Modeling the future
There are a lot of things that determine whether humanity can meet the targets set out in the Paris Agreement. Reducing carbon emissions will require significant action in the agriculture, transportation, and energy sectors, to name just a few of the key players. The economy, land use, population growth, climate mitigation strategies, and, of course, human behavior, all play important roles as well.
The models used to inform climate policies—called integrated assessment models—incorporate various combinations of all of these factors, as well as calculations of how they impact each other. These models are designed to answer “what if?” type questions to inform our policy options. In the case of this current research, the key questions were: “how will carbon emissions, temperatures, and the global GDP compare in the two scenarios” (i.e. if temperatures overshoot the Paris targets, even temporarily, or not); and “how will each of these likely turn out under the world’s combined emission reduction pledges (nationally determined contributions) as of 2020?”
Different research groups around the world have developed dozens of models, each of which more or less focuses on certain interactions. For example, one model, MESSAGE, is designed to explore how energy systems can meet demand at minimal costs. Another, REMIND-MAgPIE, focuses more on agricultural production and land use. Other models place more emphasis on environmental effects or technology costs; some even use game theory to predict the impacts of whether climate action is cooperative or not.
By comparing the outputs of nine of these different models, the result of this latest study is the most comprehensive and systematic effort to explore the economic attainability and consequences of current and potential strategies for meeting the Paris targets so far.
Longterm payoffs
Not surprisingly, minimizing temperature overshoot will require much greater investments in the short term (starting within the next 10 years). But all of the models project that these upfront costs will result in a higher global GDP (up to 2 percent higher) by 2100, with most showing benefits already by around 2080. The authors note that greater investments in the short term will likely be fully compensated by more GDP growth in the second half of the century.
“The key is to reach net-zero emissions around mid-century, and our study shows that this requires both a very strong reduction of the use of fossil fuels and additionally at least some scaling up of options for removing carbon from the atmosphere,” wrote Bertram. “In the first article based on this study (published in summer), we showed that in the short-term, the critical factor is the decarbonization of the power sector, mostly via rapid expansion of renewable energy.”
In order to avoid overshoot, the models estimate that the world needs to reach net-zero emissions by 2045-2065. Allowing overshoot (but achieving targets by 2100) would push our net-zero deadline out to 2060-2070, but this would mean an extra 0.08-0.16° C of warming and the potentially irreversible damage that could accompany that.
Short-sighted pledges
Meeting the Paris targets via a path that allows overshoot also has long-term benefits for GDP, but they’re not as high as when temperatures never exceed the goals. Unfortunately, the authors show that the world’s emission pledges as of 2020 are far from achieving either scenario. Under these pledges, carbon emissions will still be two- to several-fold higher than needed. Although these scenarios correlate with a better global GDP for roughly the next 20 years, things go bad afterward, with the GDP reduced by up to 3 percent for the ensuing 60 years (with no predictions for what happens after that).
“I would say that [political discussions] partially already have pivoted to a focus on limiting peak temperature gradually. With the Indian announcement at Glasgow, now the 7 biggest emitters have targets for net-zero emissions in mid-century or thereafter—which already, if fully implemented and achieved, would go a long way for limiting temperature increase,” wrote Bertram. “The crucial issue now is that current 2030 targets are not in line with achieving these net-zero targets in a balanced way with immediate decarbonization, and would thus lead to higher peak temperatures than if efforts would be started right away.”
Without significantly more action and investments than current policies are allotting, the authors’ models project that it won’t be feasible to meet the Paris Agreement. A clear caveat of these findings is that these are models and none of them can capture all of the variables involved. But it does say something that they all agree on the general trajectory on which we’re headed.
