data way further than it can be taken. As he notes, measurements of sufficient time-resolution to detect, for example, the seasonal cycle in CO2 levels were not available before 1958. What the pre-1958 measurements rely on is bubbles captured in glacial ice and since these bubbles take a long time to close off, they don’t provide the sort of temporal resolution Cockburn desires. Third, we know that there are various sources of variability in the rise in CO2…i.e., the amount in the atmosphere increases by about 1/2 of what we put into the atmosphere every year but the percentage is not exact. This is not surprising given that there are some large fluxes of CO2 between the atmosphere and oceans and biosphere that are influenced by various factors. However, just because these introduce “noise” into the system does not mean that we are not responsible for the long-term trend of rising CO2 levels. In fact, it is known with such confidence that we are that even very few of the skeptics argue this point anymore; Cockburn is way out in the field on this one. (For example, the “Greening Earth Society” was so-named because they were trying to argue that the rise in CO2 levels was a blessing that we were giving the earth because it would promote plant growth.)
Cockburn: Water vapor is a greenhouse gas found in much higher concentrations than CO2 and thus CO2 concentration is irrelevant. “And water is exactly that component of the earth’s heat balance that the global warming computer models fail to account for.”
Answer: Yes, water vapor contributes more to the natural greenhouse effect than CO2. However, the natural greenhouse effect warms the earth by a very large ~30C, and the contribution due to CO2 is not insignificant. And, because radiative forcing depends approximately logarithmically on the concentrations of each of the greenhouse gases, what is relevant is the fractional change in the levels that you are causing. We have already cause a significant fractional change in CO2 concentrations (+35%) and will be hard pressed not to more than double CO2 concentrations from pre-industrial levels by the end of the century. Furthermore, the computer models do in fact account for water vapor. In fact, there is a positive feedback whereby the warming due to CO2 causes increased evaporation and therefore an increase in water vapor concentration, which causes further warming. This effect roughly doubles the warming due to CO2 alone. This is not to say that the models deal with water vapor perfectly…there are still difficulties in particular with the way clouds are handled by the models. However, various checks have been made against real data to give confidence that the models are handling the water vapor feedback effect roughly correctly.
Cockburn: “It’s a notorious inconvenience for the Greenhousers that data also show carbon dioxide concentrations from the Eocene period, 20 million years before Henry Ford trundled his first model T out of the shop, 300-400 per cent higher than current concentrations.”
Answer: It is not an inconvenience at all. Saying that we are responsible for the current rise in CO2 levels does not exclude other causes for rises in CO2 on much longer timescales over the earth’s geological history. (After all, where does he think all the carbon locked away in the fossil fuels got there in the first place?!) In fact, there is an increasing ability to model the carbon cycle and show rises and fall of CO2 levels on these sorts of very long geological timescales. However, the fact remains that over at least the least ~7 glacial / interglacial cycles going back ~750,000 years, CO2 levels were always between about 180ppm and 300ppm whereas in the last ~150 years they have risen from 280ppm to 380ppm! In fact, one likely does have to go back close to 20 million years to find levels of CO2 higher than current levels!
Cockburn: “The Greenhousers deal with other difficulties like the medieval warming period’s higher-than-today’s temperatures by straightforward chicanery, misrepresenting tree-ring data (themselves an unreliable guide) and claiming the warming was a local, insignificant European affair.”
Answer: Well, it is true that temperature reconstructions using tree ring and other data are not perfect. However, when you look at the evidence from sites around the world (well, mainly around the Northern Hemisphere since Southern Hemisphere data is sparse), one sees that, while many places experienced some warmth during a several hundred year period broadly defined as the Medieval warming period, the warming in different areas tended to be asynchronous. So, when you average it all together, the overall warming you see in the Northern Hemisphere during this period is rather weak and it does not appear to have ever gotten as warm as it has in the last half of the 20th century.
