Challenges to the Climate Change Hypothesis

Why didn't climate change at other times of glacial retreat cause extinction?

If there had been only one huge advance and retreat of glaciation in the last 1.6 million years, most observers would probably conclude that what caused the end-Pleistocene extinctions was obvious and non-controversial. We know, however, that there were not one but many such advance-retreat episodes during the Pleistocene--at least two dozen moderate to large-scale episodes during the last 100,000 years alone. Yet massive extinctions only took place during the last retreat. Conclusion: A major problem with the notion that stresses induced by climate change at the end of the last ice age caused widespread extinction is that similar-scale extinctions ought to have been correlated with other ice ages earlier in the Pleistocene.

Why were warming conditions stressful for so many Pleistocene herbivores and plants?

We tend to think that the current association of species in communities is "normal." Thus we expect to find aspen and birch associated with conifers in northern North America, but not oak. However, 20,000 years ago, these species were not associated in the same manner. This suggests that communities are not rigid entities, but are instead composed of elements (species) that react individualistically to limiting factors such as temperature, precipitation, and so forth. Thus there is no basis for automatically assuming that climate change will lead to extinction. Changes that might work out to be a bad turn of events for one species may in fact represent an opportunity for others. While certain large herbivores may have reacted negatively to warming conditions, for others, both plants and animals, these changes should have represented an opportunity.