Climate scientists rebuff skeptics' arguments against 2014 'warmest year' claim

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Image: NASA

By Andrew Freedman2015-01-20 19:40:43 UTC

On January 16, two U.S. climate observing agencies jointly announced that 2014 was most likely the warmest year on record worldwide, beating previous record years such as 1998, 2005 and 2010. The announcement signaled the death knell of the argument that global warming "stopped" in 1998, which has been a popular rallying cry for climate change contrarians, from blog posts to speeches on the Senate floor.

With such high stakes, climate skeptics have been vigorously pushing back against the data, saying that the National Oceanic and Atmospheric Administration (NOAA) and NASA downplayed the uncertainties in their records and misled the public.

Temperature departures from average since 1880, according to NOAA data.

Image: Bob Al-Greene/Mashable

Headlines like "2014: The Most Dishonest Year on Record" have been posted on climate skeptic blogs, such as Watts Up With That, and a commentator for the popular British newspaper The Daily Mail all but accused NASA of lying to the press and the public about global temperatures, despite the open discussion of uncertainties both in NASA's press materials and during a press conference with audio that is publicly accessible.

The skeptics have focused mainly on one table in the temperature report issued on Friday, which explains the uncertainties involved in declaring 2014 the warmest year. The table would appear to indicate that 2014 only has a 38% chance of being the warmest year in NASA's data set, which isn't that convincing at first glance, and a 48% likelihood according to NOAA's data. (Each agency uses slightly different methods of calculating global average surface temperatures.)

Here is how the Daily Mail discussed the temperature record in a story published on Sunday. "The Nasa climate scientists who claimed 2014 set a new record for global warmth last night admitted they were only 38% sure this was true." The story portrayed NASA as backing off their claim that 2014 was clearly the warmest year on record according to its data set.

But NASA did no such thing.

NASA and NOAA scientists say they have not changed their tune about 2014, since the data clearly shows that it was most likely the warmest year to date since instrument records began in 1880. Furthermore, they argue that climate skeptics are twisting the meaning of uncertainty ranges and making it seem like there is far less confidence in temperature data than there actually is.

Climate science debates occur every day in the blogosphere and on cable news shows, but this particular fight about a major temperature record (and therefore, major news story) highlights the extent to which many boil down to mere contradiction and rejections of facts, rather than arguments based on competing lines of evidence.

Slide from a publicly available presentation showing the probabilities that 2014 was the warmest year on record.

Mashable reached out to Gavin Schmidt, the director of NASA's Goddard Institute of Space Studies (GISS), who helped make Friday's announcement and has been a target of the vigorous pushback from the climate skeptic community. Schmidt is mentioned several times in the Daily Mail story.

Schmidt told Mashable that NASA is not backtracking from its conclusion that 2014 was the warmest year in its records, and that climate skeptics — (some prefer to call them "climate deniers") — misunderstand the characterization of uncertainty that NASA provided on Friday.

Schmidt says there is, of course, some uncertainty in the global temperature data, which NASA has long acknowledged. But even when these uncertainties are considered, the data still shows that 2014 was most likely the warmest year.

"No-one disputes that there are uncertainties in estimating the global mean temperature anomaly — issues of spatial coverage, measurement practice changes over time, movement of stations etc. and we estimate that any one year's value comes with an uncertainty of about plus or minus 0.05 degrees Celsius, or 0.09 degrees Fahrenheit," Schmidt said in an email.

"2014 *is* the warmest year in the GISTEMP, NOAA and Berkeley Earth analyses," he said, referring to different data sets kept by different groups of scientists, including the one kept by his center and known as "GISTEMP."

Schmidt said there is considerably more confidence — albeit not complete certainty — that 2014 is the warmest year compared to 2010, which was the previous record-holder in GISTEMP.

Schmidt continued:

It is *likely* to have been the warmest year for the planet. Exact estimates of that likelihood are difficult to calculate (though a simple calculation we did - assuming that errors are uncorrelated from one year to another - does suggest ~38%, [which is] some one and a half times more than 2010," he said. "With the same assumptions, the chances that 2014 was warmer than 2010 is about 60%.

Schmidt said the uncertainties were "plainly and clearly discussed at the NASA/NOAA press conference on Friday." He referred to a slide in the presentation provided to reporters and the public, as well as the audio from a press conference, where the odds of 2014 being the warmest year are discussed around minute 13:47.

Deke Arndt, the head of the climate monitoring branch of the National Climatic Data Center in Asheville, North Carolina, told Mashable that his agency's characterization of uncertainty estimates were also being misconstrued by numerous bloggers and journalists.

Arndt says many journalists and skeptic bloggers in particular are making a basic mistake in interpreting what a range of uncertainty means.

"The entire community of journalists, well-meaning colleagues, bloggers would do well to remember that a "range of uncertainty" has a shape of its own," Arndt said.

An uncertainty range "does ***NOT*** mean" that each temperature within the given range is "equally likely," Arndt says.

"It resoundingly and definitively means something fundamentally different. Gavin's slide from the presentation shows this pretty beautifully," he said.

Given the intensity of the discourse on global warming, including relatively routine annual climate announcements, it's unlikely that most skeptics will be convinced that 2014 was the warmest year. At the end of the day, the discussion about a single calendar year obscures the more important long-term trend of warming air temperatures, warming and acidifying oceans along with melting ice sheets, all of which are hallmarks of manmade global warming. Including 2014, 14 of the top 15 warmest years have all occurred since 2000.