What do the research literature and government reports actually say about human-induced climate change and its consequences?
Editor’s Note: The following are extracts from Unsettled: What Climate Science Tells Us, What It Doesn’t, and Why It Matters, by Steven E. Koonin.
The first two, which are brief, are from the introduction. One sets out the basic thesis of the book, and the other is a summary of Koonin’s background. The third, which is lengthier and lightly edited, comes from a chapter entitled “Apocalypses That Ain’t,” wherein Koonin discusses climate change’s effect on the economy.
From the Introduction
‘The Science.” We’re all supposed to know what “The Science” says. “The Science,” we’re told, is settled. How many times have you heard it?
Humans have already broken the earth’s climate. Temperatures are rising, sea level is surging, ice is disappearing, and heat waves, storms, droughts, floods, and wildfires are an ever-worsening scourge on the world. Greenhouse-gas emissions are causing all of this. And unless they’re eliminated promptly by radical changes to society and its energy systems, “The Science” says earth is doomed.
Well . . . not quite. Yes, it’s true that the globe is warming, and that humans are exerting a warming influence upon it. But beyond that — to paraphrase the classic movie The Princess Bride: “I do not think ‘The Science’ says what you think it says.”
For example, both the research literature and government reports that summarize and assess the state of climate science say clearly that heat waves in the U.S. are now no more common than they were in 1900, and that the warmest temperatures in the U.S. have not risen in the past 50 years. When I tell people this, most are incredulous. Some gasp. And some get downright hostile.
But these are almost certainly not the only climate facts you haven’t heard. Here are three more that might surprise you, drawn directly from recent published research or the latest assessments of climate science published by the U.S. government and the U.N.:
- Humans have had no detectable impact on hurricanes over the past century.
- Greenland’s ice sheet isn’t shrinking any more rapidly today than it was 80 years ago.
- The net economic impact of human-induced climate change will be minimal through at least the end of this century.
So what gives . . .?
* * *
I’m a scientist — I work to understand the world through measurements and observations, and then to communicate clearly both the excitement and the implications of that understanding. Early in my career, I had great fun doing this for esoteric phenomena in the realm of atoms and nuclei using high-performance computer modeling (which is also an important tool for much of climate science). But beginning in 2004, I spent about a decade turning those same methods to the subject of climate and its implications for energy technologies. I did this first as chief scientist for the oil company BP, where I focused on advancing renewable energy, and then as undersecretary for science in the Obama administration’s Department of Energy, where I helped guide the government’s investments in energy technologies and climate science. I found great satisfaction in these roles, helping to define and catalyze actions that would reduce carbon-dioxide emissions, the agreed-upon imperative that would “save the planet.”
But then the doubts began . . .
From Chapter Nine: ‘Apocalypses That Ain’t’
In 2018, on the day after Thanksgiving (Black Friday), the second volume of the Fourth National Climate Assessment (NCA2018) was released. It deals with the projected impacts of human-induced climate change, and it immediately generated the now familiar headlines warning of impending economic disaster, among them:
- “Climate change will wallop the US economy” (NBC News)
- “Climate report warns of grim economic consequences” (Fox News)
- “Climate change could cost US billions” (Financial Times)
- “US climate report warns of damaged environment and shrinking economy” (New York Times)
Indeed, Key Message No. 2 of the report’s Chapter 29 reads:
In the absence of more significant global mitigation efforts, climate change is projected to impose substantial damages on the US economy, human health, and the environment. Under scenarios with high emissions and limited or no adaptation, annual losses in some sectors are estimated to grow to hundreds of billions of dollars by the end of the century.
Both the key message and the heated headlines greatly dismayed me — they’re clearly intended to be frightening. Yet I had studied the issue and knew that the projected net economic impacts were minimal. Let me explain.
I first looked into the economic impacts of climate change the year before, in 2017, when one of the world’s largest investment organizations requested my advice on climate science. Since they’d asked that I cover economic impacts, I had carefully read what the U.N.’s Fifth Assessment Report (AR5) had to say on the matter.
Projections of the economic impacts of a changing climate are highly uncertain. Of course, we already know there are great uncertainties in how the climate will change because of inadequate climate models and uncertainty in future emissions. And climate uncertainties are larger at the regional level than they are at the global level. For example, for the first five or six years of the recent California drought, many climate scientists said that human influences on the climate increased the risk of drought. Yet it took only about a year after the drought broke dramatically in 2016 for papers to appear claiming that a warming world would also mean a wetter California. Perhaps this is just the process of scientific understanding being refined. Less charitably, I get the distinct sense that the science is unsettled enough that any unusual weather can be “attributed” to human influences.
