It’s the bomb

A friend asks “So what is up with this bomb cyclone term? Is it just a blizzard with a more compelling name? Or is it something unique that I have not experienced before now? Is bomb cyclone a technical term?”

Answer: like “polar vortex”, “bomb” is a term that has been used by meteorologists for many years but is just now being brought into popular usage by weather media. It refers to a winter storm over the ocean that strengthens very rapidly – the technical requirement is that the minimum surface pressure drops by at least 24 hectopascals (hPa, also known as millibars, or mb) in 24 hours. The term was brought into the scientific literature by Fred Sanders and John Gyakum in a 1980 paper, here:…/1520-0493(1980)108%3C1589%3AS…

a less technical and more recent discussion is here:…/is-bomb-cyclone-even-a-real-t…

a bit more history and some quotes from Gyakum:…/bomb-cyclone-definition_us…

And if you want to know more about the polar vortex while you’re at it: Darryn Waugh, Lorenzo Polvani and I wrote an article about that term for the Bulletin of the American Meteorological Society that is a bit more scientific than what you’ll find in the mass (or social) media, but more accessible than a typical peer-reviewed research article:

Harvey commentary

Some further commentary on Harvey. Mostly (but not all) about the climate connection.

Global Warming’s Role in Hurricane Harvey (The Takeaway, NPR)

Why Harvey’s devastation is so severe (CNN)

Climate Change Didn’t Cause Hurricane Harvey, but It Made It Worse (Fortune)

Commentary by Columbia Scholars (not just me)

Meanwhile, Hurricane Irma is breaking records and looking truly fearsome in the Atlantic.

Mandatory Harvey evacuations are justified

Science can make predictions, but government has to act on them or they aren’t any use.

On Wednesday evening, Harvey was still just a tropical depression with winds of 35 miles per hour. The National Hurricane Center forecast that it would intensify to 40 miles per hour by Thursday morning, and reach its peak intensity two days later at 75 miles per hour – just barely crossing the threshold to be called a hurricane – just before landfall.

By 10 AM Central on Thursday, the picture had radically changed. The storm’s winds had already jumped up to 65 miles per hour, and the rapid intensification was forecast to continue, with Harvey reaching 115 miles per hour – category 3 on the Saffir-Simpson scale – before landfall. With these more intense winds came a prediction of 6-10 feet of storm surge for parts of the Texas coast, and an increase in forecast rainfall, with potential for up to two feet in some locations. Suddenly Harvey looked likely to produce a major disaster.

The machinery of government, media, and private sector began to engage, with emergency preparations and warnings ramping up to amplify the State of Disaster already issued Wednesday for 30 counties by Texas’ Governor.

Harvey was still just a tropical storm at this moment. All the emergency actions were predicated on forecasts of future changes in Harvey’s intensity. Intensity prediction is normally considered the weak point in the science of hurricane forecasting, and rapid intensification just before landfall, in particular, has often been called a “forecaster’s nightmare”. But the forecasters predicted it with confidence, and no one, as far as I know, questioned that prediction. The conditions were right, with sea surface temperatures in the Gulf very warm and vertical wind shear (the difference in the steering winds at different heights that can disrupt a hurricane’s circulation) very low. With landfall still somewhere between 36 and 48 hours away – not nearly as much lead time as would be ideal, but enough for many life- and property-saving actions – the NHC’s experts were able to sound the alarm effectively.

The forecasts quickly proved right. Harvey is closing in on the coast near Corpus Christi, and NHC a few hours ago declared it a category 3 Major Hurricane, with sustained winds now up to 125 miles per hour. A storm with winds of this magnitude has not made landfall in the US in over 11 years, but that “drought” will almost certainly end tomorrow.

These forecasts are a scientific success story, but their value depends on the actions of the state, local and federal governments.

Corpus Christi, a city of 325,000 people, is directly in Harvey’s sights. Much of the city – and all of its oil refineries – lie close to the water on a bay that can funnel and amplify the surge, now forecast to be between 6-12 feet (it’s already more than 4 feet as I write). The flooding will come with winds well in excess of hurricane force, and will likely be exacerbated and prolonged by heavy rains that could continue for days.

Yet on Thursday, the Mayor of Corpus Christi decided not to issue a mandatory evacuation order, but instead just to “encourage” evacuation of residents in the lowest-lying areas. I can’t understand this decision.

In a press conference this morning, the Mayor stood by it. When a reporter asked how many people might be left in the areas most at risk, the Mayor replied that he didn’t know, as there’s no way at this moment to take a survey. That’s probably true, but it would have been better if he could have said “we’re doing everything possible to get every one of those people out of harm’s way”. He couldn’t say that, because he hadn’t.

The motivation for avoiding a mandatory order appears to have been a fear of risking first responders’ lives by sending them in to enforce it. But there was no need to send them in. In the United States, a mandatory evacuation order is almost never truly mandatory in that sense. The Mayor could have simply said it was mandatory, and warned everyone in Harvey’s path that if they stayed in defiance of it, no one would be able to come and help them.

How many more people would have evacuated if the order had been mandatory? It’s impossible to know. Some won’t leave no matter what. But it’s hard to imagine that it wouldn’t have made a difference to some people if they’d heard their Mayor tell them they have to leave now, rather than just that it seems like a good idea.

By now, it is probably too late for anyone to get out who hasn’t already. I hope not many are left, and for those who are, I hope Harvey’s impacts turn out less catastrophic than predicted. Corpus Christi may get some luck yet – as I write, the latest forecasts have the center coming in very close to the city, which could put the strongest winds and surge just to the east. Several of the closest counties on that side have issued mandatory evacuation orders; some have not.


