At COP24, climate consensus reigns. But what does that really mean?
| Boulder, Colo.; and Katowice, Poland
As leaders from around the world gathered in Poland for start of the United Nations鈥� annual climate change conference, the scientific consensus underpinning our understanding of global warming and its听likely effects through the coming years and decades is a key backdrop.
The 24th Conference of the Parties to the United Nations Framework Convention on Climate Change, known as COP24, comes just a couple months after from the UN鈥檚 Intergovernmental Panel on Climate Change, focusing on the consequences of exceeding 1.5 degrees C (2.7 degrees F.) of warming.
And just over a week ago, the US government released Volume 2 of its 鈥� a major body of work that involved input from 13 agencies and some 300 scientists, and that outlines impacts, risks, and adaptation in the United States.
Why We Wrote This
For some people, acceptance of climate change comes down to belief. But for the majority of the nations gathering for COP24, it is a matter of scientific consensus, the product of a cumulative and rigorous body of research.
Both documents represent the most authoritative and comprehensive summary of current climate science. And both paint a picture of an increasingly urgent problem.
But just what does consensus mean in a scientific sense? Some scientists worry that the public鈥檚 misunderstanding of scientific terms like 鈥渃onsensus,鈥� 鈥渢heory,鈥� and 鈥渦ncertainty鈥� contributes to many misperceptions, amplifying disagreements and casting unmerited doubt.
鈥淭he word 鈥榗onsensus鈥� is a misleading word, because it is implying there is a negotiation about scientific outcome, and that is absolutely not true,鈥� says Pavel Kabat, chief scientist and research director for the World Meteorological Association, as he prepares for a discussion at the UN conference hall at the 鈥淪podek鈥� (saucer) arena, an iconic landmark of Katowice and one of the most recognized architectural objects in Poland.
Science doesn鈥檛 negotiate, Dr. Kabat notes. Instead, the process that goes into creating something like the IPCC report he thinks can be better understood as a 鈥渟ynthesis of the state of the knowledge.鈥�
When the US government released the latest National Climate Assessment on Nov. 23, a day after Thanksgiving, skeptics jumped on it, claiming it overplayed scientific certainty, relied on imperfect models, or was 鈥渂ased on the most extreme model scenario,鈥� as White House press secretary Sarah Huckabee Sanders put it.
President Trump鈥檚 response to the report 鈥� which is mandated by law 鈥� was even more succinct: 鈥�,鈥� he told reporters a few days after it was released.
And this week, even as the world鈥檚 largest climate forum kicked off, Trump formalized his withdrawal from the international political consensus, making the US the only country at the Group of 20 summit of the world鈥檚 industrialized economies in Argentina not to sign a joint statement on climate change until a special clause was added reaffirming the US plan to withdraw from the Paris climate agreement.
But that sort of rhetoric, say scientists, contributes to widespread misunderstanding about just how certain scientists are.
鈥淚 think part of people鈥檚 discomfort with this is that they think it鈥檚 the same as, you know, 鈥榮cientists say coffee is good for you; scientists say coffee is bad for you; scientists say this, scientists say that,鈥� 鈥� says Katharine Hayhoe, director of the Climate Science Center at Texas Tech University and the lead author of Chapter 2 in the assessment.
While there鈥檚 always something new to learn about complex atmospheric and climate processes, says Dr. Hayhoe, the fundamental principles behind global warming are both basic and well understood.
鈥淭hat science is so old and so basic that to deny that science, we would have to be denying basic thermodynamics that explains how our refrigerators and our stoves work and basic nonlinear fluid dynamics that explains how airplanes fly,鈥� she says. 鈥淎nd there鈥檚 not a lot of politicians and pundits claiming that airplanes don鈥檛 fly or that stoves don鈥檛 heat and refrigerators don鈥檛 cool.鈥�
Getting to consensus
Hayhoe and other scientists involved in state-of-the-science reports describe a process that involves hundreds of scientists, multiple reviews, public comments, and total transparency. For the most recent volume of the National Climate Assessment, each of the 29 chapters had lead writers and contributing writers 鈥� all experts in their field 鈥� who made sure they felt comfortable with everything in the chapter. In addition to comments from all authors and multiple federal agencies, the draft went through extensive public review and review by the National Academy of Sciences. Anyone from the public was invited to download and comment on the draft, and authors had to respond to every single comment on the record.
鈥淗ow much more transparent can you get?鈥� asks Hayhoe.
Indeed, rather than feeling like they鈥檙e stretching the boundaries of what scientists feel confident about, or looking at 鈥渕ost extreme model鈥� scenarios, many scientists worry that these reports often downplay the risks or are too conservative.
Donald Wuebbles, an atmospheric scientist at the University of Illinois who was the lead author of , released last year, notes that in some instances authors of that report scaled back proposed statements to accommodate听the views of more temperate scientists.
