In a May 16 Truth Social post, President Donald Trump cited updated climate change scenarios to misleadingly claim that experts had “admitted” prior climate change projections “were WRONG! WRONG! WRONG!” The regularly scheduled revision reflects in part the progress the world has made on moving away from fossil fuels.
Trump was reacting to a new set of seven scenarios of emissions by the end of the century, proposed in an April 7 paper by an international group of scientists. Over time, the range of plausible scenarios has narrowed. The most pessimistic scenario now shows lower emissions than 15 years ago, when the prior scenarios were developed, and the most optimistic one now shows more.
Trump, however, used the update to cast doubt on the reality and seriousness of global warming. “GOOD RIDDANCE!” he wrote. “After 15 years of Dumocrats promising that ‘Climate Change’ is going to destroy the Planet, the United Nations TOP Climate Committee just admitted that its own projections (RCP8.5) were WRONG! WRONG! WRONG!”
RCP8.5 was the most pessimistic of four scenarios that were selected in 2007 and described in 2011. The scenarios looked at how much the climate might change by 2100, relative to the industrial revolution.
“RCP8.5 was always this low-probability, high-impact case,” Detlef van Vuuren, a climate researcher at Utrecht University and PBL Netherlands Environmental Assessment Agency, told us. He helped lead the effort to develop both the new and earlier climate scenarios. As 15 years have passed and the end of the century has gotten closer, it has become clearer what emissions paths are most plausible.
It’s “useful to consider possible outcomes that are less attractive, and it doesn’t mean that you were wrong by considering those if they didn’t come true,” van Vuuren said. “Unfortunately, the overall outcome of all of this is that we are in a situation that is actually leading to quite strong climate impact still.”
Van Vuuren also clarified that Trump is incorrect to call the international group of researchers behind the scenarios “the United Nations TOP Climate Committee.” A U.N. group, the Intergovernmental Panel on Climate Change, summarizes the existing research on climate change. The scenarios are anticipated to have a “major role” in the group’s next climate assessments, he said, but it did not come up with the new scenarios.
“The paper belongs to the broader body of scientific literature produced by the international research community, under the coordination of the World Climate Research Program, not the IPCC,” the IPCC wrote in a May 20 statement.
We asked the White House if Trump was referring to the IPCC in his post and if he was suggesting that climate change is not a serious problem. In an emailed reply, White House spokeswoman Taylor Rogers said that “Dumocrats” and others had for years made “bogus ‘climate change’ claims that we would destroy the planet,” leading countries that pursued energy transition policies to be “destroyed” with “blackouts and sky-high prices.”
“The rogue climate activists continue to be ‘Wrong! Wrong! Wrong!’ and President Trump continues to be ‘Right! Right! Right!’” Rogers said.
Why Climate Scenarios Have Narrowed
Experts said that Trump’s comments on climate scenarios misrepresented their purpose.
“Scenarios are not predictions: they are ‘what-if’ pictures of the future,” Katharine Hayhoe, a climate scientist and professor at Texas Tech University, told us via email.
“The highest-emission scenario serves as a basis for exploring the potential consequences of climate change if everything goes wrong,” a post on the new climate scenarios from the PBL Netherlands Environmental Assessment Agency, a Dutch government research institute, explained. “After all, it is important to ensure that we are also prepared for undesirable developments.”
Termed “representative climate pathways,” the older scenarios by design covered a broad range of climate trajectories, with RCP8.5 representing the 90th percentile of baseline scenarios in the literature at the time. (A baseline scenario illustrates a case where people do not take action to mitigate climate change, but there can be a range of baseline scenarios depending on other factors, such as how much fossil fuel use increases.) The most optimistic scenario, by contrast, represented below the 10th percentile of mitigation scenarios in the literature.
Van Vuuren likened the scenarios to a range of possible times a person might arrive at a destination on a drive. Initially, a person might want to consider the possibility of a traffic jam or other misadventures. But as the trip progresses, a traffic jam will or will not emerge, and the range of plausible arrival times will become narrower. In the case of the climate scenarios, the destination is the year 2100, and we are now 15 years closer to it than we were when the previous scenarios were laid out.
In recent years, the world has not followed the trajectory outlined in RCP8.5, van Vuuren said. There are lower emissions and greenhouse gas concentrations in the atmosphere than were laid out in that scenario. This means that a new low-probability, high-impact case will “automatically” be lower than the previous one, he said.
On top of this, renewable energy became more economically competitive, he said. RCP8.5 assumed high use of fossil fuels, especially coal. When RCP8.5 was developed, “emissions had been growing relatively fast in Asia, and based on coal,” van Vuuren said. In the years since, the outlook has improved for the growth of renewables and gotten far worse for coal.
Between 2000 and 2015, “global emissions and temperature change had been reliably tracking” the RCP8.5 scenario, Hayhoe said.
