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Few realistic scenarios left to limit global warming to 1.5°C

Of the over 400 climate scenarios assessed in the 1.5°C report by the Intergovernmental Panel on Climate Change (IPCC), only around 50 scenarios avoid significantly overshooting 1.5°C and only 20 of them make realistic assumptions on mitigation options, for instance, the rate and scale of carbon removal from the atmosphere or extent of tree planting. The study warns that the realistic window for meeting the 1.5°C target set out in the Paris Agreement is very rapidly closing.

Lila Warszawski from the Potsdam Institute for Climate Impact Research (PIK) said that none of the realistic scenarios relies on a single silver bullet.

“The energy sector is key to the 1.5°C target of course, with on the one hand reduction of energy demand and on the other decarbonisation of energy use and production,” said Mrs Warszawski. “Yet, we can’t do away with the other strategies.”

And we have quite a list. As Mrs Warszawski noted, removing CO2 from the atmosphere and storing it underground also proves to be almost indispensable. Land use must become a net carbon sink, for instance by re-wetting peatlands or afforestation. Finally, emissions of the powerful greenhouse gas methane must be cut from animal production, but also from leaks in oil and gas extraction.

“We need a sustainability revolution to rival the industrial revolution. Otherwise those most vulnerable to climate change are going to bear the brunt of missing the 1.5°C target,” said co-author Tim Lenton from Exeter University.

Nebojsa Nakicenovic from the International Institute for Applied Systems Analysis (IIASA) reminded that this is a complex process. The first is to half global emissions every decade and a decarbonisation revolution by phasing out fossil energy. This has to be complemented with energy efficiency and sufficiency, and climate-friendly behaviours and diets. We also have to pursue nature-friendly carbon removal through afforestation and land-use change and finally ensure the safe operating of Earth systems that now remove half of the global emissions from the atmosphere.

Those scenarios classified by the analysis as unrealistically optimistic most frequently tend to over-estimate carbon capture and storage potentials, while others over-estimate energy consumption or reduction of non-CO2 greenhouse gases like methane.

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 Shell. Both scenarios foresee net emissions falling to zero globally as late as 2070. The researchers found that they do not lie within the corridor of carbon dioxide emissions over the next century which seems to offer a realistic chance of meeting the 1.5°C target.

“The necessary emissions reductions are hard to achieve, technically but also politically as they require unprecedented innovation of lifestyles and international cooperation,” concluded co-author Johan Rockström from PIK. However, as he underlined as technical as this all might sound, it really is about assuring a safe climate future for all.

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