The Intergovernmental Panel on Climate Change was in a bind.
The world’s premier scientific body on the climate had found, in a 2013 report, that it is extremely likely (95 percent confidence) that human activities are responsible for most of the observed warming of global temperatures since 1951. The panel was more certain than it had ever been in the past.
Yet the lay public did not seem to care. Polls have repeatedly shown that climate change is not a priority for most people.
So the IPCC scientists switched tacks. At a press conference on their report, they emphasized the record warmth the world had experienced in the past decade.
"More temperature records were broken than in any other previous decade," said Michel Jarraud, secretary-general of the World Meteorological Organization, of the 2000-10 stretch.
Rajedra Pachauri, the former head of the IPCC, and Thomas Stocker, co-chairman of Working Group I, echoed Jarraud’s message. It seemed a good way to make more immediate the abstract concept of climate change.
But by referring to a decadelong stretch of warming, the IPCC scientists may have unwittingly sowed the seeds of confusion, according to a study published yesterday in Nature Climate Change.
Rushing a slow-moving picture
Their words placed climate change within a chunk of time that people can more easily wrap their heads around. But they were also scientifically invalid. For a phenomenon to be remarkable in our planet’s climate, it has to last at least 30 years. Just one decade of warming does not cut it.
By referring to a decade of warming, the IPCC brought into play questionable claims made by climate deniers about a global warming "pause," the study finds.
The "pause" refers to the idea that rate of warming has slowed since 1998, compared to the 1990s. The pause does not actually exist, since observations over 15 years are not significant enough to be called a climate trend.
"Trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends," the IPCC stated in its 2013 report (ClimateWire, June 5).
Journalists present at the press conference lobbed questions about the pause at the scientists, said Warren Pearce, a sociologist at the University of Nottingham and a co-author of the study, in a statement.
The scientists immediately dismissed the pause. Stocker of Working Group I pointed out that "periods of less than around 30 years … are less relevant."
A confusing dialogue
The contradiction in the IPCC’s reliance, on one hand, on decadelong high temperatures and, on the other hand, its dismissal of the pause struck a confusing note, the study finds.
"The fact that scientists go on to dismiss the journalists’ concerns about the pause — when they themselves drew upon a similar short-term example — made their position inconsistent and led to confusion within the press conference," Pearce said in a statement.
One journalist at the conference asked Stocker, "you acknowledged that a 15-year period is less relevant from looking at a climate point of view and 30 years is what you would normally look at. If that’s the case, why did you even mention a 15-year period?"
The question went unanswered.
To avoid similar confusion in the future, scientists should strive to communicate certainty, but also be open to discussing details that they are less certain about, Pearce said in a statement.
"These need to be embraced and acknowledged in order to make climate change meaningful," he said.