2014, 2015, and 2016 each broke the global temperature record. A new study led by climate scientist Michael Mann just published in Geophysical Research Letters used climate model simulations to examine the odds that these records would have been set in a world with and without human-caused global warming. In model simulations without a human climate influence, the authors concluded:

There’s a one-in-a-million chance that 2014, 2015, and 2016 would each have been as hot as they were if only natural factors were at play.

There’s a one-in-10,000 chance that 2014, 2015, and 2016 would all have been record-breaking hot years.

There’s a less than 0.5% chance of three consecutive record-breaking years happening at any time since 2000.

There’s a 0.1%–0.2% chance of 2016 being the hottest on record.

To put those numbers in perspective, you have about a one-in-3,000 (0.03%) chance of being struck by lightning in your lifetime. You have about as much chance of being struck by lightning this year as 2014, 2015, and 2016 each being as hot as they were due solely to natural effects. That means denying human-caused global warming is like planning to be struck by lightning three years in a row. Perhaps a tinfoil hat will help.



On the other hand, in model simulations accounting for human-caused global warming, the odds of these events goes up substantially:

There’s a 1–3% chance that 2014, 2015, and 2016 would each have been record-breaking hot years.

There’s a 6–12% chance that 2014, 2015, and 2016 would be the three hottest years on record.

There’s a 30–50% chance of three consecutive record-breaking years happening at any time since 2000.

There’s a 20–27% chance of 2016 being the hottest on record.

It’s unusual to have three consecutive record-breaking years even with the aid of global warming, but without the human climate influence, it simply wouldn’t happen.

Denial from the Trump admin and UK allies

These findings tie in to the “leaked” the National Climate Assessment report, which climate scientists sent to the New York Times for fear that the Trump administration would censor or suppress the document. Previous drafts of the report were available to the public, although few take notice before the final version is published. Climate scientists worried that the administration would tamper with that final version. Among the report’s conclusions:

Many lines of evidence demonstrate that it is extremely likely [95%–100% confidence] that human influence has been the dominant cause of the observed warming since the mid-20th century … the likely range of the human contribution to the global mean temperature increase over the period 1951–2000 is … 92%–123%.

This conclusion is consistent with the latest IPCC report, which likewise concluded that humans are responsible for all of the global warming since 1951. These conclusions are denied by many members of the Trump administration. For example, Trump’s EPA administrator Scott Pruitt said earlier this year:

I would not agree that [CO2] is a primary contributor to the global warming that we see.

Similarly, when Trump’s Department of Energy secretary Rick Perry was confronted with the 100% human contribution to global warming since 1951, he responded by saying “I don’t believe that ... don’t buy it.”

Senator Al Franken and Energy Secretary Rick Perry in a US Senate energy budget hearing.

And of course the president himself has called global warming a Chinese hoax, and didn’t mention science once in his shameful speech declaring his intent to withdraw America from the Paris international climate agreement.



Across the pond, serial climate misinformer Nigel Lawson recently went on BBC Radio 4 and claimed that global temperatures have declined during the past 10 years. That, of course, is patently absurd considering the record-breaking temperatures we’ve experienced over the past 3+ years. In fact, the short-term warming trend over the past 10 years is higher than the long-term trend.



.@BBCr4today airs false statements on climate by Lord Lawson in the name of balance. Scientists fact-checkhttps://t.co/jIvKEuKxj5 pic.twitter.com/oowi8QnlfB — Climate Feedback (@ClimateFdbk) August 10, 2017

Scientists were rightly appalled that the BBC once again made the “ignorant and irresponsible” decision to host a climate science denier.



Censorship isn’t the problem – denial is

It’s understandable that climate scientists would worry about the possibility that the Trump administration would censor their findings. Not only has the administration denied this politically-inconvenient science, but the Republican Party has a history of censoring climate science research. That’s what the George W Bush administration did just a decade ago. And the Trump administration has been telling government scientists not to use the phrase “climate change” and deleting climate science information from government websites.

At the American Geophysical Union conference (the largest annual meeting of climate scientists) last December, climate scientists expressed fears about this type of censorship. Many took to the streets to stand up for science. The scientists pledged to have learned the lessons of the Bush administration censorship, and not to allow the Trump administration to do the same. That’s why the National Climate Assessment report was sent to the New York Times. This time, climate scientists are fighting back against censorship of their science.

Unfortunately, scientific censorship is no longer our main concern. It was an effective strategy over a decade ago, when most people remained blissfully unaware of the threats posed by human-caused global warming. But since then, the issue has become politicized. As Trump and Pruitt and Perry have illustrated, denying basic climate science has become the political norm among Republican Party leaders.

Simply put, it’s possible that the Trump administration would have censored or suppressed the National Climate Assessment report, but even an uncensored report doesn’t threaten them. The document mostly reiterates the findings of previous reports, like the last IPCC assessment. Political party leaders would just add it to the stack of documents and evidence whose inconvenient findings they deny.

That’s the problem we now face. It’s not one that physical scientists can solve – at least not without the aid of social science research. We’ve had enough evidence telling us about the need to act on climate change for decades. More evidence won’t convince people; we now have to figure out the best ways to communicate it, as climate scientists like Katharine Hayhoe are learning:



Global Weirding with Katharine Hayhoe.

In the meantime, we’re left wondering how many lightning strikes it will take to shock the climate science denial out of our system. We’ve been struck by three in a row, yet the denial is still going strong.

