30/08/2017

Houston, You Have A Problem, And Some Of It Of Your Own Making

Fairfax - Peter Hannam

Yes, Houston, you do have a problem, and – as insensitive as it seems to bring it up just now – some of it is your own making.
Let's be clear upfront. I unreservedly wish that all of your millions of citizens get safely through Tropical Storm Harvey, and the biblical-scale deluge and floods that are forecast to swamp your city in coming days.

Harvey: Catastophic flooding continues
Houston is facing worsening historic flooding in the coming days as Tropical Storm Harvey dumps rain on the city, swelling rivers to record levels.

But, as the self-styled "world capital of the oil and gas industry", there's a connection between rising global greenhouse gas levels and the extreme weather now being inflicted that some of your residents have understood for decades and had a hand in.
Houston and its surrounds are home to some 5000 energy-related firms, 17 of which are counted among the Fortune 500 list of largest US companies.
The nearby Gulf Coast is also one of the biggest oil-refining centres anywhere. Not for nothing, the local football team was named the Houston Oilers before it up-rigged elsewhere to become the Tennessee Titans.
One thing that hasn't changed for almost 200 years is scientists' basic understanding humans could alter the chemistry of the atmosphere. By releasing more carbon dioxide, methane (also known as natural gas), and other greenhouse gases, the atmosphere would trap more heat and alter our climate in the process.
The links between fossil fuels and climate change – clear to all but a handful of (often industry-funded) scientists – were hardly promotional talking points oil firms have been keen to trumpet.
In fact, as an important research paper by Harvard University researchers Geoffrey Supran and Naomi Oreskes released last week showed, the largest of them – ExxonMobil – deliberately told the public a story at odds with their own research.



Houston Police SWAT officer Daryl Hudeck carries Connie Pham and her 13-month-old son Aiden after rescuing them from their home. Photo: AP
By stoking doubts about the climate change consequences of burning fossils, the behemoth misled voters for four decades, successfully stymieing demands for action in the US and abroad, including in Australia.
Although ExxonMobil is headquartered in another Texan city, Dallas, it bases many operations in Houston. The company has picked Houston to host a sprawling new campus north of the city that will reportedly house 8000 employees.
Hurricane Harvey as it crossed the Gulf coast on Saturday. Photo: NOAA
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Climate connection
Those seeking to discourage debate about Harvey's climate boost will argue there hasn't been a major (category three or stronger) hurricane crossing the continental US coast in almost 12 years.
Houses were left inundated in Rockport, Texas, with heavy rain still falling in the region. Photo: Alex Scott
Scientists and climate models, though, argue a warming planet won't necessarily equate to more frequent and more intense tropical cyclones in all basins every year. Decadal patterns are what you need to watch.
The western Pacific is one basin where scientists are increasingly confident of a discernable trend that is not good news for the large populations in China, Japan and the Philippines – among others – that are exposed. One study last year found as much as a four-fold increase in the number of super typhoons.
A photo taken from the International Space Station shows Hurricane Harvey over Texas on Saturday. Photo: Jack Fischer/NASA via AP
Indeed, scientists are increasingly able to tease out a global warming signal in extreme weather events of many kinds.
These include a study last year that found the probability of an extreme rainfall event in the central US Gulf Coast had increased 1.4 times because of anthropogenic climate change.
A separate study in 2013 examined, among others, the contribution of climate change to super storm Sandy, which left a damage bill of $US60 billion ($75 billion) across the north-eastern US in 2012.
"Our future scenarios of Sandy-level return intervals are concerning, as they imply that events of less and less severity (from less powerful storms) will produce similar impacts," the paper found. "Further aggravating, the frequency and intensity of major storms/surges are likely to increase in a warming climate."