In addition, climate is only one of many factors influencing economic development and well-being. Economic policies, trade, technology, and governance are also important, and these are different in different countries and can change in unpredictable ways. Economic measures are highly regional, and their future uncertainties are compounded by the uncertainty of regional climate predictions. It is particularly difficult to predict how, and how much, a rising temperature would damage a society economically in the face of so many unknowns — among them the role that might be played by adaptation measures such as the raising of sea walls or shifts in what crops are cultivated that minimize, or sometimes even exploit, the impact of climate changes.
Despite those challenges, the AR5’s Working Group II — whose part of the assessment is devoted to the ecological and societal impacts of the changes in climate outlined by Working Group I — does say something about how world economic activity would be affected by a warming globe. Figure 9.4, a chart included in Unsettled, plots some 20 published estimates showing that the (by now familiar) projected global temperature rise of up to 3 °C by 2100 would negatively impact the global economy by — wait for it — 3 percent or less.
For my talk to the investors, I provided some important context that was missing from the U.N. report. An impact of 3 percent in 2100 — some 80 years from now — translates to a decrease in the annual growth rate by an average of 3 percent divided by 80, or about 0.04 percent per year. The IPCC scenarios (discussed in Chapter 3) assume an average global annual growth rate of about 2 percent through 2100; the climate impact would then be a 0.04 percent decrease in that 2 percent growth rate, for a resulting growth rate of 1.96 percent. In other words, the U.N. report says that the economic impact of human-induced climate change is negligible, at most a bump in the road. In fact, the first point in the executive summary to its Chapter 10 is:
For most economic sectors, the impact of climate change will be small relative to the impacts of other drivers (medium evidence, high agreement). Changes in population, age, income, technology, relative prices, lifestyle, regulation, governance, and many other aspects of socioeconomic development will have an impact on the supply and demand of economic goods and services that is large relative to the impact of climate change.
A 2018 article written by one of the IPCC’s coordinating lead authors reviewed a further four years of published papers and came to a similar conclusion:
The total economic impacts of climate change are negative, but modest on average, and . . . the severe impacts on less developed countries are caused primarily by poverty.
The consensus on the minimal overall economic impact of rising temperatures is well known to experts, though it’s an inconvenient one for those wishing to sound the alarm on climate. I was dumbfounded when I asked a prominent environmental policy-maker about the U.N. assessment and the response was: “Yes, it’s unfortunate that the impact numbers are so small.
At any rate, this background left me primed to weigh in on the breathless coverage that accompanied the release of Volume II of NCA2018. The last figure in that report’s final chapter is based on a 2017 paper published in Science magazine. It shows that projected direct damages to the U.S. economy at the end of the century grow with increasing global average temperature (shown as the anomaly relative to the 1980–2010 average). As in the IPCC projection for the world economy, the impacts on the U.S. are small: A very large warming of 5 °C (9 °F) at the end of the century would diminish the U.S. economy by 4 percent. (It’s worth noting that this 5 °C warming is relative to today’s temperatures, which are up 1 °C from pre-industrial values, making this equal to 6 °C of warming by the Paris Agreement accounting, which has set 1.5 °C as a goal.)
Like the U.N. report, NCA2018 fails to put this in context, but I can do so quite simply: The U.S. economy has grown at an average annual rate of 3.2 percent since 1930 (it’s almost 20 times larger now that it was 90 years ago). Under the conservative assumption that annual economic growth will average 2 percent for the next 70 years, the U.S. economy will be four times larger in 2090 than it is today. The purported climate impact of 4 percent in 2090 then corresponds to two years of growth. In other words, an additional warming of 5 °C (9 °F) by 2090 would delay the growth of the U.S. economy to that time — 70 years from now — by only two years. . . .
Within a few hours of the NCA2018’s release on Black Friday, I had drafted a short op-ed saying more or less what I have said here, which the Wall Street Journal published online on Monday. The next day, a prominent U.S. energy economist sent an email thanking me for making the point — alas, that person could never express that thanks publicly. The next week, one of the authors of the original 2017 research paper from which the estimates used in the assessment report were drawn expressed dismay at the way their results had been portrayed in the media.
The climate-science establishment, most notably the authors of NCA2018, reacted to my op-ed with silence. They did nothing to address the media’s catastrophizing. Perhaps they were embarrassed by their own doom-mongering. Or perhaps, like the policy-maker I mentioned earlier who wished the impact numbers had been greater, it was precisely the coverage they’d been hoping for.
As you’ve no doubt noticed yourself, the notion of climate-related economic disaster remains alive and well in the media and political dialogue. Economics has been called the “dismal science,” and I once joked to a prominent economist that the compounding of climate and economic projections is a “doubly dismal” enterprise. It is reasonable to expect that factors related to climate change — including shifts in agricultural conditions or variations in storm patterns — will have different economic impacts (and benefits) on certain populations and economic sectors. Yet contrary to popular belief, even the official assessment reports indicate that significant human-induced climate change would have negligible net economic impact on either the world or the U.S. economies by the end of this century.