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Katharine Hayhoe @KHayhoe
, 23 tweets, 8 min read Read on Twitter
The Fourth US National Climate Assessment was released on Friday. Since then, a number of politicians + pundits have made statements about it that are not accurate. As an author, I'm here to set the record straight. Here we go! (thread)
... when your phone goes dead right at the first tweet ...
First, a WH spokesperson said the report was based on the “most extreme” scenario. No: the report considered a very broad range of scenarios, from one where carbon emissions go negative to one where they continue to grow. Source:
Moreover, the scenarios chapter in Vol 1 discussed the scenarios in detail, and it concludes that “the observed increase in global carbon emissions over the past 15–20 years has been consistent with higher scenarios (very high confidence).” source:
Throughout the regional and sectoral chapter, the report makes every effort to discuss possible outcomes of multiple scenarios. On the risks to coastal infrastructure, for example, the Southeast chapter says this:
The WH spokesperson also said that future reports would be “transparent” - but this report was publicly reviewed. Authors were required to respond to each comment individually, and both the commments + our responses are available for anyone to read. Plus ...
Each key message is fully documented by a “traceable account” that contains full citations, sources, references, and documentation supporting that key message. In many cases, the traceable account section is as long as the chapter itself (!) How much more transparent can you get?
Then, Santorum claimed us authors were “driven by money”. After I picked myself up off the floor laughing, since we received $0 for writing the report, I invited him to watch this entertaining Global Weirding episode. I don’t think he did; but you should!
Next, Delay claimed that the report was “nothing more than a rehash of age-old 10- to 20-year assumptions made by scientists that get paid to further the politics of global warming.” In fact, the report includes the latest literature right up to the cut-off date, ...
...including the latest attribution studies for Harvey that quantify how human influence made the storm ~3x more likely and increased its rainfall “by at least 15% with a best estimate of 38%”. That’s pretty recent! Read more:
Finally, the president then said that he “didn’t believe” the report. But climate science isn’t a religion: it’s real, whether we believe in it or not. If our decisions are not based in reality, we are the ones who will suffer the consequences.
When it comes to a changing climate, the bottom line is this:

It’s real.

It’s us.

Scientists agree.

The impacts are already here and now.

But by acting now we can still avoid the most serious and even dangerous impacts.

Our future is in our hands.
If you’re wondering, I’m just one person, what can I do about it? Start here:
If you’re asking, isn’t it too late to fix this thing? Watch this:
And if you, like the president of the United States, are tempted to say, “it’s cold outside, so much for global warming!”, here is an episode just for you:
Do we think another 2000 page climate change report will change peoples’ minds if they’re already decided to reject the science because they believe climate solutions are incompatible with their political ideology? No. Watch:
But the national climate assessment does address the most pernicious myth that the greatest number of people have bought into; the myth that “it doesn’t matter to me” - when in fact, after the polar bear, we’re next. Read:…
Sarah Saunders says, “this report is based on the most extreme model scenario, which contradicts long-established trends.” That’s two false statements because: 1, we considered many scenarios including vv low ones; and 2, the chapter I wrote concludes this, based on actual data:
She then says, “modeling the climate is an extremely complicated science that is never exact.” That is absolutely true. And that’s why, in the chapter I wrote with @bobkopp called “Potential Surprises”, this conclusion is so worrisome. Source:
Over the last century, tho, it’s important to recognize that climate models - even the super-basic ones from decades ago - do a darn good job of reproducing observed changes. Learn more here: and see the data for yourself here:…
Today, acting EPA Admin Wheeler repeated the myth about the #NationalClimateAssessment being based on a “worst case” scenario (scan up this thread to see why that’s wrong) and added a new myth, that most of the report was written in 2016, under the Obama admin. It wasn’t.
I checked my own records, and I began Chapter 2 in May 2017 and sent the first draft to my co-authors on June 17. The entire report went out for public and National Academy review on Nov 3, 2017.
Wheeler also said that he “wouldn’t be surprised if the Obama administration told the report’s authors to take a look at the worst case scenario for this report,” an allegation that former OSTP director John Holdren categorically rejects:…
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