Impacts made worse
Andrew King, a climate extremes research fellow at the University of Melbourne and the ARC Centre of Excellence for Climate System Science, said the complexity of cyclones makes it difficult to attribute climate change to events such as Hurricane Harvey.
"These are hard to simulate, extreme cyclones, on the grid scale of climate models," he says.
What is clearer, though, is a warming atmosphere makes heavy rainfall events more possible. Each degree increase allows the atmosphere to hold roughly 7 per cent more moisture.
Similarly, rising sea levels means any storm surge accompanying a cyclone will be worse. "Even a small increase in sea levels creates a big increase of the extent of a storm surge going inland," King said.
Sea levels are rising globally – at about 3.4 millimetres a year – as glaciers and land-based ice sheets melt, and warming oceans expand.
Michael Mann, a prominent US climate scientist based at Pennsylvania State University, noted in a Facebook post how unusually warm Gulf waters, provided the energy for Harvey's near-record rate of intensification as it neared the coast.
Mann also points to the unusually stationary nature of the hurricane, which is leading to a "seemingly endless deluge" that could dump as much as 1.3 metres of rainfall before it's done.
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"This pattern, in turn, is associated with a greatly expanded subtropical high pressure system over much of the US right now, with the jet stream pushed well to the north," Mann says. "This pattern of subtropical expansion is predicted in model simulations of human-caused climate change."
When the clean-up eventually begins in Houston and other regions battered and drenched in this week's tempest, questions about what protection will be needed for the next big storm will no doubt surface.
Given its unusual dependence on fossil-fuel industries, though, it will be interesting to watch if Houston queries – tactfully and delicately – its own contribution to the catastrophe.
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It's A Fact: Climate Change Made Hurricane Harvey More Deadly

The Guardian - *

We can’t say that Hurricane Harvey was caused by climate change. But it was certainly worsened by it
A family evacuate their home after flooding from Hurricane Harvey, Houston, Texas, 27 August. Photograph: Joe Raedle/Getty Images
What can we say about the role of climate change in the unprecedented disaster that is unfolding in Houston with Hurricane Harvey? There are certain climate change-related factors that we can, with great confidence, say worsened the flooding.
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 (see here for a decent discussion). That means the storm surge was half a foot higher than it would have been just decades ago, meaning far more flooding and destruction.
In addition to that, 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 simple thermodynamic relationship known as the Clausius-Clapeyron equation that tells us 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 temperatures, which translates to 1-1.5C warmer than “average” temperatures a few decades ago. 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.
Not only are the surface waters of the Gulf of Mexico unusually warm right now, but 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. Human-caused warming is penetrating down into the ocean. It’s creating deeper layers of warm water in the Gulf and elsewhere.
Sea surface temperatures in the region have risen about 0.5C (close to 1F) over the past few decades
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. (As an example of how this works, we have shown that climate change has led to a dramatic increase in storm surge risk in New York City, making devastating events like Hurricane Sandy more likely.)
Finally, the more tenuous but potentially relevant climate factors: part of what has made Harvey such a devastating storm is the way it has stalled near the coast. It continues to pummel Houston and surrounding regions with a seemingly endless deluge, which will likely top out at nearly 4ft (1.22m) of rainfall over a days-long period before it is done.
The stalling is due to very weak prevailing winds, which are failing to steer the storm off to sea, allowing it to spin around and wobble back and forth. This pattern, in turn, is associated with a greatly expanded subtropical high pressure system over much of the US at the moment, with the jet stream pushed well to the north. This pattern of subtropical expansion is predicted in model simulations of human-caused climate change.
More tenuous, but possibly relevant still, is the fact that very persistent, nearly “stationary” summer weather patterns of this sort, where weather anomalies (both high-pressure dry hot regions and low-pressure stormy/rainy regions) stay locked in place for many days at a time, appears to be favoured by human-caused climate change. We recently published a paper in the academic journal Nature on this phenomenon.
In conclusion, while we cannot say climate change “caused” Hurricane Harvey (that is an ill-posed question), we can say is that it exacerbated several characteristics of the storm in a way that greatly increased the risk of damage and loss of life. Climate change worsened the impact of Hurricane Harvey.

 *Michael E Mann is distinguished professor of atmospheric science at Pennsylvania State University, director of the Penn State Earth System Science Center and author of three books, including The Hockey Stick and The Climate Wars, Dire Predictions, and The Madhouse Effect.

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Is Hurricane Harvey A Harbinger For Houston’s Future?

