The IPCC Report on the Impacts of Climate Change is Depressing

Last week, the United Nations Intergovernmental Panel on Climate Change (IPCC) released its synthesis on the state of scientific knowledge on climate change. Coverage has been widespread and predictably dramatic. The Washington Post says the World is on brink of catastrophic warming, The Guardian reports Scientists deliver ‘final warning’ on climate crisis: act now or it’s too late, and The New Yorker translates the report's findings into Wake up! This is your last chance, humanity.

I count myself among those depressed by the report, but not for the reasons you might think. As a climate scientist, with nine of my own research papers referenced in the IPCC report, I value sober, even-handed analysis above all else. What drew me to science and what gives science its authority in society is the notion that it at least strives to deliver objective analysis rather than goal-oriented advocacy.

Unfortunately, the portions of the IPCC report that deal with impacts and adaptation—the sections that inform the headlines above—do not adhere to this principle. Instead, they read less like a serious scientific assessment and more like a flier for an activist meeting, stringing together mashups of loosely related, but bad-sounding research “findings” in a sloppy and unprincipled way.

The goal of these portions of the report is clear: paint as bleak a picture as possible. That motivation pervades the entire impacts section, but the chapter on risks to agriculture serves as an illustrative example. In this chapter, one of the triumphs of the modern world—our dramatically increased agricultural productivity—is swept under the rug with contortions and obscurantism that can only be meant to heighten alarm about future food security.

Perhaps the most important fact for understanding climate change’s implications for food security is this: Since the 1960s, the world has warmed about 1°C and global yields (tonnes per acre) of all major crops have increased substantially. In the IPCC’s 194-page chapter on agriculture under climate change, this critical fact is mentioned in passing one time, and there is no figure like the one below illustrating it.

The historical increase in yields is not because climate change itself necessarily enhances yields, but because countervailing influences like the adoption of fertilization, mechanization, irrigation, selective breeding, pest control, and other factors have vastly outweighed any negative impact from climate change.

This historical fact is relevant for projections of the future because, over the next 60 years, we expect a similar rate of warming as we saw in the last 60 (even assuming the world does not meet the Paris Agreement goals of emissions reductions), and there is no reason to believe that these countervailing forces will suddenly stop. Every year, technology improves, and more farmers, not fewer, adopt modern practices.

Yet despite clear historical trends, the IPCC discusses decreases in crop yields ad nauseum throughout the chapter. Herein lies the obscurantism. Although most readers will understand the word “decrease” to mean a decrease relative to today, the IPCC uses the word to mean a decrease relative to a hypothetical world without climate change. So crop yields can be projected to continue to increase overall, but still be said to decrease compared to a hypothetical world with no climate change but in which everything else is the same.

In this way, the IPCC reports that historically, climate change has decreased yields for wheat by 4.9%, corn by 5.9%, and rice by 4.2%. But when you place these impacts in the context of massive background yield growth, the impact of climate change is seen to be quite small.

The IPCC’s appetite for bad news is even more apparent when its report discusses projections of crop yields going forward. The authors state that our ability to adapt is “insufficient to offset the negative impacts of climate change.” This statement seems to imply that the IPCC is projecting a net decrease in crop yields over the remainder of the century, but it turns out this is more language games and obscurantism.

The IPCC narrowly defines adaptation as only those actions explicitly taken to reduce the impact of climate change—if some technological or socioeconomic trend would have occurred regardless of climate change, then it doesn’t count as adaptation. For example, the adoption of tractors instead of manual labor can cause a large increase in yields, but this would not be an explicit adaptation to climate change, and thus it would not be considered in a projection of future yields that “accounts for adaptation.”

This definition allows the IPCC to imply that crop yields will decrease in the future in absolute terms relative to today, even while taking future adaptation into consideration. But this dire prediction would only come to pass if all technological and socioeconomic progress that has led to historical yield growth suddenly came to a halt. As we are possibly on the brink of a new revolution using gene editing technologies to create more resilient crops, such a future seems exceedingly unlikely. This is also far from what another United Nations entity, the Food and Agriculture Organization, projects. That organization includes technological advancement in its projections and foresees large future increases in all major crop yields despite assumed detrimental impacts from climate change.

In addition to dismissing countervailing factors responsible for yield growth, the IPCC also seems to be engaging in other cherry-picking intended to exaggerate the negative impact of climate change on food supply. For example, one major study the IPCC cites indicates that climate change itself enhances global wheat, rice, and soybean yields (while reducing maize yields). But is this result actually reported in the chapter? It is not. Instead, the IPCC chooses to report that the study “projected that climate change impacts on major crop yields appear sooner than previously anticipated” without mentioning that a substantial part of those climate change impacts are positive.

Also, when the chapter discusses weeds that might inhibit crop production, climate change, and enhanced CO2 are suddenly portrayed as being biologically beneficial rather than determinantal. Either this is because we are extremely unlucky, or this portrayal results from the predispositions of the researchers, which cause them to narrowly seek out ways in which climate change harms plants we like but helps plants we don’t like.

The report’s chapter on risks to agriculture is not an outlier. It is emblematic of the entire portion of the IPCC report that assesses the impacts of climate change and that drove the nearly hysterical media coverage. This and other IPCC reports are not objective assessments; they are, rather little more than assemblages of reasons to worry. If they weren’t, then you wouldn’t encounter findings like the “scenic beauty enjoyed by those who visit the vineyards in central Chile will decline by 18–28% by 2050.”

I desperately want the IPCC reports to serve as a means to cut through hyperbole and provide an anchor to which important decisions can be tethered. The realization that they cannot provide this service is a depressing one for a scientist in the field—and should be, as well, for readers who are otherwise misled into expecting catastrophe. Reform is needed to restore the credibility of the reports and climate science more generally. Only once these reports are able to be seen as objective analyses, will their recommendations warrant serious consideration by decision-makers and the public.

An earlier version of the chart in this post contained a mathematical error that has now been corrected.