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.

2. Undermining credibility.

Some will object to me pointing out that the IPCC has not predicted a global-scale societal catastrophe by 2030. They will inevitably suggest that whether or not the meme is strictly true, it is useful for motivating action on climate policy and therefore it is counterproductive to push back against it. I could not disagree more with this line of thinking.

The point of a document like the IPCC report should be to inform the public and policy makers in a dispassionate and objective way, not to make a case in order to inspire action. The fundamental reason for trusting science in general (and the IPCC in particular) is the notion that the enterprise will be objectively evaluating our best understanding of reality, not arguing for a predetermined outcome. I believe that the IPCC report has adhered to the best scientific standards but the meme of a predicted catastrophe makes it seem as though it has veered into full advocacy mode – making it appear untrustworthy.

An on-the-record prediction that may come back to haunt us

Apart from the inaccurate characterization that the IPCC has projected a catastrophe at 1.5°C, the other potentially harmful aspect of the media headlines above is that they put a timetable on the catastrophe that is very much in the near-term (2030). The year 2030 comes from the idea that we could first cross the 1.5°C threshold (at the annual mean level) in 2030, as is articulated in the report:

Now, if we immediately implement the global climate policies necessary to avoid 1.5°C of warming, then the prediction of a catastrophe will never be put to the test. However, as the IPCC report makes clear, achieving the cuts in emissions necessary to limit global warming to 1.5°C represents a truly massive effort:

Given that this effort would likely be massively expensive and represents a large technical challenge, it is unlikely to occur. This means that we are likely to pass 1.5°C of warming sometime in the 2030s, 2040s or 2050s. At this point – assuming that nothing resembling what most people would consider to be a global societal catastrophe has occurred – the catastrophe meme associated with the 2018 IPCC report will be dredged up and used as ammunition against the credibility of climate science and the IPCC. I fear that it will be used to undermine any further scientific evaluation of impacts from global warming.

In my experience, the primary reason that people skeptical of climate science come to their skepticism is that they believe climate scientists are acting as advocates rather than dispassionate evaluators of evidence. They believe climate scientists are acting as lawyers, making the case for climate action, rather than judges objectively weighing facts. The meme of a global catastrophe by 2030 seems to put a prediction on the record that is likely to be proven false and thus likely to reinforce this notion of ‘climate scientists as untrustworthy activists’ and thus harm the credibility of climate science thereafter.