Yes, Climate Change Made Hurricane Harvey Worse

"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."


By Michael E Mann, distinguished professor of atmospheric science at Pennsylvania State University, for The Guardian

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.

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 Scientific Reports 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.


11 comments on “Yes, Climate Change Made Hurricane Harvey Worse

  1. Michael Mann misses the main reason for the serious devastation of Harvey. Stalled hurricanes and massive flooding are hardly unknown in the Gulf Coast area. In fact while some area river gages set records with this storm, many did not. And the historical record for gages data rarely exceeds 100 years, meaning that the statistical foundation lacks depth for understanding the frequency of larger events.

    Fact is, the pressure to develop and live in flood-prone areas overwhelms the sagacity to only develop secure terrains. The promise of safety to build in the protection of civil works, e.g. dams, has a weak foundation due to underestimation and lack of understanding of risks, irrespective of the role of AGW climate change.

    Look up the safety concerns on the Barker-Addicks structures and why the ACE had to make intentional releases. A friend of mine got flooded out on account of these releases.

    And for those that do not follow the debate carefully, it is fair to point out that Michael Mann as a reference and commentator resides pretty far to “left” on the topic of the severity and consequences of climate change and human role in its cause. “Left” in this case implies flamboyant and hysterical; usually those referencing Michael Mann have an axe to grind on the “left” side of the political spectrum, or are just looking for hysterical headlines to juice clicks and readership (looking at you “The Guardian”).

  2. Curt A Tyner

    Well another fool creating some mythical left/right over a fu*king raindrop. Storms are always going to be with us raindrops don’t care if you deny science they will fall whether you make your silly arguments of denial or not. The planet is warming and the reason we Know this is science and math. So stop with that weak left/right whining bullsh*t. Science,measurements,math tell us 15 of the last 17 years have been the hottest ever recorded. Sorry if that is a problem for you, it is a major problem for the rest of us . So do something about it or get out of the way and let the rest of us fight this battle.

    • Well Curt since there are no other comments so far, it appears that you have directed your comment to my comment.

      I guess that you missed its point as it is agnostic to climate change, AG or otherwise.

      The main point is that underestimation of such events related to such as flood potential, storm surge and the development pressures to build in marginal areas with respect to flood plains more significantly contributes to misery with Harvey than the effects described by Michael Mann. As you said, it’s counting rain drops. Nobody would much care whether 1 trillion raindrops fell or 1.1 trillion if they didn’t have their house in the geologic floodplain.

      While politicians and others argue back and forth about the proper responses to “combat” climate change, Rome burns in the civil infrastructure and zoning/land-use arena.

      And BTW, if one accepts the accuracy or probability of climate models in the terms expressed by Michael Mann, then the urgency to address the above matters only increases.

  3. I’m quite sure that “climate change” (always changing – with and without human inputs) and have increased precipitation rates – add heat and you get more evaporation when that evaporation cools in the upper atmosphere you get rain, more rain in some areas. However, teasing the mathematically correct amount of heat input effect from any event is beyond our abilities due to the almost unlimited variable associated with those calculation. So, yes a warmer world will have higher levels of precipitation as it balances increased heat inputs. I have no idea whether and to what level the current flooding in Texas is associated with anthropogenic climate change. As we continue to over populate the face of the earth with more and more humans every year, it is only logical that the high ground availability becomes less available. You get lots of humans in low lying areas as result. Extreme weather events tend to highlight just badly we humans plan, and the many important details we ignore in our lives. We should not be surprised when once in a 100 year weather events point out lack of attention to important details – like the elevation of our homes. We should also not use these events independent of accurate historical comparison based interpretations.

    From a mass balance (very simplistically – all inputs = all outputs) perspective it is almost impossible to combust most of 90 million barrels of petroleum a day as global humans do – without that heat input having some effect on climate. Add to that increased heat absorption of the human reflective alterations of the surface of the planet (black pavement, roof tops, bare ground/deforestation, etc) and clearly the heat inputs to the planet have been significantly altered by global human activities. However, projecting exactly how much and severe those inputs will be expressed in balancing mechanisms of the earth’s climate control system is extraordinarily difficult given the lack of precise historic and even current data. Even our best satellite weather data still requires constant human “re-calibration” and “reinterpretation.”

    Most of us are aware of climate change deniers. However, these folks’ beliefs generally lack an informed and educated perspective and most are generally based on political cultism – rather than critical thinking. On the other side you have those that see climate change, global warming, etc. as a cause celebre embracing every disaster as proof of their thesis – and also fail the basics of critical thinking.

    Basics physics tells us that basic planetary energy releases by humans are significant compared to periods prior to the Industrial Revolutions of the past two hundred years. Meaning that logically denying the mathematical impacts of this human energy input is logically impossible. On the other side making dire projections of how these impacts with effect climate balances is no less logical. Our planet has an amazing ability of adjust the climate to extremes of heat inputs through the evaporative cooling cycle. Even with and regardless of the “gee whiz” results of “limited” and “adjusted” computer modeling attempts and while change in the current climate may indeed be discernible – its long term effects are much less so. Consequently, we have to be very weary of the two sides of the climate change discussion, their political and ultimately their financial motivations – and not ignore both sides’ ability at distorting the very limited interpretations historical comparative data (especially proxy data) that we have and or projecting their assumptions far beyond our best data’s meaningful levels of accuracy.

