INTERVIEW [5min read]

Keeping it real: reliable, robust predictions for the future of ecosystems

Prof. Iain Colin Prentice

Earth system models have contributed invaluably to our evolving understanding and awareness of climate change. Yet, fundamental limitations to these mathematical tools remain, not the least of which is their tendency to deliver contradictory results. Pointing the finger at their unnecessary complexity, Prof. Iain Colin Prentice and a number of other world-renowned scientists have undertaken the mission to produce a new generation of models of the global land surface, resting on secure theoretical and empirical foundations. The overall objective is to develop robust, quantitative knowledge about the impacts of environmental variability and change on land ecosystems, as well as their interactions with the atmosphere. Prof. Iain Colin Prentice looks back on the achievements of the Chair, on the role of AXA and on the impacts his results have had already.

How can the progress made during your time in the Chair contribute to the improvement of Earth System models? And what are the new developments exactly?

If we are to understand and predict what will happen to our planet in the future, being able to measure and predict carbon uptake by plants is an absolute prerequisite. However, we lack firm knowledge on this topic. For that reason, our main achievement, I would say, is the development of a satellite-based model that does a good job of predicting the total uptake of carbon in photosynthesis (aka "gross primary production" or GPP) across the ecosystems of the world. The model is remarkably simple, yet it performs much better than many models that are far more complicated. Basically, it just analyzes data and necessitates minimum added parameters. Part of the model development was theory – I showed that the "light use efficiency" formulation (which means GPP is proportional to the amount of light absorbed by leaves) has a sound basis when allowance is made for the way properties of the leaves change over time. I have shown how the temperature of leaves (provided the plants have sufficient water supply) is buffered, so leaves in cold climates tend to be warmer than the air while those in hot climates tend to be cooler than the air. I have shown how this can be predicted, and that it is true based on an analysis of satellite observations of the temperature of the land surface. This is crucial information in regard to climate change and predicting how vegetation will respond to the shifts in temperatures. What is more, I have developed a model that correctly predicts how the thickness of leaves (leaf mass per area, LMA) relates to their lifespan, and how this relationship shifts according to light intensity, the length of the favorable growth season, and other aspects of climate. These mechanisms are all cogs in the ecosystems machine, and what we are doing is reassessing them, finding simple ways to explain and predict them, to make sure that our vegetations models are based on sound information. I have also shown how the new GPP model can be adapted with minor additions to predict the grain harvest in wheat crops, how they vary from year to year and how they may change under different scenarios of changing CO2 and climate.

Have you discovered anything you were not expecting?

In 2017, I published a paper on the predictability of nitrogen in the leaves of wild plants. One implication is that leaf nitrogen does not determine photosynthetic capacity, as many models assume, but rather, photosynthesis is optimized at the leaf level, and the metabolic component of leaf nitrogen simply follows from it. In other words, plants are smart! This is a very controversial paper, because it goes against a commonly assumed principle. In total, I have published almost 100 peer-reviewed journal articles since the start of my AXA Chair.

Is your research going to change the way in which plant ecology and land ecosystem modelling are currently approached?

As far as the research community is concerned, another crucial output of the research I’ve conducted with the help of my AXA Chair is the setting up of an international consortium to pursue the development of “next-gen” vegetation models, based, in part, on the work I’ve just mentioned. The consortium includes members from UC Berkeley, Texas Tech, Reading University, ETH Zurich and Tsinghua University. It has also extended to include participants from the Universities of Pittsburgh and Utrecht. We meet monthly by Skype and also communicate via a Slack group. Slowly but surely, my research is changing plant functional ecology and land ecosystem modelling. Ideas once considered "left-field" are becoming accepted, and new directions in land-surface modelling for weather, climate and Earth System applications are being pursued based on my recent research.

How is your research likely to impact our lives in the future?

It will come more slowly, through the general adoption of more reliable models for the impacts of climate change on ecosystems and how ecosystem processes influence the carbon cycle and climate. With better models will come a new-found ability of science to deliver actionable information on climate-change adaptation in the context of the Sustainable Development Goals. I’m hoping that the whole issue of climate change and impact on biosphere will become clearer. When you have a lack of firm knowledge, or agreed knowledge I should say, there is space for all kinds of opinions. It creates room for politicizing, which is very unhelpful when it comes to moving things along. We need another paradigm shift in Earth system modelling. There was time when we thought global Earth system models weren’t even possible. Now, we need to prove that reaching firmer accuracies is within our grasp, that we can develop models that don’t contradict each other. We couldn’t before, mainly because of the scarcity of data, but this is no longer the case. Data is the key issue here. Now that we have access to precise measurements on a lot of parameters, the situation has changed radically. We can use this data to validate our models. This is what I’m doing along with the next-gen vegetation models consortium, and I have no doubt that these ideas will be accepted. It’s all about the consolidation of knowledge.

What role has AXA played in the success of the project and in your career?

The AXA Chair has allowed me the freedom to pursue research leading to important recognition both for me personally and for Imperial College. Since the start of my AXA Chair, I have received funding from the European Space Agency for the TerrA-P project, a global monitoring system based on satellite data, and a European Research Council (ERC) Advanced Grant for the REALM project (Re-inventing Ecosystem And Land-surface Models). What is more, I have been elected as a Fellow of the Royal Society and taken up a new leadership role as Director of the Leverhulme Centre for Wildfires, Environment and Society. I have also been appointed as a High-End Foreign Expert at Tsinghua University.

What are your next major projects?

I am on course to create, in collaboration with colleagues in the next-gen vegetation model development group: a comprehensive "optimal trait theory" linking all the most important properties of plants in a common theoretical framework. We also aim to improve our understanding of the global-scale coupling between the carbon and water cycles, which is largely regulated by plants; as well as our understanding of the past, present and future of the global carbon cycle and fossil-fuel CO2­ uptake by ecosystems on land.

Who is Colin Prentice?

Professor Iain Colin Prentice is a world-renowned expert in climate sciences, ecology and environmental biology. From 2012 to 2019, he held the AXA Chair in Biosphere and Climate Impacts at the department of Life sciences, Imperial College, London. He is currently the director of the Leverhulme Center for Wildfires, Environment and Society and holds an honorary professorship in Ecology and Evolution at the Macquarie University in Sydney. He has a PhD in botany (pollen ecology) from the University of Cambridge.

April 2020 | Photo: @viniciusbenedit

Know more about Prof. Prentice's project

Chair in Biosphere and Climate Impacts