No ‘pause’ in rising global temperatures: Study confirms NOAA estimates of ocean warming

New research has confirmed the results of a 2015 study led by scientists at the U.S. National Oceanic and Atmospheric Administration (NOAA) that showed there has been no “pause” in global warming.

The Intergovernmental Panel on Climate Change (IPCC) first noted in 2013 that, according to the data available at the time, the pace at which global temperatures were rising appeared to have slowed down starting around 1998. The “global warming pause” quickly became a favorite talking point of climate deniers and anyone else looking to forestall action on climate change, which they see as too costly.

Then, in a paper published in Science in June 2015, a group of scientists led by Thomas Karl, director of NOAA’s National Climatic Data Center in Asheville, North Carolina, detailed the results of their analysis that corrected for various sources of bias in the data on global surface temperatures, showing in the process that global warming had not gone on hiatus after all.

The NOAA study concluded that the problem was largely in how ocean surface temperatures were being calculated. Ocean temperatures had actually risen 0.12 degrees Celsius (about 0.22 degrees Fahrenheit) per decade over the past 19 years, the NOAA scientists determined, not 0.07°C (about .13°F), as had been previously estimated. “These results do not support the notion of a ‘slowdown’ in the increase of global surface temperature,” Karl and his co-authors wrote.

Climate deniers were not convinced, however. Among them was Republican Congressman Lamar Smith (R-TX), chair of the House of Representatives’ Committee on Science, Space, and Technology, who subpoenaed communications between the NOAA scientists in an attempt to prove that they had rushed their research into publication in order to bolster the Obama Administration’s climate policies.

But new research published yesterday in the journal Science Advances confirms NOAA’s findings about ocean warming over the past two decades.

Zeke Hausfather of the University of California, Berkeley led a team that evaluated the NOAA results published in 2015 and explored the reasons why the new NOAA records showed more warming over the past two decades than other measurements, such as those taken by the UK’s Hadley Centre.

There were two causes of the cool bias in previous estimates of ocean temperatures, Hausfather says: they failed to adjust for the transition in measurements from ships to buoys that has occurred in recent years, and they didn’t account for how a shift towards bigger ships and deeper hulls in the global shipping fleet over the last two decades impacted temperature measurements.

Both NOAA and Hadley are composite records, Hausfather explains: “They try to take data from lots of different types of instruments and combine them into a single long-term record. The challenge with this is that it creates uncertainties and judgement calls about how best to account for and correct changes in instruments (like the changing composition of the shipping fleet) or the change from one instrument to another (e.g. ships to buoy-based measurements).”

Hausfather and team took an entirely different approach to evaluating the data on ocean surface temperatures. “Luckily, over the past 15 years we have a wealth of new ocean measurement to work with to see which record is correct,” he said. “In our paper we create three separate ‘instrumentally homogenous’ temperature records (that is, records produced solely from one type of instrument) using floating buoys, satellite radiometers, and Argo floats. These instrumentally homogenous records don’t require any adjustments for changing measurement type, as they all use the same type of measurements.”

The researchers found that all three of the instrumentally homogenous records they compiled agreed with NOAA’s 2015 estimates of ocean warming, demonstrated a strong cool bias post-2003 in the old NOAA record, and showed a more modest though still significant cool bias in the Hadley record.

“Our results were nearly identical to those of NOAA despite using three independent datasets (buoys, satellite radiometers, and Argo floats), two of which (satellites and Argo) are not used at all by NOAA or other groups in their composite records,” Hausfather told Mongabay.

Here’s Hausfather explaining why past estimates underestimated ocean warming and how he was able to prove definitively that “NOAA scientists weren’t cooking the books”:

 

With Republicans like Rep. Lamar Smith now in control of both houses of the U.S. Congress and an incoming Republican president who has called global warming a hoax perpetrated by China and vowed to withdraw the US from the Paris Climate Agreement as soon as possible, there’s not likely to be a pause in attempts to defeat or delay American climate action any time soon.

But, given his independent confirmation of NOAA’s new estimates of ocean warming, Hausfather said that the idea that there was a pause in the rate at which global temperatures are rising is no longer defensible: “Regarding the apparent hiatus in warming, the combined impacts of fixing biases in the temperature record (as our paper discusses) and three record warm years (2014, 2015, and 2016) should firmly put to rest the idea that global warming has stopped.”

CITATION

• Karl, T. R., Arguez, A., Huang, B., Lawrimore, J. H., McMahon, J. R., Menne, M. J., … & Zhang, H. M. (2015). Possible artifacts of data biases in the recent global surface warming hiatus. Science, 348(6242), 1469-1472. doi:10.1126/science.aaa5632
• Hausfather, Z., Cowtan, K., Clarke, D.C., Jacobs, P., Richardson, M., & Rohde, R. (2017). Assessing recent warming using instrumentally homogeneous sea surface temperature records. Science Advances 3(1). doi:10.1126/sciadv.1601207