The recent (July) release of the Department of Energy’s report, “A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate” has not been warmly received by many in the warming subculture. However, what surprised me about the study was the clear acknowledgment of climate change and humanity’s effect on it.
In his foreword, U.S. Energy Secretary Christopher Wright states that “Climate change is real, and it deserves attention.” Sure, he immediately follows that statement with “But it is not the greatest threat facing humanity. That distinction belongs to global energy poverty.” But simply acknowledging the scientific reality of climate change is a big deal. You might disagree with the last two sentences I quoted, but at least his framing acknowledges the science before making a policy statement.
He goes on to say, “Climate change is a challenge—not a catastrophe.” Challenge and catastrophe are normative words, as is “greatest threat,” clearly in the world of policy, not science. That’s not a criticism—that’s reality. It is also where, in my humble opinion as a scientist, the heated policy discussions should be: on the policy, not the science.
The authors of the report are a hodgepodge of climate curmudgeons and contrarians, but not (necessarily) outright climate denialists:
- John Christy is a climate scientist at the University of Alabama in Huntsville who has argued that the climate models run warm and described himself as “a strong critic of scientists who make catastrophic predictions of huge increases in global temperatures and tremendous rises in sea levels.
- Judith Curry is the former chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. She later became a climate doubter, suggesting that humans did not cause warming and that climate scientists are motivated by funding.
- Steven Koonin is a professor in the Department of Civil and Urban Engineering at NYU’s Tandon School of Engineering. He has questioned whether we understand the risks posed by climate change well enough to take action.
- Ross McKitrick is a professor of economics at the University of Guelph and a senior fellow of the Fraser Institute. His writings include climate denial, and he (initially?) disputed the hockey stick temperature plot.
- Roy Spencer is a principal research scientist at the University of Alabama in Huntsville and the U.S. Science Team leader for the Advanced Microwave Scanning Radiometer on NASA’s Aqua satellite. He believes that anthropogenic greenhouse gas emissions have caused some warming, but that cloud cover dominates warming.
Note that my summaries may not be indicative of these folks latest thinking on climate change—their views seem to change over time. While they are all Ph.D.s, they are not exactly a dispassionate group. And throwing an economist in there is like adding an extra devil on everyone’s shoulder (I’m being facetious here [I think…]).
Scientists with policy preferences make me nervous. And the stronger the policy preferences are, the nervous-er I get. Whether purposely or subconsciously, scientists that make strong policy statements may cherry-pick the science to support their policy positions. This happens on both sides of policy arguments. Scientists might argue that they keep their science separate from their policy preferences, but there is often intellectual diffusion between the two. Even if a scientist succeeds in keeping the two separate, there’s the perception that the scientist, and thus the science, is biased—a far stronger force than whatever the unprovable reality is. The Intergovernmental Panel on Climate Change is a victim of this, as well, where the scientific reports strive to focus on the science while the leaders write press releases dripping with policy preference.
So, what surprising stuff (from my perspective) did these authors conclude? They conclude that emissions are increasing the concentration of carbon dioxide in the atmosphere, noting that carbon dioxide is a greenhouse gas that exerts a warming influence on climate and weather. So, again, there’s an acknowledgment of the science.
They observe that, “There is evidence that scenarios widely used in the impacts literature have overstated observed and likely future emission trends.” They are referring to high-emission RCP8.5 and SSP5-8.5 scenarios, and they are correct. There is some debate in the literature (and acknowledged in the Intergovernmental Panel on Climate Change reports) about whether these scenarios should be included at all since we are currently heading down the SSP2-4.5 emissions scenario. One reason climate scientists run the 8.5 scenarios is that they include “all” the temperature scenarios in one run. Another reason is that it makes it easier to see the effects of warming on various environmental situations. However, assuming a well-behaved climate (a biggish assumption), we are nowhere near heading down that scenario.
While RCP8.5 and SSP5-8.5 are not worst-case scenarios, research suggests that the odds of us following this pathway are about 0.5 percent. The Intergovernmental Panel on Climate Change included SSP5-8.5 in their latest reports because, however unlikely, it was still possible. This seems reasonable to me. A 0.5 percent chance is a 1-in-200-year event, so it’s not a cray-cray possibility. After all, we (generally) design public infrastructure to survive the 500-year flood, and the biggest driver of future uncertainty is probably the human response to rising emissions. As we’ve seen lately, policies and actions on emissions can change abruptly.
In the book I am writing on warming and water, I have a section that attempts to address the question “Which Future is the Future?” or, more accurately, “which future should you use in planning for climate change?” This is a policy question informed by science, largely driven by risk tolerance. For example, South Africa plans for 50-year droughts while the United Kingdom asks its water providers to plan for 500-year drought events, and the State of Victoria requires water planning for 10,000-year events. In Texas, we plan for the worst backward-looking drought over the past 130 years (or less, depending on the record). Scientists should quantify this risk (to the extent possible) and leave risk tolerance decisions to policymakers.
The question of what to plan for is also something of an economic question that can inform policy. For example, an economic consideration might include balancing the costs of running out of water with those of ensuring water robustness. Economists have also attempted to identify the “optimal” amount of warming given the balancing between costs (impacts + mitigation) versus benefits. If only market damages are considered with moderate discounting, 2 to 3 °C (3.6 to 4.5 °F) of warming is the answer. If non-market damages are also included and future generations are more valued (low discounting), then 1.5 to 2.0 °C (2.7 to 3.6 °F) is optimal.
Another issue is managing risk in the face of uncertainty. Some of us (including these authors) argue that we should assume greater risk given the uncertainty in climate predictions. Others suggest we should be more risk-averse, given that we don’t know exactly what will happen as we warm. For example, when a group of friends approaches an unknown quarry with water in the bottom, there’s always one friend willing to jump in from the cliff regardless of the risk of injury or death, while others may not jump out of concern over how deep the water is or what might be in the water. Scientists have identified several “gray swans” (tipping points or cascading tipping points) and acknowledged that there are always unidentifiable “black swans.” Whether you jump or not depends on your perception and tolerance of that risk. This is a policy decision, not a scientific one (although, again, the science provides information to the policymakers [or the jumpers]).
As for the rest of the report, buyer beware. There’s a blur of spin and a table of pies from cherry-picking. One laugh-out-loud moment is when the authors argue that ocean acidification is not a big deal because “Most ocean life evolved when the oceans were mildly acidic,” while omitting that this was 3.8 to 3.2 billion years ago, when there was little oxygen in the atmosphere and lifeforms were bacterial. Regardless, it was nice to see some acknowledgment of the science when it appears. I wouldn’t have been surprised if it was not in there.