Something curious is going on in the world of climate advocacy. As THB readers know, projected future carbon-dioxide emissions from fossil-fuel combustion have been consistently revised downward in recent years, resulting in less projected warming. Yet rather than acknowledge this encouraging development, climate campaigners have shifted the goalposts by lowering the threshold of what they promote as apocalyptic.
Once projected 4C, 5C, or even 6C global average temperature increases to 2100 were justifications for demands that the world undergo a rapid transition to much lower trajectories. With such large changes in temperature looking increasingly unlikely with every passing year, climate campaigners have simply changed the demarcation of catastrophe from large to smaller projected changes in temperature — while maintaining exactly the same apocalyptic rhetoric.
In 2013, Robert Watson, former head of the Intergovernmental Panel on Climate Change (IPCC), warned ominously that the world was headed toward a very large increase in global temperatures over pre-industrial (1850-1900) values:
We now know we can’t rule out a possible 5°C temperature rise, and we need to start preparing for it.1
Five years later, in 2018, the Fourth U.S. National Climate Assessment (NCA4) shared a similar warning, concluding that the world was following the trajectory of a scenario called RCP8.5, with a median projected warming in 2100 of ~4.3C, ranging up to ~5.7C:
Which scenario is more likely? The observed acceleration in carbon emissions over the past 15–20 years has been consistent with the higher future scenarios (such as RCP8.5) considered in this assessment. Since 2014, however, the growth in emission rates of carbon dioxide has begun to slow as economic growth has become less carbon-intensive with the trend in 2016 estimated at near zero. Preliminary data for 2017, however, indicate growth in carbon emissions once again.
Throughout its assessment, the NCA4 contrasted the “higher emissions” RCP8.5 with the “lower emissions” scenario, RCP4.5, which projects ~2.8C warming to 2100.
The NCA4 presented the ~4.3C scenario as a baseline — where we were headed — and the ~2.8C scenario as the consequence of successful “mitigation,” with the differences between the two indicating large benefits of successfully getting onto that RCP4.5 path.
You can see how the NCA4 summarized the differences in the figure below.
The NCA4 explained the positive outcomes associated with getting onto a ~2.8C trajectory:
Many climate change impacts in the United States can be substantially reduced over the course of the 21st century through global-scale reductions in GHG emissions (Figure 29.2). While the difference in climate impact outcomes between different scenarios is more modest through the first half of the century, the effect of mitigation in avoiding climate change impacts typically becomes clear by 2050 and increases substantially in magnitude thereafter.
The NCA4 argued that getting onto a <~3C trajectory would reduce the magnitude of and uncertainty in future impacts of climate change, and illustrated that claim with the figure below — which shows that <~3C warming by the end of the century would result in a small, ~1% effect on U.S. GDP by the end of the century, around one tenth of the consequences of the maximum value of the >4C projection.
Compared to RCP8.5, lower temperatures due to mitigation under either of the lower scenarios (RCP2.6 or RCP4.5) substantially reduce median damages (dots) to the U.S. economy while also narrowing the uncertainty in potential adverse impacts.
Throughout the administration of President Joe Biden, RCP8.5 (~4.3C) was presented as the current trajectory and RCP4.5 (~2.7C) was framed as policy success, even if not achieving the goals of the Paris Agreement. The Biden Administration’s framing had a solid scientific basis: From 2010 to 2021 Google Scholar reports ~17,000 peer-reviewed paper that contrasted RCP8.5 with RCP4.5 — baseline versus mitigation.
Flash forward just seven years to 2025 — cue the record scratch.
Today, the world is tracking below a RCP4.5 emissions trajectory and a strong consensus has developed that the world is headed to <3C warming by 2100, with many projections at <2.5C.2 That does not mean that climate change is not a problem or that continued efforts on mitigation and adaptation do not make sense. But it does mean that climate change is not the same issue as it was a generation ago.
That the issue has evolved in profound ways is now accepted.
For instance, the U.K. energy and climate secretary, Ed Miliband, argued in the Financial Times last week:
[W]e have gone from a world heading to 4C or more of global warming to one of around 2.3-2.5C.
Similarly, the United Nations reported last week its analysis that indicated that projected 2100 temperatures had dropped substantially from their 2024 analysis:
Implementing only current policies would lead to up to 2.8°C of warming, compared to 3.1°C last year.
You might think that going from an expected future of >4C and even >5C (and some brought >6C into play) to revised expectations of <3C — consistent with what the U.S. NCA claimed would be policy success just 7 years ago — would be received as good news.
Far from it.
Instead, the threshold of the apocalypse has been defined way down. Here are some examples:
United Nations: “The world was headed for a “climate breakdown” at a global average temperature rise of 2.8C under existing government policies, according to the latest UN report ahead of global climate talks.” (Source: FT)
The Guardian: “The world is on track for 2.5C-2.9C of global heating, which would almost certainly be beyond tipping points for the collapse of the Greenland and west Antarctic ice sheets.”
Daniel Swain: “A 2.5 to 3 degree warmer world is a catastrophe not just for people who live in the global south, not just for poor nations, but also for wealthy nations. It’s a catastrophe for all global ecosystems, for anybody who cares about anything that relates to the natural world anywhere, but also people.”
Johan Rockström: “The world is heading towards 2-3C of global warming. This sets Earth on course to cross multiple dangerous tipping points that will be disastrous for people across the world. To maintain liveable conditions on Earth and enable stable societies, we must do everything possible to prevent crossing tipping points.”
We can see where this strategy is headed: Eventually, the claim will be that we are already in a world that has undergone catastrophic climate change — Just look out the window! We see this in the incessant efforts to link every extreme weather event to climate change (bear attacks in Japan as well).
While the propaganda value of overheated claims can be debated, the moving of the apocalypse goalposts runs into scientific realities, such as:
The IPCC has not come remotely close to identifying a threshold of doom, much less equating <3C outcomes projected in 2025 with >4C outcomes projected a generation ago;
Some advocates use a slogan — “every tenth of a degree matters.” However, there is no research (that I am aware of) that purports to quantify climate impacts as a function of tenths of a degree of global average temperatures;
As the world warms, and the promised apocalypse does not materialize, the entire movement risks its credibility, as indicators of well being continue to move in positive directions. As the world sits on the brink of 1.5C today, arguably it already has.
As climate projections catch up to contemporary demography — and specifically continued lowering of projections of future population — there is good reason to expect that global temperature projections will continue to be revised downward in coming years.
The dynamic of of moving goalposts when prophesy fails is hardly new. Various millenarians famously moved the date of the rapture when the promised date came and went. Climate advocates do efforts to accelerate decarbonization of the economy no favors by denying that expectations of future changes in climate have evolved in a positive direction.