Cockburn: “We’re warmer now, because today’s world is in the thaw following the last Ice Age. Ice ages correlate with changes in the solar heat we receive, all due to predictable changes in the earth’s elliptic orbit round the sun, and in the earth’s tilt. As Hertzberg explains, the cyclical heat effect of all of these variables was worked out in great detail between 1915 and 1940 by the Serbian physicist, Milutin Milankovitch, one of the giants of 20th-century astrophysics. In past postglacial cycles, as now, the earth’s orbit and tilt gives us more and longer summer days between the equinoxes.”
Answer: Well, the last Ice Age (or “glacial period”) ended about 12,000 years ago. In fact, the seminal paper from the mid-1970s that argued for the Milankovitch cycles being the pacemaker for the ice ages argued that the long-term natural trend on the basis of these cycles over the next 20,000 years should be toward glaciation (although some scientists now argue that this current interglacial would have lasted longer than that…maybe another 40,000 to 50,000 years even without our intervention). Furthermore, the rate of rise in temperature coming out of the last ice age averaged about 0.1-0.2 C per century over a period of a few thousand years. By contrast, our current rate of warming over the last 35 years has been close to 0.2 C per decade. Finally, the ice ages, far from disproving the AGW theory, actually provide support for it. E.g., by estimating the radiative forcings and the resulting warming that occurred, Jim Hansen has come up with an estimate of the climate sensitivity to the known forcing due to increasing CO2 levels. This estimated sensitivity is in good agreement with that estimated by climate models (albeit with reasonable-size error bars for both estimates).
Cockburn: “Water covers 71 per cent of the surface of the planet. As compared to the atmosphere, there’s at least a hundred times more CO2 in the oceans, dissolved as carbonate. As the postglacial thaw progresses the oceans warm up, and some of the dissolved carbon emits into the atmosphere, just like fizz in soda water taken out of the fridge. ‘So the greenhouse global warming theory has it ass backwards,’ Hertzberg concludes. ‘It is the warming of the earth that is causing the increase of carbon dioxide and not the reverse.’ He has recently had vivid confirmation of that conclusion. Several new papers show that for the last three quarter million years CO2 changes always lag global temperatures by 800 to 2,600 years.”
Answer: Actually, this last fact is hardly new news…In fact, the latest paper that I know of was one that suggested that the 800 year lag is possibly an artifact, although this has been greeted rather skeptically by the community since the 800 year lag makes sense. (The larger lag of ~2600 years upon cooling into ice ages has been demonstrated to be largely an artifact.) But the overall point is that, yes, in past climate changes before we were around to pump prodigious amounts of CO2 rapidly into the atmosphere, it is believed that warming due to the Milankovitch cycles and the associated decrease in glaciation then caused an increase in CO2 levels (released from the oceans and possibly also from the biosphere) which then further amplified the warming. However, the level of CO2 didn’t go above 300ppm, the rise in CO2 levels took hundred of years (as Cockburn’s lag time suggests), and the amount of CO2 rise wasn’t nearly as large for the same amount of warming as we have seen over the last century or so. Furthermore, we know that this time is different: We know that we are pumping CO2 into the atmosphere and that the oceans, far from releasing it, are actually acting as a sink of CO2, which is part of the reason why the atmospheric levels of CO2 are only rising about 1/2 as fast as they would be if all the CO2 we released remained there. (The biosphere is absorbing some too.) It is also why the oceans are becoming more acidic, more evidence that they are absorbing more CO2 than they are releasing. (However, Cockburn is right in one sense in that the warming of the oceans is expected to decrease their ability to act as a sink of our CO2 emissions.)
Cockburn: “…that’s not even to mention the role of the giant reactor beneath our feet: the earth’s increasingly hot molten core.”
Answer: It is good he didn’t mention it since the contribution of this to the heating of the atmosphere is utterly inconsequential (by several orders of magnitude) compared to the energy we absorb from the sun or even the change in the amount that we absorb due to the change in greenhouse gas levels.
