The world of climate science is awash with computer models that seek to predict – across a range of carbon emission scenarios - how much our world will warm, and how quickly. But there is another way to get an idea of what our world will look like in 2100 and beyond: looking back to past episodes in the history of our planet when carbon levels were comparable.
The idea that the past is the key to the present is a tenet worth much in the fields of Earth Science and geophysics, and it makes perfect sense. In the same way that observing natural processes happening today can help us interpret events within the geological record, so what happened thousands or millions of years can tell us what to expect on 21st century Earth.
The latest news from deep time is not good. In fact, it is terrifying. Around 252 million years ago, the geological period known as the Permian was brought to an abrupt end by the greatest mass extinction event in the history of our world. Known as the Great Dying, it saw almost all marine species wiped out, along with two thirds of all life on land. What caused this cataclysmic dieback has been a matter of debate and controversy in geological circles for many years. Now, though, it looks as if the culprit has been fingered – climate change.
The results of a new study published earlier this year1 by scientists from Stanford University and the University of Washington provide robust evidence for a huge spike in warming at this time, with global average temperatures climbing as much as 10°C in as little as a few hundred years. As a result, the warmer oceans may have lost up to four fifths of their oxygen, leading to the obliteration of 96 percent of all marine species. On land, the extreme temperatures wiped everything - from lizards and insects to early plants and bacteria - from the face of the planet. The cause of the temperature spike is not certain, but up there as the favourite is a massive outburst of greenhouse gases triggered by elevated levels of volcanic activity.
Substitute volcanic activity with the repeated annual injection into the atmosphere of more than 35 billion tonnes of carbon dioxide, and the situation begins to look horribly familiar. But surely, you might say, even the worst case scenarios don't predict a 10°C rise in global temperatures, do they? Well, on the basis of current trends, the best we can hope for is a global average temperature hike of 3°C by 2100; nearer 4 or 5°C – or even more – should feedback loops really start to kick in as expected. That is already half way to the Great Dying, and would see countless species wiped out in a continuation of the ongoing, human-induced, sixth great extinction.
Even worse, if we burn most (not even all!) known fossil fuel reserves, it has been calculated that our world could end up a staggering 16°C warmer than during pre-industrial times.2 At the moment, the average temperature of Planet Earth is a little over 14°C. Such an increase would take it to more than 30°C. The result would be a mass extinction to put the Great Dying in the shade, and one that the human race would struggle to survive. Under these furnace conditions, most of the planet would simply be too hot for human physiologies to function, so the best prognosis for our race would be the survival of a few pockets clinging on in the slightly cooler polar regions.
So, it is perfectly clear. We now know exactly what trajectory we will be on if we continue to burn fossil fuels and swamp the atmosphere with carbon. Not back to the future, but forward to the past. We can't let it happen.
Bill McGuire is Professor Emeritus of Geophysical & Climate Hazards at UCL and author of Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis and Volcanic Eruptions. He was a contributor to the IPCC 2012 report on Climate Change & Extreme Events and Disasters.