August 26, 2017

experts react to hurricane harvey

Experts comment on Hurricane Harvey and its impact.

Prof Sir Brian Hoskins, Chair of the Grantham Institute for Climate Change at Imperial College London and Professor of Meteorology at the University of Reading, said:

“The fuel that produces the energy for tropical cyclones like Harvey is the heat stored in the near surface ocean. The more warming that occurs, the more fuel there is, and so the greater the intensity that tropical cyclones could potentially reach. Also the warmer air can hold more water, about 7% for every degree, and so the same storm will produce more intense rainfall. Warming is leading to the sea level rising at a rate of about 3cm per decade, increasing the likelihood of storm-surge damage.

“Harvey is unusual because it continued to strengthen in the Gulf of Mexico until it made landfall.  This is almost definitely linked to the anomalously high sea surface temperatures there as it developed. It is also unusual because the swirling winds in a tropical cyclone usually bring up cooler waters from below, which makes a stationary tropical cyclone decay quite quickly – but this did not happen. The long life of Harvey may have been possible only because the Gulf waters are also much warmer than usual below the surface – more research is necessary on this.

“Climate change due to increased greenhouse gases in the atmosphere makes the occurrence of the warm waters in the Gulf of Mexico (and elsewhere) more likely, and so it has increased the chances of occurrence of a hurricane like Harvey, and the devastating impacts that go with it.

“There is also no doubt that the flooding of Houston has been made much worse by the covering of grassland with tarmac and concrete – the natural drainage systems have been lost.”

Dr Jeffrey Kargel, Department of Hydrology & Atmospheric Sciences at the University of Arizona, said:

“As a glaciologist and planetary scientist, I recognize that the gears and switches of planets are not all understood, but it is clear that they do work as a system.  In Earth’s heat waves and retreating glaciers, we see the effects of global climate change. But another effect is also impacting much of the land surface: storm tracks are shifting. Some areas are getting drier, some wetter, but primarily there is more precipitation around the world, because as the sea surface warms due to accumulating atmospheric greenhouse gases, it evaporates more. That moisture is dumped onto the land as snow and rain.  Hurricanes always generate lots of rain.  But one trend ought to be taking place– the maximum sizes of hurricanes should be increasing, and with that their torrents of rain should be increasing.

“Whether we can attribute Harvey to global warming, as with any individual weather event, is a questionable proposition.  But it is very likely that many more storms like Harvey and Katrina and bigger ones yet are on the way; the expected higher frequency of such storms is an effect of global climate change brought on mainly by burning of fossil fuels. It seems an incredibly poor time to be killing flood regulations in construction of critical infrastructure. It is a decision likely to spur future losses of life and prosperity.”

Prof Stephen Belcher, Chief Scientist at the Met Office, said:

“The mechanics of tropical cyclones and how they interact with our changing climate is extremely complex. There is strong evidence that increasing sea temperatures increase the intensity of tropical storms when they develop. Rising sea levels also increase the risk of coastal flooding. When it comes to the frequency of these storms, it’s a much more challenging picture. At the moment we can’t say how all the different factors will combine to increase or decrease the number of storms we see.”

Julian Heming, tropical cyclones expert at the Met Office, said:

“The unprecedented rainfall from Hurricane Harvey is heavily influenced by blocking area of high pressure preventing the system from moving inland, concentrating the rainfall nearer the coast. The fact that the storm stalled just a little way inland and has indeed moved back out to sea means it has been able to collect more moisture from the sea and dump it inland.”

Dr Ilan Kelman, Reader in Risk, Resilience and Global Health at the Institute for Risk and Disaster Reduction and Institute for Global Health, UCL, said:

“As the continuing horror of Hurricane Harvey’s impacts unfold with the death toll sadly rising, it becomes increasingly apparent that this is not a natural disaster. When we build a city or build a dam, we must understand and deal with possible vulnerability to flooding at that point. By the time a storm forms, it is too late.

“The emergency responders and everyone helping out have done an incredible job. Nothing more could be asked of them. But emergency response to deal with people and houses in a floodplain is too late. Hurricane Harvey unfortunately shows yet again how decades of development and politics, which do not factor in environmental extremes, then causes a disaster.

“The hurricane is a natural event. The hurricane disaster comes from society, not from nature.”

