The most common position among climate change alamrists is that we need to stabilize the atmospheric concentration of carbon dioxide somewhere between 450 and 550 parts per million (ppm). That is, for instance, the target range endorsed by Nicholas Stern. It is also thought by many to be compatible with the EU goal of generating less than two degrees Celsius of temperature increase by 2100, though that is only really plausible at the low end of this range.
In recent Congressional testimony, James Hansen, director of the NASA Goddard Institute for Space Studies, argued that we actually need to cut concentrations from the present 385ppm to 350ppm or less. Basically, his argument is that even stabilization at the present level would have unacceptable consequences: both directly, in terms of impacts on physical and biological systems, and by kicking off feedback loops that will further worsen things. The distinction between the numbers may seem abstract to those not familiar with climate policy, but the practical differences between stabilizing between 550, 450, or 350ppm are massive.
Where do these numbers come from? They come from flawed and partial computer models which assume that any rise in the volume of CO2 leads to a rise in temperature. This is the basis of the view that we have less than 100 months left to “save the planet”.
So some history. CO2 levels are currently low, relative to other periods of climate history. Atmospheric CO2 levels were more than 4,000ppm higher than those of today (yes, that’s a full order of magnitude higher)in past climate history. Granted, continental configuration now is nothing like it was then, Sol’s irradiance differs, as do orbits, obliquity, etc. There is no obvious correlation between atmospheric CO2 and planetary temperature over the last 600 million years. Further, temperature levels are a precursor to levels of CO2 (the temperature of the oceans affects absorption levels) and the extent to which CO2 is absorbed is a function of complex processes, not the simple dynamics of the models used to create the scare scenarios.
So why would such relatively small amounts of CO2 suddenly become a critical factor now? Do you think it may have something to do with a new President, a meeting of the G20 in April and the political moment – an attempt to use climate “catastrophe” (it is no longer global warming) as a basis for rolling back development?