But since 2015, reality diverged from the RCP8.5 scenario, due to “massive advances” in clean energy, she said, as well as climate policies that were enacted following the 2015 Paris Agreement, a major climate treaty that the U.S. has left during each of the two Trump administrations. “And that, in a nutshell, is why the higher of the new scenarios is lower than RCP8.5,” she said.
As time passed, some climate scientists began to critique the plausibility of RCP8.5, van Vuuren and his colleagues acknowledged in the new paper. Some also argued that it never was all that plausible. And some have said that researchers, policymakers and communicators have at times misused RCP8.5 by treating it as a likely outcome of the business-as-usual approach to climate change.
But Trump and his allies have overgeneralized these criticisms. We wrote in 2018, for example, that Trump administration officials had criticized the National Climate Assessment for being based on the “worst” or “most extreme” scenario, when it had used multiple scenarios.
And last year, a Department of Energy report released to justify rescinding the endangerment finding — the underpinning for greenhouse gas regulation in the U.S. — similarly used RCP8.5 in an attempt to discredit climate science. The DOE report “selectively focuses on high-end emissions scenarios, like RCP8.5, portraying them as failed predictions, to argue that the risks of climate change are exaggerated,” a comment submitted to the DOE on behalf of more than 85 scientists said. (The DOE report was written by five researchers who have long propagated contrarian views on climate change. In its final February rule rescinding the endangerment finding, the EPA stated that the agency is no longer relying on the DOE report “in light of concerns raised by some commenters.”)
“A tripling of global CO2 emissions by 2100,” as envisioned in RCP8.5, “may never have been particularly plausible even back in 2011 when RCP8.5 was originally published,” a trio of climate scientists wrote for the Climate Brink blog on May 18 on the retirement of the high-end scenario. “But a 21st century of increasing fossil fuel use leading to a doubling of emissions was within the realm of the possible.” It’s a “sign of progress” that the world is not heading toward a doubling of emissions, the researchers wrote, saying that the retirement of RCP8.5 doesn’t undermine “the edifice of all of climate science as both President Trump and some overly excited internet pundits claim.”
Major Impacts of Climate Change
Trump’s post also incorrectly suggested that climate change is not a serious problem.
“For far too long Climate Activism has been used by Dumocrats to scare Americans, push horrible Energy Polices, and fund BILLIONS into their bogus research programs,” he wrote. “Unlike the Dumocrats, who use Climate Alarmism nonsense to push their GREEN NEW SCAM, my Administration will always be based on TRUTH, SCIENCE, and FACT!”
Hayhoe said that Trump’s claims follow a familiar pattern of climate denial: claiming that climate change isn’t bad or its impacts aren’t serious. But the retirement of RCP8.5 does not change the fact that consequential global warming is occurring and will continue to occur.
Van Vuuren said that “by far the most important news” from the new climate scenarios publication is that the lowest plausible emissions scenario is now higher than before, hitting 1.7 degrees Celsius “or slightly higher” — the equivalent of more than 3 degrees Fahrenheit — before falling to around 1.5 C by 2100. This would mean the world would substantially overshoot the longstanding goal of limiting warming to no more than 1.5 C above pre-industrial levels. The scenario, notably, also relies on a high degree of carbon removal, which as a technology has yet to be deployed at large scale.
“The main message is that because emissions have been increasing instead of decreasing, we have increasingly lost our sight on the climate goals, which were formulated to prevent dangerous climate change,” he said.
Currently, the world is approximately following the medium scenario, van Vuuren said, which would lead to around 2.5 C to 3 C (4.5 F to 5.4 F), of warming by the end of the century. “That will bring quite substantial climate damage,” he said. “It will mean a substantial increase in extreme [weather and climate] events, it will mean sea level rise, it will mean impacts on agricultural yields, and also substantial increase in the risk of tipping points,” or levels of climate change that significantly and often irreversibly alter systems.
The RCP8.5 scenario translated to around 4.5 C of warming by 2100, or around 8 F. The new highest scenario includes expected warming of nearly 3.5 C, or around 6 F, and temperatures would continue to rise after 2100.
The Climate Brink post also explained that for a given level of warming, certain risks have increased. “So, even if the high-end emissions in RCP8.5 won’t materialize, the damages projected in these earlier climate simulations remain very much in play,” the researchers said.
Van Vuuren added that the temperature increases in the new paper are based on a “very simple” climate model but that further climate modeling will be done to understand how conditions will affect the climate system. In the past few years, he said that “we actually saw temperature increase going up much faster than in our scenarios.” The meaning of this is not yet known, but some research has suggested that this indicates the climate system is more sensitive to greenhouse gases, he said, which could mean much higher temperatures from those gases than previously thought. If that’s the case, “the temperature rise could still easily exceed 4°C,” or more than 7 F, the PBL post said.
The positive news, Hayhoe said, is that the scenarios show people can affect the trajectory of climate change. “The most important thing that these scenarios — both the older RCP ones and this newer set — show, without a shadow of a doubt, is that WE are the biggest uncertainty in terms of future impacts.”
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