Q&A

Global warming 'hiatus' never happened, say climate scientists

A new report says there's more evidence that global temperature data from a few years ago suggesting a pause in warming was wrong. Ocean temperatures have continued to rise.

New study says 2013 report suggesting pause in warming was incorrect

The IPCC proposed in 2013 that a pause in ocean warming had occurred, but scientists say that was an error in interpreting data. (Jonathan Hayward/Canadian Press)

Three years ago, the Intergovernmental Panel on Climate Change reported a 15-year-long plateau in ocean surface temperature changes. The report was controversial, sparking worries that it would fuel climate change skepticism and prompting other scientists to question the IPCC's results

Now, a new report says there's evidence that the data the IPCC was using in 2013 was incorrect and that the ocean has continued to grow warmer.  

When did the controversy begin?

Ocean surface temperatures are a good place to look for global trends because ocean temperatures don't change much daily, making it easier to measure long-term trends.

Over more than a decade, American scientists at the National Oceanic and Atmospheric Administration (NOAA) were collecting data on ocean surface temperatures that became part of the controversial IPCC report. 

But in 2015, the NOAA published an update that said the previous measurements suggesting a warming hiatus were wrong. The data now suggests there was never a warming hiatus and that the Earth has been warming faster than ever

The about-face sent climate change skeptics into a frenzy. The U.S. House of Representatives science and technology committee began an investigation and some accused the scientists of politicizing their data.

Since then, the data has been analyzed and re-analyzed, and yesterday's report confirms what most scientists have said: there was never a hiatus in the warming of ocean temperatures.

Why is it difficult to take the temperature of the ocean accurately?

You'd think it would be pretty easy — stick thermometer in, wait a bit, write it down. But the process is much more sophisticated than that.

For starters, there are a number of different types of instrumentation used to measure ocean surface temperatures: Argo floats (they almost look like free-floating rescue buoys), more permanent buoys, on-ship measurements and satellite measurements. Before the 1990s, most measurements were done by ships. Since then, buoys have been the primary source of temperature data. 

Because buoys sit directly in the water, the temperatures they record are often cooler than ship-based temperature measurements. (Argo.ucsd.edu)

According to Zeke Hausfather, one of the primary authors of the new report, the measurements from buoys are more accurate but often cooler than ship-based devices because they sit directly in the water. 

So when researchers switched to weighting their measurements more to buoy-based systems, it appeared as though the water wasn't warming, when it really was — to the tune of 0.12 C per decade.

Some scientists are now suggesting we should only look at measurements from one type of instrument at a time, reducing the potential for temperature biases in one direction or another. 

"Instead of trying to splice together ships and buoys and all these different measurements and having to figure out offsets and adjustments between them, let's just look at sea-surface temperature records created by one instrument," said Hausfather. 

The NOAA's initial assessment (blue) underestimated sea surface temperature changes. The red line shows the updated predictions after adjusting for a cold bias in buoy measurements. (Zeke Hausfather/UC Berkeley)

So, the ocean is actually warming after all? 

Yes. No matter how you look at it, ocean surface temperatures are warming rapidly and the trend is likely to continue. Though different models and measurement techniques might vary by small amounts — we're talking fractions of a degree — they all suggest that warming is happening.

No matter which model you choose or how you weigh each measurement, they all point to the fact that climate change is real and the ocean is warming at an alarming rate.

About the Author

Torah Kachur

Science Columnist

Torah Kachur is the syndicated science columnist for CBC Radio One. Torah received her PhD in molecular genetics from the University of Alberta and now teaches at the University of Alberta and MacEwan University. She's the co-creator of scienceinseconds.com.

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