As much as I doubt any rise in CO2 will have any catastrophic climate consequences, I had for some time understood that it was well established that the recent rise in atmospheric CO2 was pretty clearly attributable to humans. Maybe that's not the case... I haven't listened to the podcast referenced in the link yet, but apparently even Judith Curry is impressed. It will be interesting to see how the paper holds up once published. Andrew Bolt says in his Herald Sun blog: Salbyâ€™s argument is that the usual evidence given for the rise in CO2 being man-made is mistaken. Itâ€™s usually taken to be the fact that as carbon dioxide concentrations in the atmosphere increase, the 1 per cent of CO2 thatâ€™s the heavier carbon isotope ratio c13 declines in proportion. Plants, which produced our coal and oil, prefer the lighter c12 isotope. Hence, it must be our gasses that caused this relative decline. But that conclusion holds true only if there are no other sources of c12 increases which are not human caused. Salby says there are â€“ the huge increases in carbon dioxide concentrations caused by such things as spells of warming and El Ninos, which cause concentration levels to increase independently of human emissions. He suggests that its warmth which tends to produce more CO2, rather than vice versa â€“ which, incidentally is the story of the past recoveries from ice ages. Dr. Judith Curry has some strong words of support, and of caution: "I just finished listening to Murry Salbyâ€™s podcast on Climate Change and Carbon. Wow."