Thread by @RyanMaue

Now that everyone is back at work, the conversation about Hurricane #Dorian and climate change will begin in earnest. That's fine as long as you stick to sound science.

So, what is the current "consensus" among hurricane scientists?

It's right here: gfdl.noaa.gov/global-warming…

(1) It's important to point out that this 2019.

It is not the year 2100 and you should not take climate model output from 80-years in the future as the proof of a "signal" you are seeing today.

The changes in the 22nd Century are a long ways off.

(2) We have a long historical record -- going back to 1851 -- with, of course, decreasing certainty in hurricane data.

However, since the 1940s we have aircraft recon and then satellites came along in the past 50-years.

We also have good records of U.S. landfalls.

(3) Is there a climate signal with Hurricane #Dorian? --> Detection

Is this climate signal due to human-induced CO2 global warming? --> attribution

Framework: you should satisfy both.

(4) Observed sea level rise is surely a detectable result of global warming & is additive to hurricane caused surge. ✔️

What about more hurricanes ... more intense ... wetter ... or slower moving?

With #Dorian, focus is obviously upon the "stalling" over the Bahamas.

(5) There is some recent research on changes in hurricane movement speed (trend toward slower) -- but it is not understood what specific mechanism is causing this. In other words, a climate signal has been detected in hurricane statistics, but a physical reason still lacks.

(6) From a "weather point of view" we know why Hurricane #Dorian stalled. We can observe it, diagram it with maps, and successfully model the behavior days in advance -- hence why much of Florida remains safely in their homes.

Did climate change have an impact upon this?

(7) Good discussion here of the hurricane movement & climate question -- but there is quite general to historical trends. There has been no research specifically on Dorian ... just speculation about it "fitting a trend"

insideclimatenews.org/news/03092019/…

(8) A stalling hurricane over water (like Dorian) will eventually (24-36 hours) cause its own weakening. Cooler water from below will be mixed up to the surface -- the opposite of "high octane" fuel.

However, the rainfall will add up over a small area.

(9) Thus, scientists would need to look at the factors that went into the stalling of #Dorian --> the steering currents at 25°N latitude -- in the subtropics. And then, quantify if/how/why climate change affected this particular atmospheric configuration. Herculean task.

(10) Hurricane Michael rapidly intensified up until landfall in the Florida panhandle. That was arguable a consequence of its "fast movement" -- the complete opposite of stalling.

Two Category 5s in consecutive years -- slow vs. fast movement.

(11) The ocean surface temperatures in late summer are plenty sufficient for the most intense hurricanes -- including high-end Category 5 -- across a large portion of the Atlantic basin.

If all else is equal, then warming these ocean temperatures would allow for stronger storms.

(12) However, the Atlantic is currently a "marginal" hurricane basin that requires a lot to go right in order to spin up an intense storm.
You need a disturbance (usually an African Easterly Wave).
You need weak vertical wind shear.
You need instability + moist air.

(13) There is a societal need to understand if/how hurricanes are changing in the current climate -- and during the coming decades.
The answers -- or lack thereof -- will not satisfy most people. It's a mixed bag replete with uncertainty and caveats.

(14) The public should beware of overconfident assertions that diverge from the current expert consensus.

Some scientists are way too eager to make (tenuous) connections between hurricanes and climate change.

The media tends to amplify those voices.

(15) Let's consider this op-ed from the NY Times:
nytimes.com/2019/09/03/opi…

The capable author read the 4th National Climate Assessment report, collected some data, and then presented the results.

Does this effort reflect the current scientific consensus?

(16) 1st Sentence:

"The frequency of severe hurricanes in the Atlantic Ocean has roughly doubled over the last two decades, & climate change appears to be the reason. Yet much of the conversation about Hurricane Dorian — including most media coverage — ignores climate change."

(17) Frequency of severe hurricanes -- defined as Category 4's and 5's has doubled in the past 20-years.

e.g. comparison between 1980-1999 & 2000-2019

--> And climate change is the reason.

Seems pretty definitive. There's even a chart. The author is convinced.

(18) CBS News has an article with a shocking headline:

"Intense hurricanes like Dorian produce 1,000 times more damage – and they're becoming more common"

cbsnews.com/news/hurricane…

Let's look at the evidence in here:

(19) The author (@WeatherProf) -- a meteorologist does not cite the NOAA GFDL consensus but instead weighs the evidence himself.

The dots are connected between recent Category 5's and climate change.

Like the NY Times article, is it really this simple?

@WeatherProf (20) From the UK, here's what would probably be categorized as a "climate denial" article. Yet, it accurately relays what's in the current scientific consensus. 🤔

"The lazy assertion that Hurricane Dorian is caused by climate change"

blogs.spectator.co.uk/2019/09/the-la…

@WeatherProf (21) CNBC has a new article this time with a headline quote from climate scientist Michael Mann:

"Human-caused climate change is visibly intensifying hurricanes and increasing the damage they are doing"

@WeatherProf Another quote:
"Dorian stalling is consistent with the long-term trend driven by climate change,” said Jeff Nesbit, executive director of Climate Nexus and author of “This Is the Way the World Ends.”

cnbc.com/2019/09/03/hur…

(17b) My friend @jswatz steps up to the plate with his NY Times article on how Climate Change Affected Dorian.

nytimes.com/2019/09/03/cli…

The framing is more "evidence for" with Hayhoe and Francis, but includes some helpful balance from an actual hurricane scientist.