Prof Richard Allan, Professor of Climate Processes at the University of Reading, said:

“There is a question of whether human-caused climate change has been a factor in this devastating storm. If the same conditions that caused the storm had occurred in a world without the warming observed over the last century, it would not have been as severe. A warmer ocean and the air above were able to inject greater quantities of moisture into the storm leading to intensification of already extreme rainfall. Additionally, sea level rise driven by climate warming combined with coastal subsidence related to human activities increased the storm surge while urban development such as paving over grasslands and prairies are likely to have exacerbated flooding.

“The dynamics of the storm are also curious but cannot easily be linked to climate change. When storms like this one move inland, they tend to die off. However, lingering near the coast where it has been, Hurricane Harvey maintained a healthy energy supply and has been able to continue picking up moisture and dumping it over land through sustained and intense rainfall.

“We can’t say that climate change ’caused’ Hurricane Harvey but the severity of the storm and associated damage was worsened by human activities, particularly the substantial emissions of greenhouse gases that are warming the oceans and the air above.”

Prof Dave Reay, Professor of Carbon Management at the University of Edinburgh, said:

“The scenes from Texas are shocking. Such extreme rainfall events are likely to get even more intense as our climate warms. When the flood waters finally recede, and the rebuilding of homes, businesses and lives begins, climate resilience needs to be front and centre.  Flood defence plans based only on past events will become obsolete as our warming atmosphere delivers much more rain and much more often. President Trump may have withdrawn the US from the Paris Climate Agreement, but he can’t opt out of the laws of physics.”

Prof Mike Hulme, Professor of Geography at the University of Cambridge, said:

“It’s important to separate out different elements the Houston flooding rather than simply saying ‘climate-change caused it’.  There was the Category 4 hurricane hitting land (unexceptional), the sustained heavy rainfall (exceptional), the exposure of the city to flooding and then the emergency response (little to do with ‘climate change’ as such).

“And we also need to be clearer about offering ‘climate-change’ as a causal factor.  Humans are changing the atmosphere in many different ways – emitting greenhouse gases, aerosols and smoke, changing the reflectivity of the land, and so on – each of which has different effects on the weather.  Rather than climate-change being a catch-all explanation for everything wrong with the weather, public and scientific commentary about the human influences on weather disasters needs to be much more nuanced.”

Prof Tim Palmer, Royal Society Research Professor at the University of Oxford, said:

“What has made Harvey so disastrous for Texas is the fact that it has stalled and the circulation patterns are continuously feeding moist air from the Gulf of Mexico up over Texas. So perhaps the single most important question for attributing Harvey to climate change is whether such stationary hurricanes will become more commonplace in the future.

“This is a question about possible changes in circulation and hence dynamics, rather than changes in the moistness and warmth of the air per se and hence thermodynamics. Unfortunately it is not a question that can be answered with a great deal of confidence from current-generation global climate models since their spatial resolution is typically inadequate to address such regional matters with any degree of reliability. There is still uncertainty about many aspects of the dynamics of climate change, and this will only be addressed by investment in climate models and the top-of-the-range supercomputers needed to run them. This is an area where UK scientists must continue to collaborate strongly with their colleagues in Europe.”

Dr Ilan Kelman, Reader in Risk, Resilience and Global Health at the Institute for Risk and Disaster Reduction and Institute for Global Health, UCL, said:

“As Hurricane Harvey’s devastation is revealed, we must ask how those affected are being supported. Was transport provided for people with mobility difficulties and other disabilities? Were isolated elderly contacted and helped to evacuate? Will undocumented migrants wish to seek life-saving shelter and aid given fears of deportation?

“The disaster is about people, especially people who cannot help themselves.

“Climate change might have intensified the hurricane. Climate change did not cause the hurricane disaster. The disaster is about where we construct our buildings and how, what preparation we can do for storms, and how society chooses to support those without knowledge, resources, or opportunities to act on their own.

“The disaster is about us creating and continuing vulnerability, not about the specifics of a single storm.”

Declared interests

Ilan Kelman currently receives funding from UK and Norway research councils as well as a range of private sector, non-governmental, and international organisations to research, analyse, and reduce vulnerability to disasters. He co-directs the NGO Risk RED (Risk Reduction Education for Disasters).