    There have been and continue to be numerous cases of individuals so dedicated to their climate and environmental causes that they are willing to sacrifice their own and their causes credibility just to gain more influence in the media and the public mind. For example – my favorite example agenda driven information:

    “2009 investigative report from UK’s Telegraph detailed the extent of dictatorial-like powers Connolley possessed at Wikipedia, allowing him to remove inconvenient scientific information that didn’t conform to his point of view.”

    “All told, Connolley created or rewrote 5,428 unique Wikipedia articles. His control over Wikipedia was greater still, however, through the role he obtained at Wikipedia as a website administrator, which allowed him to act with virtual impunity. When Connolley didn’t like the subject of a certain article, he removed it — more than 500 articles of various descriptions disappeared at his hand. When he disapproved of the arguments that others were making, he often had them barred — over 2,000 Wikipedia contributors who ran afoul of him found themselves blocked from making further contributions. Acolytes whose writing conformed to Connolley’s global warming views, in contrast, were rewarded with Wikipedia’s blessings. In these ways, Connolley turned Wikipedia into the missionary wing of the global warming movement.“

    Connolley was removed from the editorial responsibilities at Wikipedia, but only after this report. Connolley continues to be a very sensitive topic with Wikipedia and one they would prefer – but should not forget. However, the Connolly’s of this world aren’t limited to Wikipedia (I like and support Wikipedia) from being on the staff of other encyclopedias, news organizations, and or political movements.

    Some where in the middle of the climate discussion is where we all live, adapt or not, and try to make the best life possible. It’s a tricky middle ground at best.

  4. Anonymous

    Hey, you two – Curt and JBond – quit trying to tie this Houston and other coastal area flood into some side of your arguments about how all this happened. How about this: sea level areas plus up to 50 inches of rain, non-stop for a week, period. Some folks like to live close to the water and understand the “risk” and also have knowledge of normal behavior of hurricanes (ha! totally unpredictable!). Many of these people make a living in occupations that are only found in sea level areas. Fishing. Ports, for ships – both commercial and pleasure. Once you have people in areas for work, they need housing. More people, more housing. More people and housing, need more businesses such as grocery stores, pharmacies, medical, entertainment, etc. It is not really complicated. Growth. And you cannot build a wall to keep that out. Most of the world depends on growth and what is produced by growth. Price of goods is based on availability — import/export by rail, road or sea. This terrible and frightening historical event will reverberate across our Nation for many years.

    So you guys and others can sit opposite sides of the table and argue until you are dead. Perhaps science and math will help determine how to build but it will never stop the growth. Sometimes it is really just as simple as Noah saw it.

    – Murphy

    • Thanks Murphy for the advice. I have no horse in this race except having a friend affected by it and to the extent that we are all affected by “the climate” and the impulse of some people to profit by pushing the zoning envelope. And you’re right, growth and the desire to live and work somewhere is a strong force. It happens that I have experience in hydrology and follow closely NWS river hydrographs. Also my wife is a local community activist and has much experience being threatened by developers trying to bend the rules with more-or-less complicity on the part of municipal officials mostly interested increasing the tax base irrespective of the long-term risks.

      • Anonymous

        JBond, I applaud your wife! So much of all levels of government is corrupt – for profit. asswipes, all of them. I don’t even know what your job means? haha! My “horse in this race” is I live in Houston and have for 70 years. I have watched the growth. My home is located in a subdivision that used to be a farm – cattle were still roaming my street when I moved into it, 45 years ago! Also, a huge rice farm – so you may know that growing rice is done in flooded fields. Now, all residential, big and expensive homes…oh, and Buffalo Bayou runs right through it! So my “horse” is struggling.

        – Murphy

  5. Anonymous

    For ya’ll interested in how this all happened in Houston and some related historical 1935 film footage, all presented by Rachel Maddow last night, I think you will really find this interesting!

    – Murphy

    • Thanks Murphy for the link. Are you safe? Did you evacuate?

      • Anonymous

        JBond – thanks for asking! Yes, I’m good. Not perfect, but good. Better than a million others for damned sure! Half my subdivision flooded, some 6 ft deep inside the homes – those are all around a little private “lake”, we call it The Lake Section (so clever, huh?) and they are heavily insured, bet on it (multi-million dollar homes, maybe 80) and as the community drifts back toward my location, less damage, less mortgage, flooding up to front doors and maybe some with water inside (200?) and eventually you get to my street and water into front yards maybe 10-20 feet but not inside home (500?); no power for 3 days so I found a cozy place to run to. I must have power for this oxygen tank that follows me around! Never seen anything like it and been thru a bunch of hurricanes and city floods but not like this! Some neighbors who finally bailed had to drive all the way to San Antonio to get away from flooding and find a hotel. There are about 20,000 they say in shelters all around the city – and more shelters and more flooding in many other towns south of us and then up the coast all the way into Louisiana. Entire subdivisions completely flooded. National Guard all over the place. Anyone who is not flooded out and even some that are, all working to help the ones that are worse off. Helicopters flying around now shooting showing videos that will leave you speechless! Two dams with controlled releases to prevent bursting, adding more damage to homes downstream. One of those damned if you do and damned if you don’t situations. I am very comfy with a big window into a sunny dry green courtyard with a fish pond and waterfall…so good I feel guilty! Here’s a local tv station with tons of good videos – we will be glad when the tv stations get back to the routine shows! Nothing but non-stop coverage, all day, all night, for a week. Here’s the good stuff

        – Murphy 🙂

    • Three 500-yr floods in the last “x” years?

      Whether it’s climate change or faulty estimation of possible floods… Houston, we have a problem…

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