Of the more than 400 climate scenarios assessed in the 1.5 ° C report from the Intergovernmental Panel on Climate Change (IPCC), only about fifty scenarios prevent a significant exceedance of 1.5 ° C. On of that number, only about 20 make realistic assumptions about mitigation options, such as the rate and extent of carbon removal from the atmosphere or the extent of tree planting, according to a new study . The 20 scenarios must pull at least one lever of mitigation to “difficult” rather than “reasonable” levels, according to the analysis. Therefore, the world faces a high risk of exceeding the 1.5 ° C limit. The realistic window to reach the 1.5 ° C target is closing very quickly.
If all the climate mitigation levers are pulled, it may still be possible to limit global warming to 1.5 ° C under the Paris Agreement. The findings could help inform the heated debate on climate policy. “The emission scenarios differ in their dependence on each of the five mitigation levers we examined. Yet all the scenarios that we consider realistic pull at least several levers to difficult levels, ”says lead author Lila Warszawski of the Potsdam Institute for Climate Impact Research (PIK). “None of the realistic scenarios relies on a single silver bullet.”
All realistic scenarios pull the five levers
“The energy sector is of course the key to the 1.5 ° C objective, with on the one hand the reduction of energy demand and on the other hand the decarbonisation of consumption and production. energy, ”says Warszawski. “Yet we cannot suppress the other strategies. Removing carbon dioxide from the atmosphere and, for example, storing it underground, is also almost essential. Land use must become a net carbon sink, for example by rewetting peatlands or reforestation. . Finally, emissions of the powerful greenhouse gas, methane, must be cut from animal production, but also from leaks in oil and gas extraction. It’s quite a list. “
The researchers drew on existing research to define the limits that define the “reasonable”, “difficult” and “speculative” use of each of the levers in the middle of the century. The limits quantify the range of emission reduction potentials of each of the aggregate levers, which result from technological, economic, social and resource considerations. They can then be translated into contributions to maintain warming at 1.5 ° C without temperature overshoot or at low temperature.
A triple challenge for humanity
“This requires an immediate acceleration of global action to reduce greenhouse gas emissions by all available means,” says co-author Tim Lenton of the University of Exeter. “We need a sustainability revolution to compete with the industrial revolution. Otherwise, those most vulnerable to climate change will be the hardest hit by missing the 1.5 ° C target. This is a challenge. system-wide – piecemeal actions and rhetorical commitments are not going to be enough. “
“Humanity faces a triple challenge to stabilize global warming without significantly exceeding the 1.5 ° C commitment,” says co-author Nebojsa Nakicenovic of the International Institute for Applied Systems Analysis, IIASA. “First, halving global emissions every decade, which requires a Herculean effort and a decarbonization revolution by phasing out fossil fuels, a leap forward in efficiency and sufficiency, and behaviors and regimes. climate-friendly food; second, to pursue nature-friendly carbon elimination through afforestation. and land use change; and third, to ensure the safe functioning of earth systems which now remove half of the world’s emissions from the atmosphere. “
Unrealistic optimistic scenarios overestimate, for example, the potential for carbon capture and storage
Scenarios classified by the analysis as unrealistic optimistic tend to overestimate the potential for carbon capture and storage, while others overestimate energy consumption or the reduction of non-carbon greenhouse gases. CO2 like methane. Still others make too bold assumptions about dietary changes to more plant foods or about limited population growth.
The authors also took a closer look at the scenarios provided by the International Energy Agency (IEA) in 2018 and the one called “ Sky ” produced by the oil and gas company Shell. Both scenarios predict that net emissions will drop to zero globally until 2070. The researchers found that they do not lie in the corridor for carbon dioxide emissions over the next century, which appears to be true. offer a realistic chance of reaching the 1.5 ° C target. The Shell Sky scenario shows emissions levels in 2030 that are much higher than the other scenarios considered in this study.
“The Shell Sky script has been called a pie in the sky, and indeed it is,” says co-author Gail Whiteman of the Business School at the University of Exeter. “From a scientific point of view, it’s pretty clear. In the business world, some still appreciate it because it seems to offer, compared to other scenarios, a relatively easy solution to get out of the climate crisis. Our analysis shows, however, that there are no easy solutions. “
Regardless of the specific climate target, rapid emission reductions are essential
“The necessary emission reductions are difficult to achieve, technically but also politically. They require unprecedented innovation in lifestyles and international cooperation,” concludes co-author Johan Rockström of PIK. “I understand anyone who thinks we might not meet the 1.5 ° C target. Moreover, it is clear that regardless of the specific climate target, it is now essential to quickly implement large reductions in water. emissions. Still, I think limiting the warming to 1.5 ° C is worth all the effort. because it would limit the risk of giving additional impetus to certain tilting elements of the Earth system, such as ice caps or ice caps. ecosystems like the Amazon rainforest. As technical as it sounds, it’s really about ensuring a secure climate future for all. “