Monday , November 30 2020

Factcheck: Are 3-5C of Arctic heating now & # 39; locked in & # 39 ;?

ONE new UN Environmental Report The Arctic was released last week, which included a wide range of changes in the region's climate, environment, wildlife and epidemiology.

The companion Press release focused on the report's section on climate change. It warned it, "though Paris Agreement the targets are met, the Arctic winter temperatures will rise 3-5C by 2050 compared to the 1986-2005 levels "and will warm 5-9C in 2080.

The report was covered by a number of news stores, including Guardian. wired. Tray. CBC and others. Media coverage focused on the idea – promoted in the press release – that large amounts of arctic warming are "locked in", "inevitable" or "inevitable".

A Carbon Brief study, however, has shown that the section of the Climate Change Report is incorrectly in conflict with the objectives of the Paris Agreement – which is to limit heating to "Well below" 2C at the end of the century compared to pre-industrial levels – with a scenario that has much more modest emission reductions that result in about 3C of global warming.

In the climate model, a scenario-limiting global warming runs below 2C, the arctic becomes warmer than the rest of the world. However, the future Arctic winter warming will be around 0.5-5C in the 2080s compared to the 1986-2005 levels, much lower than the 5-9C values ​​stated in the report.

This means that much of the future warming in the Arctic will depend on our emissions during the 21st century, rather than being "locked in" as claimed in the report.

Incorrect section

The UN Environmental Report has the title "Global linkages: A graphic look at the changing arctic". It gives a short, accessible and infographically heavy look at a number of different areas where the Arctic has changed over the past few decades and can change in the future.

The section of the report on Arctic temperatures – which is only two pages long – does not show any new research. Rather, it summarizes the results of a number of recent, more technical studies. Future temperature projections, which were the focus of the press release and associated media coverage, can be found in a single section of the report:

"Warmer temperatures in the Arctic resulted in a record low winter consumption between the ice in 2015-2018 (Overland et al., 2018). In fact, projected temperature changes for the Arctic during a medium or high emission scenario will follow a winter warming trend that is at least twice as high as the northern hemisphere (AMAP 2017a). This means that even though the countries manage to reduce greenhouse gas emissions to the targets outlined in the 2015 Paris Climate Change Agreement, the winter temperatures in the Arctic will still be 3 to 5C higher in 2050 and 5 to 9C higher in 2080 compared to 1986 – 2005 levels. In fact, even though we stopped all discharges overnight, the winter temperature in the Arctic will still increase by 4 to 5 C compared to the late 20th century. This increase is locked into the climate system of greenhouse gases already emitted and ocean heat storage (AMAP 2017a). "

But this section contains a number of unclear statements and errors that suppress the announcement that large amounts of future Arctic heating are "locked into the climate system".

While the first two sentences are correct, problems begin in the third, when the report claims that compliance with Paris collective agreements will still result in winter Arctic warming of 3-5C by 2050 and 5-9C by 2080 compared to the 1986-2005 levels. .

The reference to these figures is 2017 Arctic Monitoring and Assessment Program (AMAP) report. In the 2017 AMAP report, it states:

"Over the Arctic sea, which is ice-free early in winter in some models and covered in thin ice in the late winter, warming is 3-5C in the middle of the century and 5-9C by the last century under RCP4.5."

The UN's environmental report rejects the reference to the Arctic with reference to these heating forecasts as "winter temperatures in the Arctic" – a much larger area of ​​the earth than just the region over the Arctic sea. The actual heating in RCP4.5 for the full Arctic (between 60N and 90N) in the 2017 AMAP report is slightly lower: about 3.8-7.8C in the 2080s. There is another minor problem where the new report gives specific years (2050 and 2080), while the 2017 AMAP report actually uses the periods from 2050-2059 and 2080-2089.

Word list

RCP4.5: The RCPs (Representative Concentration Paths) are scenarios for future concentrations of greenhouse gases and other forcings. RCP4.5 is a "stabilization scenario" where policies are put in place, so atmospheric CO2 concentration levels … Read more

The main problem with the play comes when it connects the 2017 AMAP heating numbers – referring to the RCP4.5 scenario – to "the goals outlined in the 2015 Paris Agreement on Climate Change".

In the Paris Agreement, countries set a target to limit heating "well below" 2C, with a desire to limit heating below 1.5 ° C. However, the 2017 AMAP report deals with only two future emission scenarios: a very high emission RCP8.5 scenario where the world is experiencing more than 4C warming; and a medium-emission RCP4.5 scenario where the world is experiencing around 3C warming over pre-industrial levels at the end of the century.

