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‘Rare, Happy News’ from Climatologists: Worst-Case Warming Now ‘Increasingly Implausible’

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It doesn’t make the climate crisis any less urgent, but there’s a growing view among scientists that humanity’s decarbonization efforts so far have dodged the worst climate outcomes projected in the last global assessment report in 2014.

From scientists publishing in the journal Nature, to one of the world’s self-described climate “alarmists” writing for New York Magazine, multiple sources are celebrating the strong likelihood that RCP8.5, the extreme scenario from the Intergovernmental Panel on Climate Change (IPCC) that projects 5.0°C average global warming by 2100, won’t likely come to pass.

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“Happily—and that’s a word we climatologists rarely get to use—the world imagined in RCP8.5 is one that, in our view, becomes increasingly implausible with every passing year,” write [2] Zeke Hausfather, director of climate and energy at the Breakthrough Institute in Oakland, and Glen P. Peters, research director at Oslo’s CICERO Center for International Climate Research, for Nature.

“Assessment of current policies suggests that the world is on course for around 3°C of warming above pre-industrial levels by the end of the century—still a catastrophic outcome, but a long way from 5°C,” they add. “We cannot settle for 3°C; nor should we dismiss progress.”

“Over the last few weeks a new narrative about the climate future has emerged, on balance encouraging, at least to an alarmist like me,” added [3] columnist and literary editor David Wallace-Wells in mid-December. “As best as we can understand and project the medium- and long-term trajectories of energy use and emissions, the window of possible climate futures is probably narrowing, with both the most optimistic scenarios and the most pessimistic ones seeming, now, less likely.”

Hausfather and Peters trace the shift in perspective to a choice that climate scientists and energy modellers made nearly a decade ago, in the lead-up to the IPCC’s Fifth Assessment Report (AR5) in 2014, producing consequences that are now “hotly debated” as the IPCC’s next big report moves into its final stages this year.

In the lead-up to AR5, “researchers developed four scenarios for what might happen to greenhouse gas emissions and climate warming by 2100,” the two authors explain. “They gave these scenarios a catchy title: Representative Concentration Pathways (RCPs). One describes a world in which global warming is kept well below 2°C relative to pre-industrial temperatures (as nations later pledged to do under the Paris climate agreement in 2015); it is called RCP2.6. Another paints a dystopian future that is fossil fuel-intensive and excludes any climate mitigation policies, leading to nearly 5°C of warming by the end of the century. That one is named RCP8.5.”

That scenario was only ever intended to explore “an unlikely high-risk future,” they add. “But it has been widely used by some experts, policy-makers, and the media as something else entirely: as a likely ‘business as usual’ outcome. A sizeable portion of the literature on climate impacts refers to RCP8.5 as business as usual, implying that it is probable in the absence of stringent climate mitigation. The media then often amplifies this message, sometimes without communicating the nuances. This results in further confusion regarding probable emissions outcomes, because many climate researchers are not familiar with the details of these scenarios in the energy modelling literature.”

Particularly when coverage and scientific reporting are built around RCP8.5 and RCP2.6, the “focus becomes the extremes,” they add, “rather than the multitude of more likely pathways in between.”

Contrary to that communications cascade, Hausfather and Peters look at today’s emissions trends, and they like some of what they see. “Emission pathways to get to RCP8.5 generally require an unprecedented, five-fold increase in coal use by the end of the century, an amount larger than some estimates of recoverable coal reserves,” they write. “It is thought that global coal use peaked in 2013, and although increases are still possible, many energy forecasts expect it to flatline over the next few decades.” And meanwhile, “the falling cost of clean energy sources is a trend that is unlikely to reverse, even in the absence of new climate policies.”

Hausfather’s and Peters’ conclusions aren’t unanimous within the climate science community: they note that some scientists see “feedback” effects, like greenhouse gases released from thawing permafrost, that are understated in the most recent generation of IPCC climate models and could pull the Earth back to an RCP8.5 pathway.

But “in our view, reports of emissions over the past decade suggest that they are actually closer to those in the median scenarios,” they write. “We contend that these critics are looking at the extremes and assuming that all the dice are loaded with the worst outcomes.”

