Past research has claimed that the Earth went through a “global warming hiatus,” where for a period of time in the early 2000s, there was a slowdown in warming temperatures. By the end of 2017, over 200 published articles and studies revolved around this “pause.”
However, two new studies published in the journal Environmental Research Letters disprove all evidence of a pause in warming and show that temperatures have in fact been steadily on the rise.
“Many studies over the past decade have claimed to find a pause or slowdown in global warming and have typically posited this as evidence that is inconsistent with our understanding of global warming,” said James Risby, a lead author of one of the studies. “Global warming did not pause, but we need to understand how and why scientists came to believe it had, to avoid future episodes like this.”
Risby, part of the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO Australia), and a team of researchers reassessed the pause studies to help put the data and claims into a historical context.
The researchers made a note of how a “pause” had been identified and what methods were used in the studies while testing out different past and present datasets of global mean surface temperature (GMST).
“Our findings show there is little or no statistical evidence for a ‘pause’ in GMST rise,” said Risby. “Neither the current data nor the historical data support it. Moreover, updates to the GMST data through the period of ‘pause’ research have made this conclusion stronger. But, there was never enough evidence to reasonably draw any other conclusion.”
For the second study, a team of researchers reviewed climate models and observations to identify mismatches of global warming rates that would help explain why past studies came to the conclusions they did.
The researchers compared temperatures and projections of GMST of past climate models that were used in the pause studies and found that errors and misinterpretations of the predictions and data were made because of biases.
“We found the impression of a divergence – i.e. a divergence between the rate of actual global warming and the model projections – was caused by various biases in the model interpretation and in the observations. It was unsupported by robust statistics,” said Stephan Lewandowsky, the lead author of the second study and a professor from the University of Bristol.
Once the researchers accounted for these biases and reviewed the data again, there was no evidence of a pause to be found.
The two studies also provide some explanations for why so many past studies found evidence of a pause when in reality this was not the case, and the researchers note that perhaps data providers were not able to express the limitations of their data.
Another possible explanation could be that it takes time for researchers to correct a bias or inaccuracy in a study.
“A final point to consider is why scientists put such emphasis on the ‘pause’ when the evidence for it was so scant,” said Naomi Oreskes, a co-author of one of the studies from Harvard University. “An explanation lies in the constant public and political pressure from climate contrarians. This may have caused scientists to feel the need to explain what was occurring, which led them inadvertently to accept and reinforce the contrarian framework.”