I have put a question mark at the end of the title, since that sentence, made as a statement is highly controversial. Indeed, the term "denier" has been accoladed to the still substantial faction, including some serious and respected scientists, who challenge the assertion, based on computer models of the earth's climate that the increase in atmospheric CO2 derived from fossil fuel carbon is causing the planet to warm-up, perhaps by an additional 5 - 6 degrees C by 2100.
Let me emphasise my own perspective here. I am not a climatologist, but I do see that the most immediate impact on human life on earth will be caused by the dearth of cheap oil, then gas, and finally coal. Unless fast-breeder reactors, including thorium-based systems (the simpler liquid fluoride reactors rather than the vastly complex accelerator driven systems) are introduced fast and on a large scale, or other deposits of uranium are found, nuclear too will overrun its energy supply within 40 - 50 years, or sooner if nuclear power is proliferated as most western governments aspire to do.
If the climate models are correct in their predictions, the impact of carbon emissions will be felt later than that, and it is debatable how much we can moderate this, simply by reduced carbon emissions strategies (see yesterday's posting). Once we begin to eliminate fossil fuels, either through new "clean" technologies or by simply running out of them, the anthropogenic burden of CO2 will begin to level off. However, if the oceans are becoming saturated with CO2 in the surface layers and are less able to dissolve more of the gas, the consequences of carbon emissions both past and future may haunt us for millennia.
Since various computer models give different answers, e.g. warming by as little as 1 degree or as much as 5 degrees by the end of the century, it would be handy to have some experimental data to make recourse to. Obviously, we can't know the future, and that will only unfold as time passes. However, there is the geological record which gives some clues as to past behaviour. In a nutshell, according to ice-core samples, rather than the CO2 increasing and then the earth heating up, what may be deduced is the reverse of this; i.e. the planet warms and then, with a lag of around 800 years, the CO2 levels increase in the atmosphere.
The observables are a little less direct than this, since the temperature at a particular time in history is deduced from the ratio of heavy (deuterium) to light (protium) hydrogen isotopes (and O-18/O-16) in water (ice-cores), i.e. the ratio of heavy water to (ordinary) light water. Since the heavy water tends to evaporate more when it is hot, an increase in the heavy/light water ratio is observed, and vice versa for cold periods. There has been some speculation as to the accuracy of such isotopic thermometers, and corrections are proposed that close the gap somewhat between the temperature and CO2 levels suggesting a closer correspondence between the two, but nonetheless the initial heating period cannot be explained as being caused by rising CO2 levels, even though it may well be that once the CO2 concentration increases, its heat-trapping effect does introduce a thermal feedback to the climate.
One might speculate what exactly is the mechanism for that initial warming process if it cannot be simply explained in terms of CO2. Possibly, Milankovich cycles (changes in the amount of solar energy received by the Earth according to changes in the periodicity of its orbit over time) may play some role. For example, the roughly 100,000 year period between ice-ages corresponds to an "orbital forcing factor", between the closest and most distant approach of the Earth to the Sun, following the slightly undulating ellipse of its solar-orbit.
Some recent papers provide evidence that the global climate is subject to variation even over the past few centuries, i.e. before humans began burning up to the present 7 billion tonnes of carbon fuels each year. Global temperatures declined abruptly by around 2 degrees C from the Medieval warm period (1200 AD to 1500 AD) to the little ice-age (1500 AD to 1850 AD), when skaters built fires to roast chestnuts on the frozen surface of the river Thames in London. More detrimentally, there were widespread and frequent crop failures during the latter cold period which led to perhaps a million deaths from famine and disease. After 1850, average temperatures rose by around 4 degrees C, and this was before humans began releasing huge amounts of CO2 into the air. This amount of global warming was about 7 times the temperature increase observed during the past century and cannot be attributed to CO2 emissions since the CO2 levels in the atmosphere were relatively low then.
Since 1977, both the Earth mean temperature and the atmospheric CO2 levels have increased, which is usually taken as causative of the former, and yet during the 30 years prior to then, the temperature actually fell despite the fact that CO2 levels were increasing monotonically year on year. Surely if CO2 levels determine the temperature, the latter should have risen between 1945 and 1977, rather than the converse.
Although some 80% of the total manmade CO2 has been emitted since 1945, more than half of the warming observed in the past century occurred between 1890 and 1945, which could not have been a result of CO2 emissions. Of course, we may have more warming to come from those later emissions of CO2. We don't know yet.
It may be concluded that CO2 does not cause planetary temperature rise, but there are other regulatory systems at work. Now, it is impossible to state that the present unprecedentedly high levels of CO2 will not cause the earth to warm to the extent that the climate models indicate, but there is no direct evidence that recent global warming is caused by rising CO2 levels.
It has been argued that if global warming is not caused by CO2, then mathematical predictions of global catastrophe are meaningless, and we enter the red-zone of an arrogant belief that we can re-engineer the earth systems by curbing our carbon emissions, and hey presto global warming will be switched-off. As noted, the inertia in the system may be far greater than these models indicate if the ocean sinks for CO2 are becoming saturated.
There are however two imperatives. Firstly, we have to use less oil, gas and ultimately coal because these are present only in finite reserves, and so energy efficiency and conservation in relocalised (less transport-intensive) societies appears a must. It becomes arguable just how much of our effort and resource should be spent on actual carbon-remediation schemes (e.g. biochar production and other carbon capture technologies) , if CO2 is not the problem, and the earth has its own agenda irrespective of what we do.
Moreover, if we cannot ameliorate global warming, surely it makes more sense to devise strategies for how to survive under the stresses that it will impose upon us, in terms of sea-level rise, keeping those in vulnerable health comfortable during especially hot periods, and providing enough water for all of us. We need to take realistic and practical action. The rest is theory, untested and probably untestable until nature's own plan is revealed to us in full.
"CO2 might not be cause of climate change." By Dr Don J. Easterbrook. htt://www.mtexpress.com/story_printer.php?ID=2005114101