鈥淥ne of the things that happens here is that, because you really want to reach a consensus, these reports tend to be very conservative,鈥� says Dr. Wuebbles. 鈥淪o when we make a strong statement 鈥� when we say it鈥檚 鈥榲ery likely,鈥� greater than 95 percent certainty, that something is happening 鈥� my God, that pretty much says it鈥檚 happening.鈥�
And, as with 鈥渃onsensus,鈥� Wuebbles and others note that the public doesn't necessarily understand what听鈥渦ncertainty鈥� means in scientific terms.听In science, it鈥檚 a quantifiable measurement of data variability, and is always present to some extent.
鈥淲e use models all the time for developing cars and airplanes and all kinds of other things on our planet, and those models aren鈥檛 exact either. They have uncertainties in them,鈥� says Wuebbles.
A 鈥榣ively process鈥�
Some critics of big reports like those from the IPCC or the national assessments have charged that they end up being a sort of 鈥済roupthink鈥� process where dissenting voices get filtered out. It鈥檚 a claim that the scientists most intimately involved push back against strongly.
鈥淚t鈥檚 a very lively process. It鈥檚 really hard for scientists to agree,鈥� says Valerie Masson-Delmotte, research director at the French Alternative Energies and Atomic Energy Commission, speaking near the IPCC pavilion in Katowice. Dr. Masson-Delmotte has contributed to several IPCC reports, and says she often encounters misperceptions about the process: that scientists vote on the findings, for instance, or that they 鈥渃ount papers that agree or disagree.鈥�
Scientists tend to approach the process with critical minds, she says, and with a lot of discussion about potential knowledge gaps or limits to knowledge. And diversity 鈥� of scientific background, and country of origin, and age 鈥� can make the process even more robust.
鈥淚t makes it better when you don鈥檛 work in silos,鈥� says Masson-Delmotte. 鈥淭he outcome is much more rigorous when you have more diversity in the chapter teams.鈥�
Of course, none of this means that climate science 鈥� or any science 鈥� is 鈥渟ettled.鈥� While big reports emphasize what is known, and where scientists agree, most scientists spend the bulk of their time working on what is unknown, and where they don鈥檛 agree. There are plenty of uncertainties with climate change, particularly when it comes to economic costs, localized effects, or the connection to weather events.听The big synthesis reports try to make those uncertainties as clear as possible.
And each new iteration of these reports adds to and revises previous analyses, as modeling gets stronger and data and observations are added.
Looking at the changes in sea level predictions from the first IPCC report to the fifth is one example, says Masson-Delmotte. 鈥淵ou can see how satellite measurements have changed the way we look at ice sheets.鈥� Satellite observations, she says, showed fast-flowing ice streams that altered scientists鈥� previous ideas. 鈥淏ecause you have new observations, you understand better the formation of ice,鈥� she explains. 鈥淚t鈥檚 not yet fully completely understood and modeled, but it changed the way people see ice sheets completely.鈥�
Acknowledging mistakes
Sometimes, scientists do get things wrong. A听 published in Nature this fall that indicated oceans were warming faster than scientists had believed made news both when it was published, and then when an independent researcher discovered errors in the study that made the conclusions seem more certain than they were.
The report鈥檚 authors acknowledged the errors, apologized, and are working to correct them;听though they emphasize that they 鈥渄o not invalidate the study鈥檚 methodology.鈥�
It was a mistake jumped on by many skeptics, but 鈥渋t鈥檚 very much part of the scientific process,鈥� notes Wuebbles, adding that outlier results are never enough to change what the state of the science is.
Hayhoe also notes that she sees some irony in the fact that, several years ago, she was a co-author that closely examined 38 contrarian papers that disputed anthropogenic warming.
鈥淲e found every single one of those studies had an error in them ... that if it was corrected brought their results in line with the scientific consensus,鈥� says Hayhoe. And yet, she says it was hard to get any interest in study, because people said 鈥渋t鈥檚 not new science.鈥�
In some ways, the process of assembling big, state-of-the-science consensus reports is the opposite of what most scientists do in their regular work, trying to generate new knowledge. But scientists say that process of laying out consensus is still critically important, especially for policymakers. The international assessments on stratospheric ozone were a key piece of getting the Montreal Protocol passed in 1987, says Wuebbles, citing an agreement that is widely credited with shifting the tide of ozone depletion.
And with something that has become deeply politicized, like climate change, Hayhoe emphasizes that most skeptics don鈥檛 try to refute accepted facts so much as sow disinformation about the level of uncertainty.
鈥淭hey understand that they don鈥檛 have to convince people that [climate change] isn鈥檛 real. All they have to do is convince people that we don鈥檛 know, and that is sufficient to delay action,鈥� she says. As a result, she says scientists need to shift how they communicate with the public, focusing about 90 percent of their communication on what they know. 鈥淲e know it鈥檚 real. We know it鈥檚 us. We know the impacts are serious and even dangerous. We know our choices matter. And what we don鈥檛 know is the potential unpleasant surprises that may result from our inadvertent but unprecedented experiment with the only home that we have.鈥�
This story was produced with support from an听Energy Foundation grant to cover the environment.
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