Global warming 'hiatus' never happened, say climate scientists

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. 

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. 

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.