False Uncertainty

The New York Times wants to promote dialogue between left and right on climate. This is a worthy impulse. And the person they have hired towards this end, a conservative journalist with a history of climate denial, states in his first piece for the Times that he accepts as “indisputable” the human influence on the observed warming of the earth since the late 19th century. Good.

The rest of Stephens’ piece, though, is a stew of innuendo and misdirection, in service of no apparent goal beyond a smug scolding of some unnamed others’ perceived “100% certainty” on climate.

Who and what is Stephens talking about? The entire climate science literature, including the 2014 IPCC Report (which Stephens cites), is full of statements about uncertainty about virtually all aspects of future climate change. What climate scientist or credible policy maker has ever claimed anything is 100% certain? It would be great if a conservative writer who accepts the science on climate would engage, seriously and sincerely, with real arguments made by credible climate scientists and advocates of climate action on the pages of the Times. Stephens, instead, takes the lazy route, arguing with straw men.

Stephens shows no interest in making constructive arguments in defense of any actual position. He doesn’t articulate any specific view on climate policy, which is what really ought to matter to Times readers of any political persuasion. But one is left to assume he thinks we don’t need to do anything about global warming. Why? Because nothing is 100% certain.

This passes for substantive argument in some circles. Though his acceptance of scientific fact – at least in this piece, if not his prior work – distinguishes him from the climate deniers at the Heartland Institute and Heritage Foundation, Stephens’ strategy is nonetheless the same cynical one as theirs: promote doubt, nothing more. He seems to be saying that liberals (or someone) should be more tolerant of conservative “skepticism” on climate, but that skeptics have no need to justify their views (or even to have any), because it’s ok just to be generally skeptical.

And Stephens is uninterested in applying any of this skepticism to the claims of those opposed to climate action. Presumably referring to (unnamed) proposals for reducing greenhouse gas emissions, he writes that “Demanding abrupt and expensive changes in public policy raises fair questions about ideological intentions.” Leaving aside the crass culture-warring tone – saying those who are in favor of climate action are “demanding” while those opposed are just “raising fair questions” is particularly absurd under the current regime in Washington – how well do we know how expensive any proposed climate policy is? Predictions of the economic impacts of climate policies are far more uncertain than climate projections. The price of renewable energy is dropping much more rapidly than nearly anyone expected a few years ago. Isn’t there some excessive certainty here that could benefit from self-examination?

Perhaps what Stephens means by “100% certainty” is the passion among many for the view that the evidence of a human influence on climate is sufficient to merit a serious policy response. This passion does not require absolute certainty on any aspect of the science, just an intellectually honest view of risk. Because what the genuine uncertainty on climate really means is that while there is a chance future climate change won’t be as bad as the projections say is most likely, there is also a chance it will be much worse.

In no other area of life do we respond to risks by simply assuming the best case scenario. We take out insurance on our homes not because we are 100% certain they will burn down, but because there is a chance they might. Climate should be no different – except that the situation now is more like one in which a wildfire is already spreading towards our house, and we’re just debating whether it will singe the house a little or consume it entirely. How is skepticism a justification for inaction, as long as one accepts at least some possibility that the science is right?

This is the fundamental dishonesty of Stephens’ piece, and of all those who justify inaction by claims of skepticism. It makes no sense to be opposed to any action to mitigate global warming just because there is uncertainty in climate projections. The only way it makes sense is if you’re certain the science is entirely wrong. Or, though maybe you don’t want to say it, you just don’t care, because you’re pretty sure it won’t affect you personally. That is the true false certainty, masquerading as skepticism.

Thanks to Emmanuel Vincent of Climate Feedback for asking me to write this.

Warn on the hazard

In this article, Andrew Freedman of Mashable argues that the Saffir-Simpson scale should be changed because it doesn’t measure rainfall, and yet rainfall causes disasters in many hurricanes – including Matthew in North Carolina just now. The Governor of North Carolina has been saying the same thing. The National Weather Service disagrees, and so do I.

In fact the Saffir-Simpson scale used to be based on not just wind, but also pressure and storm surge. It was simplified to just wind a while back because the different variables often wouldn’t match for a single storm – e.g., Sandy would have been a cat 1 due to wind but a cat 3 due to surge. There is no way to make a single number capture all the different hazards without being confusing. You wouldn’t know just from the number what the reason for the number was, and would still have to read the fine print in the forecast to find that out.

In addition, heavy floods can happen from storms that are not tropical cyclones at all. E.g., Louisiana a couple months ago. How would a change to the Saffir-Simpson scale help with those?

The rational approach is to warn on the hazard. That is, de-emphasize the Saffir-Simpson category, and issue warnings about each specific hazard separately. This is in fact the direction the National Weather Service (including the National Hurricane Center) has been moving. For example, they have recently introduced Storm Surge Watches and Warnings.

The NWS system can surely still be improved – apparently, the NWS forecasts of heavy rain didn’t reach everyone in North Carolina, even though they did exist and were quite accurate. So it would be reasonable, for example, for NHC to issue a formal Heavy Rainfall Watch or Warning (or whatever one wants to call them) when it is warranted in association with a tropical cyclone.

But multiple hazards from a tropical cyclone will remain multiple hazards. Combining them into one number wouldn’t eliminate the need for people in harm’s way to understand that. It would just disguise the problem, and disguising problems isn’t usually the best way to solve them.