On Thursday, June 24, as the Northwest’s record-shattering heat wave approached, Cliff Mass posted a forecast he found hard to believe. By Monday, temperatures near the western Cascades foothills would exceed 108 degrees and they would reach 104 degrees and higher around Puget Sound.

“The event being predicted is so extreme and so beyond expectations that my natural inclination is to dismiss it,” Mass wrote. “But I can’t.”

His blog succinctly captured the historic event about to unfold in the kind of post that has helped make Mass, a professor at the University of Washington’s Department of Atmospheric Sciences, one of the region’s most influential meteorologists.

After the heat wave, he quickly assumed a far more controversial role as an outspoken critic of scientists who say climate change plays a big role in extreme weather events.

In a July 6 post, Mass declared that without global warming, we “still would have experienced the most severe heat wave of the past century.” In a follow-up post on July 13, he blasted as “profoundly flawed” a World Weather Attribution report by a team of 27 international scientists that concluded the heat wave would have been virtually impossible without human-caused climate change.

His blog posts serve as an online megaphone for Mass, who says it garners some 20,000 views on a typical day, and has received more than a half million views during some weather events.


His recent posts came at a time when Puget Sound governments and others in our region are scrambling to better prepare for such events. The heat wave contributed to the deaths of at least 125 people, according to preliminary state Department of Health data. And Mass has gotten strong pushback from scientists involved in the report as well as some other climatologists who say his ridicule increasingly makes him an outlier among scientists assessing the impacts of global warming.

The World Weather Attribution researchers, using statistical analysis, estimated the odds of this summer’s heat wave were one in 1,000 in today’s world but would have been at least 150 times more unlikely in preindustrial times. As early as the 2040s, their report said such events could occur, somewhere in the world, every five to 10 years.

In their models, the overall global impact of climate change resembles a kind of loading of the dice that can increase intensity of extreme-temperature events like the Northwest heat wave. In this case, they found climate change intensified the heat by about 4 degrees in the Seattle area to reach 108 degrees, significantly increasing the chances of death, according to a rebuttal document six of the researchers prepared in response to Mass.

Mass’s perspective differs.

He concluded climate change didn’t play a central role in an event largely caused by the natural variability of our regional weather. He notes the temperature soared by more than 40 degrees above the normal high, and climate change added only a few degrees, thus “a record-breaking unique heat wave” would have occurred even without global warming. In his blog, he lays out a golden rule that — based on this analysis — the bigger the temperature surge in an extreme event, the smaller the role of climate change, and accuses the World Weather Attribution report of “misinforming millions.”

Mass says his criticism is grounded in a deep knowledge of the intricate mix of ocean, mountains and atmospheric flows that help to produce Northwest weather, as well as climate models he runs.

Faron Anslow, a climatologist at the University of Victoria and co-author of the report, says he respects Mass’s forecasting abilities but not his climate analysis. He says Mass’s rejection of the report “clearly demonstrates how far out of his element Cliff is here.”


Nick Bond, state climatologist and a UW professor who co-teaches a course with Mass, said the report team used accepted statistical methods for looking at these types of events. “What they show makes sense to me — that the frequency and intensity of these events is increasing — even if I wouldn’t take as gospel the exact numbers,” Bond said.

Gavin Schmidt, senior climate adviser for NASA, in a series of tweets wrote “some folks keep getting the climate change connection wrong” and referred to Mass.

Schmidt dismissed Mass’s golden rule as “nonsense.”

“And it matters, because if you are someone who is going to make decisions about the future, you need to know this could happen again,” Schmidt, who was not part of the World Weather Attribution team, said in an interview.

A controversial figure

Mass says he does think climate change — caused by greenhouse gases from burning fossil fuel and other humans sources — is a problem. He is convinced this will result in more frequent heat waves and extremes later this century, and says “mankind should work to reduce emissions.” But he says his research leads him to conclude that in western Washington — due to a weakening of east winds that bring interior heat — these will be less intense than others forecast. And he doubts there will be a repeat of temperatures experienced in this summer’s heat wave in the next few decades.

“I don’t believe we are facing any kind of existential threat,” Mass said. “But it is not a good idea to muck around with the climate of the planet.”

Mass has sometimes gotten into very public disputes with other scientists, such as questioning the findings of a study about mountain snowpack decline in the West. He also has frequently derided the news media — including The Seattle Times — for headlines and reporting he believes overstate the threat of climate change.


Mass began his blog in 2008, with a large focus on problems in state math education, and since then often has ventured beyond meteorology.

In a March 13, 2020, blog post, he concluded the coronavirus situation “is far less apocalyptic than some are suggesting.” He noted U.S. COVID-19 deaths, at that time, tallied 36. He compared that to 61,000 flu deaths in 2017-18. “Coronavirus is not even in the same league as flu … we did not close down universities, businesses, and more for flu.”

The coronavirus death toll now exceeds 600,000 people.

Mass, in a recent interview, said “of course it (COVID-19) is worse than the flu,” but stands by his analysis as correct at the time.

Mass also has commented on the impacts of vandalism during protests. In August 2020, Mass, who is Jewish, wrote “Seattle has it(s) Kristallnacht and the photos of what occurred during the past weeks are eerily similar to those of 80 years ago.” Kristallnacht was a pogrom against German Jews and an attack on their property carried out by the Nazis in 1938.

That blog post got a strong backlash, including from his UW colleague, Daniel Bessner, an associate professor of American foreign policy, who told the university’s The Daily: “To compare the destruction of a Starbucks in 2020 to an act that foreshadowed a genocide, reflects not fully thought-out analogical reasoning.” Tacoma-based KNKX dropped a Mass radio segment due to what the station termed a “sensationalized and misleading” comparison.


Mass, who deleted the reference from his blog, later said he was referring not to protesters broadly but to those who destroyed property.

Mass said his views on the pandemic and the protests were not relevant to his views on climate science.

An isolated view

The World Weather Attribution report that drew fire from Mass resulted from an initiative launched in 2014 to try to provide real-time analysis of extreme heat and other events to assess the role of climate change.

The report said the Northwest heat wave could have been the equivalent of statistical bad luck aggravated by climate change, or there could have been something — beyond overall warming — that made such an event more likely. Their report states that possibility, while not indicated in the models, merits more investigation.

These quick turnaround documents are aimed at capturing media attention while the events are still fresh in peoples’ minds. Anslow notes most of these reports have later passed peer review and been published in scientific journals.

Mass has long been a critic of how climatologists portray the results of probability-based models that analyze climate change.


In 2017, for example, he used his blog to denounce efforts to link the powerful Hurricane Harvey, which unleashed record rainfall in Texas and caused $125 billion in damage, to climate change. His analysis found human-induced global warming played an “inconsequential role in this disaster.”

In the aftermath of the hurricane, a peer-reviewed study published in the Proceedings of the National Academy of Science found warming since the late 20th century resulted in a six-fold increase in the likelihood of such an event.

Mass said he stands by his analysis. “You would have had a devastating effect no matter what,” he said.

As he responds to the heat wave report, Mass has amped up these attacks. In emails to Anslow, he accuses the team of developing an “attribution science that makes virtually any extreme weather far more likely to occur under global warming.”

Mass says he’s working on a paper to document what he says are “the fundamental deficiencies” of this approach. He said it will be submitted for peer review and publication.

Anslow said he would welcome such scrutiny — so long as it’s peer reviewed.