Word list

RCP2.6: The RCPs (Representative Concentration Paths) are scenarios for future concentrations of greenhouse gases and other forcings. RCP2.6 (also sometimes referred to as "RCP3-PD") is a "peak and decline" scenario where severe counteracting … Read more

If countries were to meet the Paris Agreement's goal of limiting heating to "well below" 2C, global emissions would actually follow an RCP2.6 scenario (or reduce emissions even faster to limit heating to 1.5 ° C). While RCP2.6 still sees an extra arctic warming, it is much smaller than the figures in the report.

The figure below shows winter warming in the Arctic from all of them CMIP5 climate models used in the Intergovernmental Panel on Climate Change (IPCC) fifth assessment report for the RCP2.6 scenario. The black lines show the average of all models, the dark area shows the area where two-thirds of the models fall (the one-sigma range), and the light area shows the area covering 95% of the model run (the two-sigma range).

The RCP2.6 climate model runs from CMIP5 to the region between 60N and 90N for the winter months (December, January, and February) for the 32 different climate models that provide RCP2.6 runs (with one run used per model). Model data obtained from KNMI Climate Explorer.

In a scenario where the Paris Convention's objectives are met, the actual winter warming expected for the Arctic is 0.8-4.5 ° C in the 2050s and 0.5-5 ° C in the 2080s in compared to 1986-2005 (following the approach used in the 2017 AMAP report from giving one-sigma areas). The multi-model value shows 2.8 C heating both in the 2050s and 2080s as falling global emissions limit further heating after the mid-century.

The statement in the report that "even though we stopped all discharges overnight, the winter temperatures in the Arctic will still increase by 4C to 5C compared to the late 20th century" is puzzling as it does not appear anywhere in the 2017 AMAP report that it cites.

Worryingly, the UN Environmental Report claims that cutting emissions to zero will immediately lead to more warming than occurs in climate models running the RCP2.6 scenario – a scenario that has zero emissions only around 2080. The Carbon Brief reached a number of climate scientists who all expressed amazement at what might form the basis of this claim. The Carbon Brief requested the UN Environment and the report's authors for an answer but did not receive one before publication. (This article is updated to include any answer.)

According to for an analysis highlighted in the recent IPCC special report of 1.5 C, all human emissions of greenhouse gases and aerosols reduce to zero at the same time a modest short-lived shock in global temperatures of about 0.15 C, as earth-cooling aerosols disappear, followed by a decline. About 20 years after the emissions went to zero, global temperatures will fall below today's levels and then cool by about 0.25 C at 2100. While aerosol reduction may have a greater warming effect in the Arctic than other regions, a further prolonged warming of 4C to 5C seems somewhat unlikely.

Not & # 39; locked in & # 39;

Why can the report summarize a 3C global warming scenario (RCP4.5) with the Paris agreement goal (RCP2.6)? The actual obligations of the countries of the Paris Agreement – it nationally defined contributions (NDC's) – falls well short of what would be needed to meet the Paris objective. If countries only take these actions – and don't ratchet up their commitments after the Paris commitment end in 2030 – studies suggest that the world would be on the right track slightly more than 3C heatingalthough much depends largely on assumptions about emissions between 2030 and 2100.

But even though the report meant that "the warming implicated in the existing Paris commitments" rather than the "Paris goals", the press release and subsequent media coverage are still misleading. Unless the authors argue that the world as a whole is already locked in 3C warming – and there is lots of scenarios That will keep global warming below 2 ° C or even up to 1.5 ° C warming – the amount of future warming that will occur in the Arctic during the 21st century depends largely on our future emissions.

The figure below shows the winter's Arctic warming compared to 1986-2005 from the average of all IPCC CMIP5 climate models for each future RCP emission scenario. There is a wide range of potential future warming, from as little as 2.7 C in 2100 in RCP2.6 to as much as 12C in RCP8.5. Which of these future warming scenarios will largely depend on our greenhouse gas emissions for the rest of the 21st century.

CMIP5 Multimodel means for each RCP scenario for the region between 60N and 90N for the winter months (December, January and February). Model data obtained from KNMI Climate Explorer.

If the world actually meets the Paris goal of limiting heating below 2C, the future Arctic winter warming will be about 0.5-5C, much lower than the 5-9C values ​​listed in the report.

There is still a wide range of possible results for the region. As a result, any requirement that massive amounts of future heating for the region be "locked in" is misleading.

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