Most people will agree that it is useful to look at the past to predict the future. This is explicitly the basis for all predictive models on climate change. One thing that some of these models do is predict extinctions of plants and animals based on changes in temperature. (Of course temperature is only one dimension of any organisms ecological niche, but it is relatively easy to model and we know a lot about temperature). But just as we can use this methodology to look into the future, we can also look back at known extinctions in the past and ask how they may have been influenced by changes in the environment.
We know that in the not so distant past many large animals have gone extinct or suffered enormous shrinkage of their ranges. The Woolly Mammoth would have been a common sight just 21 thousand years ago, but it was completely extinct only six thousand years ago. What drove these majestic animals, which were about the size of African Elephants, their close relatives, over the edge? And what about the other extinct mega-fauna? Woolly Rhinos, the European Cave Bear, and many more species disappeared from our planet just as modern humans ascended. Was it climate change or human impact that drove them to extinction?
According to this 2011 paper by Lorenz and his large team it was probably both. It seems that the Woolley Mammoth experienced a shrinking range and its populations broke up into smaller populations that suffered from inbreeding. Some species, which are not extinct like the Musk ox or the Reindeer, also experienced shrinking ranges, but escaped the genetic inbreeding. The authors know this from looking at thousands of specimens and close to a thousand ancient DNA sequences.
Around the same time humans flourished and hunted the Mammoth. If you come to Norman, OK and visit the Sam Noble Museum of Natural History you can see a life-sized bronze of a Mammoth under attack by two humans and a dog. Or maybe it is the other way around–the humans look so small and vulnerable against the enormous pachyderm. Nonetheless, this hunting may have had a significant impact on the populations of these long-lived, slowly reproducing animals. Up to 40% of European and Siberian Paleolithic sites have been found to include remains of Mammoths, indicating that there was hunting pressure on this species.
But in the end the data on this species are inconclusive and it seems that clearly a combination of changes in the climate and human impact interacted to drive this species to extinction. In other species, different patterns are found. For example, it seems that Musk oxen are extremely intolerant to changes in temperature and were driven north as temperatures rose.
And this is the main point of the Lorenzen paper: responses to the unique combination of climate change and human impact are highly idiosyncratic, and not easy to predict. Without very detailed knowledge of the biology of individual species, precise models of climate change, and a much better understanding of species interactions, we will experience many surprises, good and bad. Anthropogenic climate change is certainly a major factor in the “sixth great extinction” that is associated with the Anthropocene. But as the full range of Anthropocene research shows, humans influence their environment in many other ways too. We create countless interactions, all of which may contribute to extinctions.
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There is a recent additional article on this from Science: http://science.sciencemag.org/content/349/6248/602.short