Recently, I stumbled across this graph from the Smithsonian Institution, showing us the estimated global temperatures over the last 500 million years. I added some colour to highlight the difference between a world with ice caps, as we know it, and a warmer world without ice:
The sharp uptick at the right end is our doing by burning all the coal and oil, which took millions of years to form. You can see that all of human history, plus our evolution was spent in the cold, blue region. But for more than half of the 500 million years the earth’s climate was a lot warmer. So, what is the problem if we are heading back into an ice-free world?
The problem is the speed at which we are warming our world. This is unprecedented. Temperatures also rose at the end of the Permian period, 300 to 260 million years ago, probably due to extensive and widespread volcanism and subsequent rising CO2 levels, but that happened over hundreds of thousands of years. We are now doing the job over a few centuries, and who knows how quickly the warming will stop once we reached a peak in CO2 concentrations.
Looking at the diagram you might ask where are the recent ice ages? If you print the above graph in landscape on an A4 sheet of paper, one million years would be 1/2 millimeter (or 1/64th of an inch, for our British and American friends). In other words, all the ice ages are squeezed into one tiny dot.
Let’s use a logarithmic timescale to see what is going on in more recent history:
Graph by Glen Fergus
Up to around 800,000 years ago we get reliable data from ice core samples (O16/O18 and H/D ratios), and there is good agreement from samples taken in Antarctica and Greenland. Data from further back in time are derived from seafloor deposits and geological features.
The next graph shows the last 800,000 years in more detail:
Are we heading into uncharted waters? Well, the earth will survive, it has been through this before. People will adjust and survive. Unfortunately, man-induced climate change will trigger a mass extinction of plant and animal life. Will it cause a runaway hothouse planet that will see our planet ending up like our sister planet Venus? This seems highly unlikely.