‘Possible Futures’. That is how Detlef van Vuuren calls the results of the model studies with which he researches climate policy and sketches scenarios for reducing greenhouse gas emissions. Van Vuuren is regarded as one of the leading climate scientists based on so-called integrated assessment models (IAMs) shows how the goals of the Paris Climate Agreement can be achieved. He was one of two lead authors from the Netherlands who contributed to the report of the IPCC, the scientific climate panel of the United Nations, which will be published this Monday afternoon.
According to Van Vuuren, the models he uses are “helpful to prevent you from just sketching something, to prevent it from becoming science fiction,” he says in a video call. “In doing so, you place the outcome of these types of model calculations in a debate about possible and desired futures. The models add knowledge about cohesion and technical possibilities.”
But there is also criticism of these integrated climate models. They would take insufficient account of human behavior and political decision-making. They would be too optimistic about technological solutions. And they cannot possibly take all kinds of unpredictable developments into account. Take, for example, the two biggest social events of recent years, the corona crisis and the war in Ukraine. They can have a major impact on emissions, but you cannot see them coming, so they are not included in Van Vuuren’s models.
Climate science was too slow for me
Wolfgang Knorr researcher
Stories
“Computer models really just tell stories,” says German climate scientist Wolfgang Knorr. That sounds somewhat derogatory, and it is intended that way. “They are seen as mathematical models and thus get a scientific touch, because data is put into them and because they contain equations about supply and demand, about price elasticity. But all sorts of arbitrary assumptions are made and fundamental choices are made for the processing of that data. For example, a fair distribution of emission rights and raw materials is never an option and energy consumption is exclusively demand-driven and not based on democratic decisions. People can use as much energy as they can afford. The models resemble a game of Monopoly, which you can never win on the basis of the principle of fair distribution.”
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Knorr wrote on the science website two years ago, along with his colleagues James Dyke and Robert Watson The Conversation a critical article about these kinds of computer models – the story quickly reached 500,000 readers on Earthday via Apple News. According to the authors, models create a world that seems logical and attractive because it gives the impression that all goals are still achievable. As a result, the models offer a false sense of control.
Ajay Gambhir is a researcher at Imperial College London’s Grantham Institute for Climate and Environment. Although he also works with IAMs himself, he still thinks that their importance is overestimated. “They are treated as robust scientific evidence, but they are abstractions of reality,” Gambhir said in a video call. “They rely too much on the neoliberal model of growth, growth, growth. But the outcomes do not necessarily refer to the real world. Its developers are too much in model country.”
Gambhir cites the carbon budget as an example, which is the amount of CO2 that humanity can still emit before the one and a half degrees of warming is exceeded. “There is a budget of about 400 gigatons to stay below 1.5 degrees Celsius. And we now emit about 40 gigatons per year. Then you know that you have to go down very quickly. You don’t need any complicated models for that. The complexity of the real world cannot be captured by the models.”
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Do the whole puzzle
Van Vuuren knows the criticism. He also knows that models have their limitations, but for him that does not detract from the value. “The great thing about models is that they force you to put the whole emission reduction puzzle together,” he says. “I can say that I can solve the climate problem with only wind turbines. But if I have to work that out in a model, I am forced to think about the whole thing. Is electricity alone sufficient or are other forms of energy generation also necessary? Can I design an electricity system based on wind energy that is sufficiently stable? How much land do I need? The strength of the model is that you eventually have to write out the whole story. And so we do that for different futures, including change of lifestyle and restriction of physical growth.”
That becomes more difficult, admits Van Vuuren, as soon as you start thinking about the distant future. “Ultimately, a lot is conceivable in 2100.” Furthermore, according to him, the climate models also have difficulty with “radically different futures”. Take a current flow as ‘degrowth‘, a concept that assumes a reduction in consumption and therefore economic contraction. For such a scenario, the past has little to hold on to, says Van Vuuren. “And that is at the expense of the power of the model, because it is difficult to sketch in detail what such a future looks like. But that doesn’t just apply to computer models. Everyone who advocates for degrowth faces the same problem. It has never been tried, so you know less about what such a future looks like.”
Wolfgang Knorr mainly focuses his criticism on the capture and storage of carbon dioxide. This happens in many model scenarios in such large quantities that it is completely unrealistic, according to Knorr. “In some IAM scenarios, 665 gigatons of CO2 be removed from the atmosphere. About half should be stored in suitable geological formations and depleted gas fields, the rest being taken up by newly planted forests. Do you know how much CO2 was buried underground between 1996 and 2020? 0.2 gigatons. And to get enough CO2 to capture in trees, you need 25 to 80 percent of the current cropland, which is 1.2 to 3.7 times the size of the whole of India.”
They are fantasy stories, says Knorr, full of “crazy, futuristic assumptions.” And as long as the climate models continue to suggest that the goals are still achievable, they will have a delaying effect on climate policy, according to Knorr. It will lead politicians to sit back and think that things are not going that fast.
An inspiration for ‘Paris’
Van Vuuren strongly disagrees with that. “Model studies explore a large number of futures – and we need to get to work quickly in all of them. In the formulations of the Paris Agreement you will recognize many texts that are inspired by the results of model studies. That is the only reason why policymakers have dared to make such far-reaching formulations, for example about the long-term target of one and a half degrees, but also about the goal of net-zero emissions by the middle of the century. This could be formulated thanks to the model scenarios that said it was technologically and economically feasible. Paris has been an inspiration for governments and companies. The fact that we have so much climate news is thanks to the Paris Agreement. The models have definitely contributed in a positive way to where we are now.”
Van Vuuren has noticed that policymakers like to hide behind the results of his models. “Reducing greenhouse gases is a very difficult task. You have to explain to society that we have to do many things differently than before, with considerable costs – certainly in the short term. It is then nice for a policymaker to say: I didn’t come up with this myself, I have to. It is attractive to absolutize the advice of scientists.”
But in the end, says Van Vuuren, these are political choices. That is where the mandate for climate policy lies. “That is why I try to outline the pros and cons of choices as neutrally as possible. I think that is precisely why I can convince more people that this is the right way. It is also a role that suits me. But I do see that more and more scientists are starting to feel uncomfortable, because they think that climate policy is moving too slowly. They are more activist.”
Wolfgang Knorr is such a person. When he wrote the article for The Conversation two years ago, he was still working as a physical geography and ecosystem researcher at Lund University. Now he lives in Greece, where he runs an olive grove with his wife. He calls himself a climate activist. “Climate science was too slow for me. At that rate, warming will not be stopped in time.”
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A version of this article also appeared in the March 20, 2023 newspaper