In late 2018 the Intergovernmental Panel on Climate Change (IPCC) released a report on the impacts associated with global warming of 1.5°C (2.7°F) above preindustrial levels (as of 2019 we are at about 1.0°C above pre-industrial levels) as well as the technical feasibility of limiting global warming to such a level. The media coverage of the report immediately produced a meme that continues to persist. The meme is some kind of variation of the following:
The IPCC concluded that we have until 2030 (or 12 years) to avoid catastrophic global warming
Below is a sampling of headlines from coverage that propagated this meme.
However, these headlines are essentially purveying a myth. I think it is necessary to push back against this meme for two main reasons:
1) It is false.
2) I believe that spreading this messaging will ultimately undermine the credibility of the IPCC and climate science more generally.
Taking these two points in turn:
1) The IPCC did not conclude that society has until 2030 to avoid catastrophic global warming.
First of all, the word “catastrophic” does not appear in the IPCC report. This is because the report was not tasked with defining a level of global warming which might be considered to be catastrophic (or any other alarming adjective). Rather, the report was tasked with evaluating the impacts of global warming of 1.5°C (2.7°F) above preindustrial levels, and comparing these to the impacts associated with 2.0°C (3.6°F) above preindustrial levels as well as evaluating the changes to global energy systems that would be necessary in order to limit global warming to 1.5°C.
In the report, the UN has taken the strategy of defining temperature targets and then evaluating the impacts at these targets rather than asking what temperature level might be considered to be catastrophic. This is presumably because the definition of a catastrophe will inevitably vary from country to country and person to person, and there is not robust evidence that there is some kind of universal temperature threshold where a wide range of impacts suddenly become greatly magnified. Instead, impacts seem to be on a continuum where they simply get worse with more warming.
So what did the IPCC conclude regarding the impacts of global warming of 1.5°C? The full IPCC report constituted an exhaustive literature review but the main conclusions were boiled down in the relatively concise summary for policymakers. There were six high-level impact-related conclusions:
So to summarize the summary, the IPCC’s literature review found that impacts of global warming at 2.0°C are worse than at 1.5°C.
The differences in tone between the conclusions of the actual report and the media headlines highlighted above are rather remarkable. But can some of these impacts be considered to be catastrophic even if the IPCC doesn’t use alarming language? Again, this would depend entirely on the definition of the word catastrophic.
If one defines catastrophic as a substantial decline in the extent of artic sea ice, then global warming was already catastrophic a couple decades ago. If global warming intensified a wild fire to the extent that it engulfed your home (whereas it would not have without global warming) then global warming has already been catastrophic for you.
However, I do not believe that changes in arctic sea ice extent and marginal changes in damages from forest fires (or droughts, floods etc.) are what most people envision when they think of the word catastrophic in this context. I believe that the imagery evoked in most peoples’ minds is much more at the scale of a global apocalyptic event. This idea is exemplified in Michael Barbaro’s question about the IPCC report that he asked on The New York Times’ The Daily:
“If we overshoot, if we blow past 1.5°C and 2°C degree warming, is it possible at that point that we’ve lost so much infrastructure, so much of the personnel and the resources required to fix this that it can’t be done anymore? Will there be enough of the world left to implement this in a way that could be effective?”
-Michael Barbaro, New York Times, The Daily, 10/19/2018
It is also articulated in a tweet from prominent climate science communicator Eric Holthaus:
If catastrophe is defined as global-scale devastation to human society then I do not see how it could be possible to read the IPCC report and interpret it as predicting catastrophe at 1.5°C or 2°C of warming. It simply makes no projections approaching such a level of alarm.