Harvey the Invisible Rabbit: Did not exist.
This is a picture of some men.
Since they are men, they have some abilities. They can, for example, knock each other over, and they can play with balls. This is what men do, and this is what these men can do.
They are also men. They can also knock each other over, and they can also play with balls. But the NFL football players are much better at knocking each other over, and you wouldn’t believe how great they are at playing with balls.
They are NFL enhanced. They are trained, embiggened with special diets, and they are clad with armor and vibrant, often scary, colors.
This is a picture of a hurricane from 1938.
It was a big one; It did lots of damage when it slammed into New England and New York.
A hurricane is a large storm that forms in the tropics, and sometimes hits land. The energy from a hurricane comes from a combination of the earth’s spin, trade winds, and so on, but mainly, from the heat on the surface of the sea. The rain that falls from the hurricane also comes mainly from the sea surface indirectly, and any water that evaporates into the atmosphere.
This is a picture of Harvey the Hurricane, the remnants of which are still circulating around in Texas.
Harvey is a lot like the 1938 hurricane, in that it formed in the tropics, in the Atlantic, and was a big spinny thing. It got its energy in the same way, and formed in the same way, and both slammed into land and scared the crap out of everybody.
But they are different, the 1938 Hurricane and Harvey the Hurricane. How are they different? Have a look at this map:
The pairs of photos above show “then” and “now” for two different things (men and hurricanes). This map shows both then and now in the same graphic. This map represents the current sea surface temperature anomalies, meaning, how much warmer or cooler the current sea temperatures are compared to the same time of year but at some time in the past, averaged over a long period, in this case, from 1971-2000. Global warming was well underway during that period, so present sea surface temperature readings that are above that baseline are not only high but are actually very high, because the baseline is high.
In this map, red is more, blue is less. Look at all the nearly ubiquitous more-ness in sea surface temperatures around the world. That causes the atmosphere across the entire globe to potentially contain much more water vapor than it could have contained during that that baseline period. Look at the sea surface temperature anomalies for the gulf of Mexico, where Harvey formed. They are high. This means that any hurricane that formed over that extra warm water will be stronger, and any tropical storm system that occurs pretty much anywhere on this map (or round the other side of the Earth as well, for that matter) will contain more water, than it would if it existed and all else was equal several decades ago.
This is a picture of a Unicorn.
A unicorn poops rainbows and pees mimosas. Or so I’m told. This is another view of Harvey the Hurricane.
What is the difference between the unicorn and Harvey? Harvey is real, and the unicorn is not.
I won’t quote you or give you links. Why? Because I find this whole thing a bit too embarrassing. But here is the thing. Otherwise intelligent and well informed individuals have stated in various outlets, including major media, and including twitter, that it is simply inappropriate to claim that Harvey the Hurricane is in any way global warming enhanced.
This is wrong. There is no such thing as a storm of any kind that is not a function of the current climatology. The current climatology has widespread and persistent, and in many cases alarmingly high, sea surface temperature anomalies. There will not be a tropical storm, including hurricanes, that escape the physics and poop out rainbows and pee mimosas. They will all be real. They will all have greater power and more moisture than they otherwise would have, had they formed decades ago before the extreme global warming we have experience so far.
There was a time when Harvey was a rabbit, an invisible rabbit only seen by a delusional character in a movie, played by Jimmy Stewart. Today, we have Harvey the Unenhanced Storm, playing that role. It is a fiction, something seen by a few but that is no more real than the above depicted unicorn.
As I was writing this post, Michael Mann posted an item in the Guardian that makes this case.
He says (click here for the whole story):
Sea level rise attributable to climate change – some of which is due to coastal subsidence caused by human disturbance such as oil drilling – is more than half a foot (15cm) over the past few decades … That means the storm surge was half a foot higher than it would have been just decades ago, meaning far more flooding and destruction.
… sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades from roughly 30C (86F) to 30.5C (87F), which contributed to the very warm sea surface temperatures (30.5-31C, or 87-88F).
… there is a roughly 3% increase in average atmospheric moisture content for each 0.5C of warming. Sea surface temperatures in the area where Harvey intensified were 0.5-1C warmer than current-day average … That means 3-5% more moisture in the atmosphere.
That large amount of moisture creates the potential for much greater rainfalls and greater flooding. The combination of coastal flooding and heavy rainfall is responsible for the devastating flooding that Houston is experiencing.
… there is a deep layer of warm water that Harvey was able to feed upon when it intensified at near record pace as it neared the coast….
Harvey was almost certainly more intense than it would have been in the absence of human-caused warming, which means stronger winds, more wind damage and a larger storm surge…
Mann mentions other effects as well, but I’ll let you go read them.
The extra heat at depth Mann mentions is now recognized as responsible for the extra bigness and badness of some other famous hurricanes as well, such as Katrina and Haiyan. Harvey might be a member of a small but growing class of hurricanes, deep-heat hurricanes I’ll call them for now, that simply did not exist prior to global warming of recent decades. Further research is needed on this, but that’s the direction we are heading.
Climate scientist Kevin Trenberth recently noted that “The human contribution can be up to 30 percent or so up to the total rainfall coming out of the storm,”
Aside from Michael Mann’s Guardian article, he has this facebook post making the same argument.
Harvey the Hurricane is real, and so was the 1938 Hurricane. Climate change enhancement of Harvey is real, but unicorns are not. Sadly.
I really thought we had stopped hearing this meme, that “you can never attribute a given weather event to climate change.” But, apparently not. That is a statement that is technically true in the same way that we can’t really attribute an Alberta Clipper (a kind of snow storm) to the spin of the Earth. Yet, somehow, the spin of the Earth is why Alberta Clippers come from Alberta. In other words, the statement is a falsehood that can never be evaluated because it is framed incorrectly. Here is the correct framing:
Climate is weather long term, and weather is climate here and now. The climate has changed. Ergo … you fill in the blank. Hit: Unicorns are not involved.