The Conversation - 

Houston’s Interstate Highway 45 was totally submerged in the deluge. REUTERS/Richard Carson
Over the past week we have seen two major tropical storms devastate different parts of the world. First Typhoon Hato struck Hong Kong and Southern China killing at least a dozen people. And over the weekend Hurricane Harvey made landfall from the Gulf of Mexico, bringing extremely heavy rain to southern Texas and causing devastating floods in Houston.
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Tropical cyclones are, of course, a natural feature of our climate. But the extreme impacts of these recent storms, especially in Houston, has understandably led to questions over whether climate change is to blame.

How are tropical cyclones changing?
Tropical cyclones, called typhoons in the Northwest Pacific and hurricanes in the North Atlantic, are major storm systems that initiate near the Equator and can hit locations in the tropics and subtropics around the world.
When we look at the Atlantic Basin we see increases in tropical storm numbers over the past century, although there is high year-to-year variability. The year 2005, when Hurricane Katrina devastated New Orleans, marks the high point.
There is a trend towards more tropical storms and hurricanes in the North Atlantic. US National Hurricane Center LARGE IMAGE
We can be confident that we’re seeing more severe tropical cyclones in the North Atlantic than we did a few decades ago. It is likely that climate change has contributed to this trend, although there is low statistical confidence associated with this statement. What that means is that this observed increase in hurricane frequency is more likely than not linked with climate change, but the increase may also be linked to decadal variability.

Has Harvey been enhanced by climate change?
Unlike other types of extreme weather such as heatwaves, the influence of climate change on tropical cyclones is hard to pin down. This is because tropical cyclones form as a result of many factors coming together, including high sea surface temperatures, and weak changes in wind strength through the depth of the atmosphere.
These storms are also difficult to simulate using climate models. To study changes in tropical cyclones we need to run our models at high resolution and with interactions between the atmosphere and the ocean being represented.
It’s much easier to study heat extremes, because we can do this by looking at a single, continuous variable: temperature. Tropical cyclones, on the other hand, are not a continuous variable; they either form or they don’t. This makes them much harder to model and study.
Tropical cyclones also have many different characteristics that might change in unpredictable ways as they develop, including their track, their overall size, and their strength. Different aspects of the cyclones are likely to change in different ways, and no two cyclones are the same. Compare that with a heatwave, which often have similar spatial features.
For all these reasons, it is very hard to say exactly how climate change has affected Hurricane Harvey.

So what can we say?
While it’s hard to pin the blame for Hurricane Harvey directly on climate change, we can say this: human-caused climate change has enhanced some of the impacts of the storm.
Fortunately, in Harvey’s case, the storm surge hasn’t been too bad, unlike for Hurricanes Katrina and Sandy, for example. This is because Harvey did not travel as far, and weakened rapidly when it made landfall.
We know that storm surges due to tropical cyclones have been enhanced by climate change. This is because the background sea level has increased, making it more likely that storm surges will inundate larger unprotected coastal regions.
Building levees and sea walls can alleviate some of these impacts, although these barriers will need to be higher (and therefore more expensive) in the future to keep out the rising seas.
Rockport, Texas, was one of the coastal towns flooded by Hurricane Harvey. EPA/Darren Abate
Deluge danger
Harvey’s biggest effect is through its intense and prolonged rainfall. A low pressure system to the north is keeping Harvey over southern Texas, resulting in greater rainfall totals.
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The rainfall totals are already remarkable and are only going to get worse.
We know that climate change is enhancing extreme rainfall. As the atmosphere is getting warmer it can hold more moisture (roughly 7% more for every 1℃ rise in temperature). This means that when we get the right circumstances for very extreme rainfall to occur, climate change is likely to make these events even worse than they would have been otherwise. Without a full analysis it is hard to put exact numbers on this effect, but on a basic level, wetter skies mean more intense rain.

Houston, we have a problem
There are other factors that are making this storm worse than others in terms of its impact. Houston is the second-fastest growing city in the US, and the fourth most populous overall.
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As the region’s population grows, more and more of southern Texas is being paved with impermeable surfaces. This means that when there is extreme rainfall the water takes longer to drain away, prolonging and intensifying the floods.
Hurricane Harvey is likely to end up being one of the most costly disasters in US history. It is also likely that climate change and population growth in the region have worsened the effects of this major storm.

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