“Asking ‘what’s the worst that could happen?’ is a helpful exercise. It flags potential risks that emerge only at the extremes,” they add. But “we must all—from physical scientists and climate impact modellers to communicators and policy-makers—stop presenting the worst-case scenario as the most likely one.” That’s because “overstating the likelihood of extreme climate impacts can make mitigation seem harder than it actually is,” and “this could lead to defeatism, because the problem is perceived as being out of control and unsolvable. Pressingly, it might result in poor planning, whereas a more realistic range of baseline scenarios will strengthen the assessment of climate risk.”

With the latest generation of climate models just recently published, the two authors suggest three steps the climate community can take in the next year before the IPCC publishes its Sixth Assessment Report, AR6:

• Explore the “space between the high-end and low-end scenarios” more deeply, and communicate the range of likely climate impacts more clearly;

• Recognize that different users need different modelling tools, and use the final AR6 synthesis to integrate those various perspectives on climate risk;

• Use “more plausible outcomes” in the multitude of climate impact studies that will flow from AR6. “When RCP8.5 or its successor SSP5-8.5 are deployed,” Hausfather and Peters write, “they should be clearly labelled as unlikely worst cases rather than as business as usual.”

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11 Comments To "‘Rare, Happy News’ from Climatologists: Worst-Case Warming Now ‘Increasingly Implausible’"

#1 Pingback By ‘Rare, Happy News’ from Climatologists: Worst-Case Warming Now ‘Increasingly Implausible’ – Enjeux énergies et environnement On February 3, 2020 @ 1:13 AM

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#2 Comment By Nathan Brett On February 3, 2020 @ 2:14 PM

I’m happy to see a good news story, but worried that it may be misleading. There seems to be some confusion here about the phrase “business as usual” (BAU) and a continuation of the practice of ignoring feedback effects. First, as most people it, BAU does not include working to mitigate the effects of climate change. But because this mitigation activity is now a significant part of our current practices, the authors of “Rare, Happy News…” build this into their critique of the previous IPCC worst case scenario. While it is unlikely that humans will just do nothing in the face of the dire warnings of scientists, it is confusing to build world-wide efforts to change into a statement of the worst case. Second, ignoring or underestimating effects of the multiple feedbacks involved, is ignoring the heart of the problem. IPCC projections have consistently underestimated the speed of warming, largely because of this. To take one Canadian example of feedback from generally ignored: the CO2 released by the forest fires in BC in 2017 and 2018 (each bigger than PEI) was several times greater than the entire amount released by the consumption of fossil fuels in BC. One can only image the GHG footprint of this year’s fires in Australia.

#3 Comment By Peter On February 3, 2020 @ 2:34 PM

This is utter bollocks as disinformation at its’ worst being perpetuated by what was once a reputable journal.

#4 Comment By Peter Tang On February 3, 2020 @ 3:18 PM

MAKING PROGRESS BUT NEED TO CONTINUE TO GO GREEN FOR A CLEANER HEALTHIER AND LONGER LIFE ON PLANET EARTH.

#5 Comment By Ruth Pickering On February 3, 2020 @ 6:45 PM

Well, it seems to me that this is an overly optimistic view of ‘business-as-usual’. If emissions from fossil fuels were levelling off, one might find solace in this article. However, everything I read indicates that fossil fuel extraction is expanding,: more pipeline approvals and increasing subsidies for fossil fuels Hopefully not imminent, but very possible, is the approval of the Tech Frontier Tar Sands Mine, intended to extract until 2076!
Maybe these scientists believe business-as-usual is a flat line.
The current reality is rapidly increasing fossil extraction. and fracking for massive LNG plants (which will continue releasing dangerous GHGs (methane) emissions as they are built to last well past 2050.
Until we stop the rapid increase in fossil fuel emissions, there is no way we can be assured of a livable planet. Because we can’t be at all sure that some or all of the possible ‘positive’ feed-back loops will not occur, we can’t predict any good news! Right now one of the largest Antarctic icebergs is melting very rapidly because a previously unknown phenomenon has recently been discovered that is melting it from underneath! When it melts it will significantly increase an unexpected early rise in sea level.
And how about the continuing loss in the expected ‘carbon sinks’ of the Canadian Boreal forests ( from Tar Sands mining), the intentional burning of the Amazon, Australia’s recent bush fires and an expected next round of fires in Alberta’s forests? All of these increase emissions and decrease the carbon sink of healthy trees that we have been counting on for capturing Carbon.
Any unjustified optimism further offers comfort to the governments that are stalling on real climate action (like our very own Canada), reduces pressure on the five big Canadian banks that continue to finance Fossil expansion and encourage the Fossil Industry to continue expanding!

