Research press release


Nature Climate Change

Climate change: Immediate emissions cuts needed to avoid further warming



今回、Michele Dvorakたちは、温室効果ガス排出量に基づいた気候モデルを用いて、2021〜2080年の排出量抑制経路(IPCCのAR6報告書で使用されている共通社会経済経路(SSP))の現行の経路とそれ以外の経路の下での不可避的温暖化(過去に排出された温室効果ガスの波及効果)を調べた。Dvorakたちは、温室効果ガスの排出が直ちに停止されれば、1.5℃を超える地球温暖化が不可避となる確率が42%だが、地球温暖化が2℃を超える確率がわずか2%になることを明らかにしている。一方、温室効果ガス排出量の削減を2029年まで先延ばしした場合には、SSP2-4.5シナリオ(炭素排出量が21世紀半ばまで高い水準を保ってから減少し始める)の下では、1.5℃の温暖化が不可避となる確率が66%に上昇することも明らかになった。この66%という確率は、全ての排出シナリオの下での2027年から2032年までの予測に示された。SSP2-4.5シナリオの下では、地球の温暖化が1.5℃や2℃のレベルに達する4~6年前にこうした温暖化が不可避となると予測されている。


There is a 42% probability that the world may already be committed to at least 1.5 oC of warming relative to pre-industrial temperatures, even if emissions are halted immediately, according to a modelling study published in Nature Climate Change. This probability rises to 66%, however, if emissions are not cut until 2029, emphasizing the need for immediate action to avoid committing to peak levels of warming.

The atmospheric lifetime of greenhouse gases dictates the longevity of their impact after emissions are ceased. Therefore, an understanding of the unrealized warming that will take place due to past emissions is needed in order to assess the likelihood of limiting global warming to the targets set in the Paris Agreement.

Michele Dvorak and colleagues use an emissions-based climate model to understand committed warming — the knock-on effect of previously emitted greenhouse gases — under current, as well as alternative, emissions mitigation pathways (the Shared Socioeconomic Pathways (SSPs) as used in the IPCC AR6 report) between 2021 and 2080. The authors reveal that if emissions were halted immediately, there is still a 42% probability that the world will be committed to exceeding 1.5oC of warming, however only a 2% probability that warming will exceed 2 oC. Leaving emissions cuts until 2029 — under a SSP2–4.5 scenario in which carbon emissions remain high until the middle of the century before starting to decline — increases the probability of commitment to 1.5 oC of warming to 66%. This probability is mirrored in predictions between the years 2027 and 2032, across all emissions scenarios. For SSP2–4.5 scenarios, the world is predicted to reach the levels for committed warming four to six years before those temperatures will be experienced.

This research highlights the need for urgent mitigation to avoid committing to higher levels of warming and other associated changes in the climate system in the future.

doi: 10.1038/s41558-022-01372-y


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