text: Naturally they claim this ancient forest was wiped out by global warming, somehow forgetting to mention that for hundreds of millions of years prior to the Carboniferous age atmospheric carbon dioxide had been somewhere north of 3,000ppm, possibly far north. The later Permian warming occurred when CO 2 was at about its lowest point in at least 300 million years the only other time it is thought to have been as dangerously low as todays meager levels.