Guest essay by Eric Worrall
Academics Emma Dunne and Bethany Allen think we are heading into a new climate driven mass extinction – but they admit Earth still has polar icecaps, and global species diversity shows an “ice house” pattern of peaking in warm tropical latitudes.
Prehistoric creatures flocked to different latitudes to survive climate change – the same is taking place today
June 28, 2021 7.37pm AEST
Life on Earth is most diverse at the equator. This pattern, where species biodiversity increases as we move through the tropics towards the equator, is seen on land and in the oceans, and has been documented across a broad range of animal and plant groups, from mammals and birds, to ants and even trees.
Despite this pattern being so striking today, the distribution of biodiversity across latitudes – called the latitudinal biodiversity gradient – hasn’t always been like this. Studies looking at the evolution of biodiversity by latitude have shown that during some intervals in Earth’s history, species biodiversity was actually highest at latitudes far from the equator.
Modern biodiversity peaks in low-latitude equatorial regions, such as in the tropical rainforests of the Amazon and central Africa. This pattern is more likely to be recorded during “icehouse” times, when ice sheets are present in both poles simultaneously – like today.
During warmer intervals, called “hothouse” or “greenhouse” Earth states, bimodal peaks have been recorded. This means there were two bands where biodiversity was highest, and these wrapped around the Earth at mid-latitudes, or regions sitting between 25° and 65° north and south of the equator.
The part Bethany and Emma left out was that for most of the Earth’s history, including previous cool periods like the Carboniferous (800ppm), CO2 levels were much higher than today (420ppm). The Cretaceous, the age of the dinosaurs, was only 4C warmer than today, but had a staggering 1700ppm CO2.
What I am saying is, even if CO2 is the main driver of climate change, to achieve anything like the species redistribution Bethany and Emma are talking about would require around seven hundred years of burning fossil fuel at our current rate. That is simply not going to happen – we shall run out of recoverable fossil fuel reserves, long before we have a geologically noticeable impact on the global climate.