IPCC’s next major climate assessment »Yale Climate Connections

John Kerry – then U.S. Secretary of State, and now future U.S. special envoy for climate – signed the Paris Agreement on Climate Change on April 22, 2016, at UN headquarters, with his granddaughter. The next IPCC Sixth Assessment Report will be released before the 2023 deadline for nations to update the broadcast reductions they promised under the agreement. (Photo credit: United Nations / Flickr)

Despite the rapid impact of the COVID-19 pandemic, the Intergovernmental Panel on Climate Change is making progress towards the end of its Sixth Assessment Report, the latest in a series begun in 1990.

The IPCC estimates, produced by many hundreds of scientists volunteering countless hours, have long been the world’s most definitive statements about human induction of climate change due to fossil fuel use. Rather than conducting its own research, the IPCC draws up its consensus evaluation reports based on the extensive set of peer-reviewed work in scientific journals. The project reports are examined by experts and officials in UN member governments before they become final.

It is too early to know exactly what the authors will conclude in the Sixth Assessment Report (AR6), due out in 2021-22, but the chapter sketches suggest a more intertwined look at how society is affected by climate and how it reacts to it. crisis.

The report could also tilt its hat to a narrow range of possible outcomes, as reflected in recent key articles and trending greenhouse gas emissions. If the most horrific scenarios of past reports are a little less likely than it seemed a decade ago, some of the more tame scenes could be increasingly unattainable.

Nations will use the new assessment as they prepare to revise their emissions targets in the first five-year provision of the Paris Agreement, set for 2023.

Like most of its predecessors, AR6 will appear in four volumes: one focused on physical science (Working Group I or WGI); another on adaptation and vulnerability to climate change (WGII); third on mitigation (WGIII), or reduction of greenhouse gas accumulation; and a final synthetic report.

The WGI volume of this estimate was originally linked to appear in April 2021, followed by WGIII in July (before WGII ​​in October) and a summary report in May 2022. These dates appear to have changed by a few months as a result of the COVID -related interruptions.

The first five IPCC estimates were spaced around five to six years old, with the most recent published in 2013-14. That left little time for scientists to breathe their collective breath between reports. This time the schedule allowed eight years between major estimates.

“Scientists have long argued for more time between estimates, so I think that gap between AR5 and AR6 is a good thing,” said climate researcher Red Knutti (ETH Zurich), who contributed to the third, fourth and fifth assessment reports.

“More time also means there can be tighter integration between the working groups.”

Delegates of Sierra Leone
Two Sierra Leonean delegates meet at an IPCC meeting in Copenhagen, Denmark, on 30 October 2014. (Photo credit: IPCC through IISD Reporting Services).

During the interval between AR5 and AR6, the panel issued three special reports, including one on oceans and ice and another on terrestrial effects. The other was “Global Warming of 1.5 ° C,” which hit a bomb in 2018. Its extreme conclusion: the world needs to reduce more than half of its greenhouse gas emissions by 2030 to conserve two-thirds chances of limiting warming to 1.5 degrees Celsius.

Calling the work of IPCC thoroughly is an understatement. For these three special reports alone, IPCC authors evaluated about 20,000 publications and processed about 100,000 comments from more than 2,500 reviewers, noted IPCC President Hoesung Lee.

Susan Solomon
In this 2010 file photo, atmospheric chemist Susan Solomon – then based at NOAA – shows the two-part draft of the IPCC’s Working Group I report for the Fourth Climate Assessment. Solomon co-chaired the WGI of that assessment along with glaciologist Qin Dahe of the China Middle Engineering Institute of Cold and Arid Regions. (Photo credit: Bob Henson)

Increases progress

As a sculptor scrapping to display a statue, each IPCC assessment has led to a more detailed picture of the climate crisis, even as the vast majority of fundamental science remains sound.

With AR6, the enhanced cooperation between working groups will support more emphasis on solutions, as befits a world where climate action is considered more urgent than ever by a growing range of stakeholders.

Cities that are clearly vulnerable to climate as well as solvable are a particular focus of the new report. When the IPCC released its first assessment report in 1990, about 43% of the world’s 5.29 billion people lived in urban areas, according to Our World in Data. Since then there has been a titanic balance from country to city. As of 2017, urban areas accounted for about 55% of the 7.53 billion people on Earth.

Another recent context: emission growth has slowed in recent years more than one might think. Carbon dioxide emissions grew by 29% in the decade before the 2013 estimate, but they grew by only about 5% from 2013 to 2019, according to the Global Carbon Project. Key factors include coal depletion and increased energy efficiency measures.

CO2 emissions are projected by the Global Carbon Project to decline by around 7% in 2020 in response to COVID’s economic success, particularly in terms of transportation. The new assessment will look at the effects of lower emissions on climate and air quality, based on egg-laying from recent research. Chris Jones (UK Met Office) coordinated a comparative project to see how climate models used in the new assessment respond to this year’s emissions fall.

