Dissecting ‘Unsettled,’ a Skeptical Physicist’s Book About Climate Science

Five statements author Steven Koonin makes that do not comport with the evidence.

Melt water on the Greenland ice sheet. Credit: Education Images/Universal Images Group via Getty Images
Melt water on the Greenland ice sheet. Credit: Education Images/Universal Images Group via Getty Images

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Physicist Steven Koonin, a former BP chief scientist and Obama administration energy official,  seeks to downplay climate change risk in his new book, “Unsettled: What Climate Science Tells Us, What it Doesn’t and Why it Matters.”

His critics say he often draws general conclusions from specific slices of data or uncertainties (sometimes signaled by key words or phrases.) As a result, they say, his statements are frequently misleading, and often leave the reader with the incorrect impression climate scientists are hiding the truth. 

“Identifying, quantifying, and reducing uncertainties in models and observations is an integral part of climate science,” said atmospheric scientist Benjamin Santer of Lawrence Livermore National Laboratory. “The climate science community discusses uncertainties in an open and transparent way, and has done so for decades. It is simply untrue that Prof. Koonin is confronting climate scientists with unpleasant facts they have ignored or failed to understand.”


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Scientists who have been engaged in recent climate research also believe Koonin’s critique seems out of step with what has been happening in the field. He relies on the latest statements of the consensus science, but the most recent reports of the United Nations Intergovernmental Panel on Climate Change came out in 2013 and 2014. The IPCC’s updated assessment reports due out later this year and next year will almost certainly include recent studies that undercut Koonin’s conclusions.

Here are five statements Koonin makes in “Unsettled” that mainstream climate scientists say are misleading, incorrect or undercut by current research:

1. “The warmest temperatures in the US have not risen in the past fifty years.”

The average annual temperature in the contiguous U.S. has increased from 0.7 degrees to 1.0 degrees Celsius (1.2 to 1.8 degrees Fahrenheit) since the start of the 20th century. The year 2020 was the fifth-warmest year in the 126-year record for the contiguous U.S. And the five warmest years on record have occurred since 2012, NOAA reports.

There is a more marked increase in nighttime lows than in daytime highs (the “warmest” temperatures) because of factors like the cooling effect of daytime aerosol pollution and soil moisture evaporation. 

2. “Most types of extreme weather events don’t show any significant change—and some such events have actually become less common or severe—even as human influences on the climate grow.”

There have been statistically significant trends in the number of heavy precipitation events in some regions. Some regions have experienced more intense and longer droughts, while in other places, droughts have become less frequent, less intense, or shorter. Marine heatwaves, periods of extremely high ocean temperatures in specific regions, have become more than 20 times more frequent over the last 40 years due to human activity and the burning of greenhouse gases, according to a 2020 study that relied on satellite measurements of sea surface temperatures. 

3.  “Humans have had no detectable impact on hurricanes over the past century.”

In 2020, scientists detected a trend of increasing hurricane intensity since 1979 that is consistent with what models have projected would result from human-driven global warming. Rapid intensification of hurricanes has increased in the Atlantic basin since the 1980s, which federal researchers showed in 2019 is attributable to warming. A 2018 study showed that Hurricane Harvey, which hit Houston the prior year, could not have produced so much rain without human-induced climate change. That same year, a separate study showed that increased stalling of tropical cyclones is a global trend. 

4.  “Greenland’s ice sheet isn’t shrinking any more rapidly today than it was eighty years ago.”

Scientific findings indicate with high confidence that the Greenland ice sheet, the world’s second-largest land-based ice reservoir, has lost ice, contributing to sea level rise over the last two decades. And Greenland is on track to lose more ice this century than at any other time in the 12,000-year Holocene, the epoch encompassing human history, scientists reported in 2020.

The rate of ice melt in Greenland has varied widely over the decades, and there is evidence of a period of rapid melting in the 1930s that exceeded the rate of today. But the 1930s-era melt affected fewer glaciers, mostly those located entirely on land. Today’s melting involves more glaciers, most of them connected to the sea, with average ice loss more than double that of the earlier period. 

5. “The net economic impact of human-induced climate change will be minimal through at least the end of this century.

Global warming is very likely to have exacerbated global economic inequality, with the disparities between poor and wealthy countries 25 percent greater than in a world without warming, researchers concluded in 2019.

Only a limited number of studies have calculated the aggregate economic impact of climate change, not enough to place confidence in numeric results. But the data indicates with high confidence that climate change will aggravate other stressors, like inadequate housing, food or water supplies, with negative outcomes especially for the poor.