Mammals could go extinct in 250 million years time

The heat is on for mammals
29 September 2023

Interview with 

Alexander Farnsworth, University of Bristol


A heat map of the supercontinent


Scientists at the University of Bristol have said that heat is likely to eliminate nearly all mammals in around 250 million years time. By modelling the development of the Earth’s atmosphere, the movement of tectonic plates, and the activity of the Sun, it has been predicted that our continents will converge to form one huge land mass - which has been dubbed Pangaea Ultima. It’s predicted that temperatures on this supercontinent could exceed 50 degrees Celsius. So, what should we expect? The study’s lead author is Dr Alexander Farnsworth.

Alexander - There are three really main processes here that we want to kind of really try and understand what's going on. First you have all these big continents now merging together into this one big supercontinent. And the first thing to really take into account here, and it's really important, is this big supercontinent is essentially centred on the equator. So most of the land mass is already in the hot tropics. On top of this, you then get this big seasonality effect that you get with these sorts of big supercontinents because you have these big interior regions but become very, very hot and dry. And this happens because the further away you go from the oceans, the less you get the influence of those oceans and oceans tend to, for in the case of the UK, it actually keeps us warmer in the winters because it's transported a lot of heat northward and that heat tends to stay in the oceans a lot longer than, say, on the land surface which dissipates that heat quite quickly. So the further away you go from these oceans, the less of an influence it can have. Kind of akin to almost what you might see in the middle of Canada and America or middle of Russia where you can have very, very hot, hot summers. The next factor we kind of really need to take into account is what is the sun doing? And we can kind of predict exactly the trajectory of how much brighter the sun will be in about 250 million years. So it's in the general region about 2.5% brighter. So two and a half percent more energy is gonna be emitted by the sun. Then we have this sort of third factor going on and it's what CO2 is doing. When these sort of plate tectonics start to converge and they start to kind of hit and bang into each other and plates subduct under one another, it has an impact on the mantle. This creates a lot of volcanism and that volcanism, as we know, can spew up a lot of CO2 over a long time period into the atmosphere. And what we're predicting is we're looking at, you know, CO2 values that might be up to double what we see today.

Will - Really is a horrifying sounding future. That being said, there are places on Earth currently that hit 50 degrees centigrade not infrequently. They are not ecological paradises. So in the future, which animal groups are going to be hit the hardest by this?

Alexander - We know from our study that we think mammals are certainly going to be hit quite hard. Now a question you might want to ask is, okay, we know in the past it was much, much warmer, much, much hotter than it is today. So why didn't mammals go extinct then? And this is generally again down to where the supercontinent is situated in these very warm tropics. Now most mammals in the past, they've been able to escape a lot of these hot temperatures by moving towards the poles into these other regions, which would be much cooler, which you couldn't do in the future because you don't have these polar regions with land surface anymore. So that's already taken away, that sort of refugia from the heat. So then they have to try and figure out other ways to adapt to this heat. So then you might want to ask yourself, okay, what about evolution? 250 million years is a long, long time in the future. The problem is with our mammal physiology, we tend to have an upper limit. We really only think you can increase that upper level threshold by about 0.6 Celsius per million years. So that's very, very slow. So at these sort of timeframes we're talking about, we're just not going to be able to evolve fast enough. And this is mainly because, when you get this supercontinent formation, you then start to get this rapid rise in temperatures, which is just going to be too fast-paced for evolution to really ameliorate that impact.

Will - Well now that everyone is suitably depressed, I wanted to ask you about planets that aren't Earth. Because this study strikes me as something that could be very useful in aiding our search for other habitable planets, should we want to leave this one in the future for whatever reason. Because I suppose I've always naively thought of every planet we look at just staying how it is forever. But what if we end up journeying out to another planet only to find that in the time it took there, these planet's plates have shifted and it's no longer habitable?

Alexander - For us, this was quite an interesting side point that came out of this research. So you can imagine if you are NASA, you only have the budget for one space mission to a planetoid. And we maybe have a space telescope, which is powerful enough to see two different planets, both in a habitable zone, one planet with a big supercontinent in the centre and the equator versus one planet with sort of these fragmented continents like we have today. And you need to target which planet you really want to go to. For me, I would definitely push towards going to these fragmented continent planetoids to have a look and that would be a much better target for potential habitation.

Will - And just as a final question, is this the end of mammals as we know it in your opinion?

Alexander - <laugh> See, it's a great question. Undoubtedly there are still some parts, when we predicted the worst case scenario, about 8% of the land surface might only be habitable for mammals in these. So there is a little bit of land in especially the north part of this continent, which mammals could live in. Now you can make the assumption there's still lots of extreme weather going on here. There's still lots of other problems that are going to have big, big changes going on, lots of competition from other species. So will these mammals outcompete all these other species? It remains to be seen. Do they continue to dominate afterwards? Potentially, you never know. They are very adaptable species of mammals. We have shown this great resilience to looking at different extremes in temperatures. Or if the temperature is still going to stay significantly hot for tens or hundreds of millions years thereafter, maybe reptiles might become more preferable or even the birds might be more preferable because they have a higher heat resilience than mammals most mammals will have. And they are able to migrate over vast distances too, so they can change where they live a lot more readily than most mammals can. So, in a funny roundabout way, these dinosaur birds might end up becoming the new dinosaurs and dinosaurs will reradiate back over and take back over the Earth.


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