Going forward, the touching question is to what extent (or not) emission cuts will be prioritized as the world shifts to economic recovery. If the 60% -counted-to-2030 achievement is met, then the 2020s will have to see average emission reductions annually equal to the decrease in COVID in 2020 – indeed a high order. A fall close to this magnitude, with net zero CO2 emissions by the 2050s, would be consistent with RCP1.9, the most optimistic of the seven emission pathways of the new assessment (more than four in the last cycle).

The highest path, RCP8.5, has often been considered “usual,” but with recent emission trends, it now looks more like a worst case scenario. The next assessment will include RCP8.5 as well as RCP7.0, a newly created roadway designed to capture the “medium to high end of the range of future emissions and warming,” according to Zeke Hausfather (Carbon Brief).

Joyce Coffee, a Chicago consultant who has long worked with cities on climate plans, finds value in keeping high-quality scenarios as a barrier to preventing society from going into climate chaos. “In the event of a local government decision on critical infrastructure built for the long term, hope will not save lives, but realism could,” Coffee said.

Narrowing sensitivity

The ultimate range of warming expected from carbon dioxide doubling, also known as climate sensitivity, was the same in almost every IPCC estimate: 1.5 ° C to 4.5 ° C, a range first presented in a 1979 report led by Jule Charney (Massachusetts Institute of Technology).

Recent studies have begun to empty this territory, including a synthetic article last summer in Reviews of Geophysics led by Steven Sherwood (University of New South Wales Sydney). This comprehensive analysis emerged with a probable range of 2.6 ° C to 4.1 ° C, discarding the lower third of the Charney Mountains based on past century-plus climate as well as the longer-lasting paleoclimate record and reaction processes.

At the same time, a new generation of climate models developed before AR6 includes some with a particularly higher sensitivity than in the past. This increase – not fully understood, and still controversial among scientists – is just one of the complications the new assessment will have to reveal.

“This time a huge issue for IPCC is whether and how they are using new sensitivity information to change the sample distribution that is received from a set of models,” Sherwood said. “If they do it right, it will be a big advance for IPCC.”

Making it real and feasible

Other highlights of the new assessment:

More emphasis on regional weather and climate extremes. A new chapter in the WGI report will highlight the rapidly growing research that links particular weather events to climate change, such as analyzes of the World Weather Attribution project. Another chapter will examine what the various emission pathways can tell us about regional change.

One emerging tool since the last assessment is “large ensembles,” or multiple runs of the same climate model using slightly different starting point conditions, similar to the current commonalities in weather forecasting. Using these sets, scientists can better visualize the range of possible regional climate trends – which is still staggeringly large in some places and more consistent in others, due to natural climate variability that differs by region.

“The power of [large ensembles] for climate impact risk assessment and decision making are largely unused, ”said climate scientist Clara Deser (National Center for Atmospheric Research, or NCAR) in a recent comment for Earth’s Future magazine.

More attention to climate equality. The WGII ​​report, traditionally in two sections, will dedicate a new third section on pathways to sustainable development. It will address adaptation regimes, such as diversified and transformed economies, that can reduce inequalities by improving overall well-being.

A more intertwined approach to the WGI and WGII ​​reports, along with the enhanced regional emphasis, will take “a huge step forward in providing not only policy issues, but effectively feasible climate information,” according to Friederike Otto, associate director of the University. from Oxford’s Environmental Change Institute and lead author of WGI.

A closer look at the demanding side of climate change. The WGIII report will include a new chapter on how social needs and desires can drive or prevent emissions. A range of notable factors include affordability, access to services, social acceptability of climate solutions and environmental skipping – development regimes that pass fossil fuels to more climate-friendly ones, such as using solar energy to give resource-poor residents their first access to electricity.

Solar workers
Workers install solar panels at a health clinic in Rwanda, where the government aims to increase electricity access from 30% to 100% by 2024. (Photo credit: Sunepi / USAID, Walt Ratterman / Flickr)

Thirty years seeking consensus

The huge impact of the IPCC estimates was recognized by a peace prize in 2007, jointly given to the panel and to climate champion and former vice president Al Gore. Each IPCC assessment, in turn, depends on the work of individual scientists who have been working for years to find common threads in the ever-expanding carpet of climate-related research.

To his knowledge, Gerald Meehl of NCAR is the only scientist to have volunteered for all five first IPCC assessments. Meehl is resting this time, but his belief in the value of the IPCC process is unflinching.

“I’ve always said that IPCC is like science olympics,” Meehl said. “The authors all represent their respective countries, and you come together in the spirit of trying to do the right thing, to adjust science, in a mutual support effort.

A brief overview of a new IPCC report on ocean and ice risks

Scientists are usually fierce competitors to each other, but it’s a completely different college experience for IPCC, which puts you in a very positive mood. “


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