Temperature Trends

No Global Warming Hiatus After All Redux?

Sometimes climate science just doesn't seem all that "settled."


Andrew Parfenov/Dreamstime

A new study bolsters the controversial 2015 study by National Oceanic and Atmospheric Administration (NOAA) researchers that adjusted sea surface temperatures in an attempt to take account of measurement changes from ships to scientific buoys. After the adjustments were made to the record, the researchers reported:

Here we present an updated global surface temperature analysis that reveals that global trends are higher than reported by the IPCC, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a "slowdown" in the increase of global surface temperature.

The NOAA researchers concluded that the oceans are warming at 0.12 degrees Celsius (0.22 degrees Fahrenheit) per decade since 2000, which is nearly twice as fast as earlier estimates of 0.07 degrees Celsius per decade. This rate is similar the warming that occurred between 1970 and 1999.

As I noted at the time: "It could be that everyone else is wrong and the new study is right; but it could be also that it is an exercise in confirmation bias. Only time and more research will tell."

Interestingly, a February 2016 article by prominent proponents of man-made climate change in the journal Nature Climate Change essentially contradicted the NOAA study and reported:

It has been claimed that the early-2000s global warming slowdown or hiatus, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations. The evidence presented here contradicts these claims.

As I noted at the time, Nature News reported:

An apparent slowing in the rise of global temperatures at the beginning of the twenty-first century, which is not explained by climate models, was referred to as a "hiatus" or a "pause" when first observed several years ago. Climate-change sceptics have used this as evidence that global warming has stopped. But in June last year, a study in Science claimed that the hiatus was just an artefact which vanishes when biases in temperature data are corrected.

Now a prominent group of researchers is countering that claim, arguing in Nature Climate Change that even after correcting these biases the slowdown was real.

Now comes a new study in Science Advances by the independent group of researchers associated with Berkeley Earth which parses the sea surface data and finds that the adjustments made in the NOAA study are largely correct. The study notes that the modern buoys tend to have a cold bias compared to those made earlier by oceangoing ships. Once this bias is taken into account sea surface temperatures have been rising steadily which suggests that there has been no "hiatus" in global warming. The press release from the University of California, Berkeley notes:

The new study, which uses independent data from satellites and robotic floats as well as buoys, concludes that the NOAA results were correct. The paper will be published Jan. 4 in the online, open-access journal Science Advances.

"Our results mean that essentially NOAA got it right, that they were not cooking the books," said lead author Zeke Hausfather, a graduate student in UC Berkeley's Energy and Resources Group. …

Berkeley Earth

"Only a small fraction of the ocean measurement data is being used by climate monitoring groups, and they are trying to smush together data from different instruments, which leads to a lot of judgment calls about how you weight one versus the other, and how you adjust for the transition from one to another," Hausfather said. "So we said, 'What if we create a temperature record just from the buoys, or just from the satellites, or just from the Argo floats, so there is no mixing and matching of instruments?'"

In each case, using data from only one instrument type – either satellites, buoys or Argo floats – the results matched those of the NOAA group, supporting the case that the oceans warmed 0.12 degrees Celsius per decade over the past two decades, nearly twice the previous estimate. In other words, the upward trend seen in the last half of the 20th century continued through the first 15 years of the 21st: there was no hiatus.

"In the grand scheme of things, the main implication of our study is on the hiatus, which many people have focused on, claiming that global warming has slowed greatly or even stopped," Hausfather said. "Based on our analysis, a good portion of that apparent slowdown in warming was due to biases in the ship records."

Somehow the science does not seem all that "settled."