Last year I mentioned I would focus my teaching in our Climate and Climate Change module on periods climate models have picked as potential analogies for our near future. As I write this, atmospheric CO2 is at approximately 420 ppm. In a normal interglacial period, it is 280 ppm. You have to go millions of years back to reach a value as high as 420. And you have to go even further back to find the values that are expected for the year 2100. If you want to chase the values we might reach if we end up in a high emissions scenario, you have to go tens of millions of years back.
I mentioned all this before. This year I'm teaching that again. But if I teach something for the first time, I am never satisfied with it! So this year I am spending quite a lot of time reading up more on these time periods, and what the modelling attempts tell us. What are the things the models are struggling to reconstruct? What are the things the models can't agree on? These are probably the aspects of our climate system we struggle to catch in equations, or of which we don't have sufficient understanding yet.
There are still some serious issues with faithfully reproducing these times. Ocean circulation still seems to be difficult to get right. Just how much warming you get from a certain increase in greenhouse gases as well. And the temperature contrast between the equator and the poles also seems to be difficult. So these would be among the things that can still throw us a curveball.
It is a fair bit of work, but it is fascinating stuff! And my guess is that next year I will do it again to make the series even better…
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