#6 Comment By Mitchell Beer On February 5, 2020 @ 12:24 AM

Thanks, Ruth. Completely, absolutely agree. The authors we summarized didn’t say this explicitly, but what I thought I took away was that the gain they referred to was a combination of coal closures (which are verging on the epic in many parts of the world) and uptake of renewables. But once again, NOTHING here is suggesting that we’ve gained nearly enough ground, nor that there is any reasonable path forward for oil and gas except a managed decline.

#7 Comment By Gene McGuckin On February 3, 2020 @ 7:50 PM

Happily, the nuclear explosion only destroyed half of the megacity. Happily, the flooding only killed two-thirds of the thousands expected. Happily, the fire victims only lost their arms and legs. Which word doesn’t fit in these sentences?

#8 Comment By Laurie Parkinson On February 4, 2020 @ 2:52 PM

Very comforting to read, and thanks for explaining the RCPs.

Three questions/comments:

1. Are the methane leaks from gas wells/piping/etc included in the Assessments?

2. Is melt from Greenland and the Arctic/Antarctica now included in the Assessments? Carbon emissions from planes & ships, and melting permafrost? I remember reading these weren’t included in 2015.

3. Hard to take this article seriously when I read:
[5]
Comment?

Thank you so much. Laurie Parkinson

#9 Comment By Mitchell Beer On February 5, 2020 @ 12:16 AM

Great questions, Laurie, thanks, especially #3. I spotted that, too, wondered exactly the same thing, and it’s tentatively in our story lineup for next week. I resisted the strong temptation to summarize it sooner, hoping it’ll generate further commentary that answers the question.

On the first two questions — would anyone else care to weigh in?

#10 Comment By Keith McNeill On February 5, 2020 @ 1:42 AM

How is it possible to say that humanity’s decarbonizaton efforts are working when the amount of CO2 in our atmosphere continues to increase at an increasing rate?
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#11 Comment By Mitchell Beer On February 5, 2020 @ 9:32 AM

Keith, I’m reposting my reply from our exchange on Facebook. Just want to say thanks for taking time to post on both platforms!

This post has received a _lot_ of feedback on exactly that point. The authors aren’t saying the job is done, or that the carbon pathway they now think is plausible is anywhere near acceptable. Their point is that if RCP8.5 projected 5.0°C average warming, and 3.0 looks more likely in this moment, we should take heart from that initial, incremental, incomplete progress and treat it as a signal to redouble our efforts. Because in a very preliminary way, those efforts are starting to work…which is not something we hear or think very often.

I’ve been thinking that another way to put it is that things are very bad, and would be that much worse if not for the gargantuan effort so many of us have been putting in to turn the tide. That with the next round of IPCC models, it looks like the plausible pathway will tick up again, and at that point it would have been _worse still_ if not for the coal phaseouts, the divestment, the rise of renewables, and any oil and gas infrastructure anyone has been able to shut down or prevent.

For practical, day-to-day purposes, the answer is still the same: until we can see our way to 1.5°C or lower, without relying on spin, greenwashing, or science fiction, the job isn’t done. But I don’t think we will ever see a single decision, or announcement, or political win that will take us all the way to that endpoint in a single shot! And with the mounting climate despair that _is_ dragging everyone’s efforts down, we made this our lead story Monday because I do believe we all need the good news, too, even though it’s conditional.