by Matt Dyson
Is global warming a natural phenomenon, or is caused by human activity alone? Thanks for the question Matt.
Answer from Climate-change-wisdom
Many lines of evidence tell us that over geological time climate changes in both directions as there have been periods of relative cold and periods of warmth.
Consequently global warming is natural.
The warming phases that happen to end ice ages have all been natural and there have been warming periods that have lasted or millions of years.
Back in the Permian, some 280 million years ago, there was a significant warming that took temperatures from something similar to those we have today to a considerably warmer climate over a short time geologically, perhaps a few hundred thousand years.
Another warming that lasted for a longer time, perhaps several million years, occurred in the Cretaceous about 100 mya.
So they happen and there have been very many of them long before humans were invented, and way before humans became numerous and figured out how to clear land and burn fossil fuels.
That said, what evidence we have does point to human activity being a trigger for the latest warming event. And the evidence is also strong that it is getting warmer.
Climate skeptics would argue that even if all this is true it makes no difference because warming has happened before.
Only in the past there have not been 6.7 billion people needing to be fed from a landscape that they have radically altered and an ocean they have plundered and polluted.
So its not that it happens, it’s that it happens to us.