Professor of Biosphere and Climate Impacts Iain Colin Prentice on global warming, the science of ecology, and climate models with a long time perspective
I study the biosphere as a whole, and this is a relatively new development. Most of my work concerns the land’s biosphere, but, of course, the ocean has a biosphere in it too. The study of the biosphere on a global scale is something that’s relatively recent. The new perspective that we have now only dates back to about the 1980’s or so, when it had finally become clear that human activities were massively modifying ecosystems, and not just ecosystems but indeed the composition of the atmosphere. And that two things were interrelated.
But a lot of other changes in our way of looking at the biosphere came with this, because, of course, CO2 is fundamental to plant life, plants dependent on CO2, they take it up and decomposing microbes and put it back. And the flux involved is enormous, so large, in fact, that any perturbation to that flow of carbon dioxide into ecosystems and back out again, any small perturbation would be of a similar magnitude to the amount that we are releasing with fossil fuel burning. It’s gradually become clear that there is an intense interaction between the biosphere and the atmosphere, and that there is something which we now call the global carbon cycle which is the exchange of CO2 between the atmosphere and the ocean, and between the atmosphere and the land. That’s basically all one system.
With this new understanding of the biosphere there is a considerable pressure to develop global models of how ecosystems work, and how climate modifies ecosystems, how climate controls ecosystems, and how ecosystems then, in turn, influence the carbon cycle. It was also gradually becoming clear that ecosystems would have more direct effects on climate, because most of the water that comes into the atmosphere of land surfaces is actually coming through plants. Any change in the nature of the vegetation cover can influence the water exchange and it can also influence all the physical properties like the heat absorption.
We have system models, which are climate models, which are originally derived from weather forecasting models, but adapted to a longer time perspective, but these models now actually incorporate models of the biosphere. That seems like quite an achievement. But there are a few problems. One of the problems is that when they’re asked to make projections into the future on the various scenarios, they all give different answers. And I guess they can’t all be right. There are also have quite large biases. So there’s a lot of work that needs to be done. The models are getting more and more complex at the moment, but they’re not really actually getting better.
What has now been realized by many scientists in the field is that we need to do it better. With hindsight, in a way, we did this in too much of a hurry. Models have been developed independently by different groups without much cross-checking, without enough comparisons with data. Data here are a key issue, because when we first started to work on these models there were very few data of the large-scale kind that we would need to test all of our assumptions.