When listing the causes of the devastating Hurricane Harvey, climate change is far from first.
However, there are some signs that suggest that global warming has not been done without.
Hurricanes are a complex natural phenomenon that is extremely difficult to predict, regardless of whether the global temperature rises or not.
Photo: Houston after storm Harvey
It is also extremely difficult to single out with scientific certainty the effect of climatic changes on the strength of hurricanes, because they happen relatively rarely, their frequency varies from year to year, and scientists simply do not have enough data for comparative analysis.
There are, however, facts about which we can speak more or less confidently.
There is a well-known physical law, it is called the Clapeyron-Clausius equation: according to it, an atmosphere with a higher temperature contains more moisture.
When the air temperature rises by one degree Celsius, the humidity rises by 7%. As a result, it rains more intensively in warm air.
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Another element that we can talk about with some certainty is sea temperature.
“The water temperature in the Gulf of Mexico is now about 1.5 degrees higher than the average between 1980 and 2010,” Brian Hoskins of the Climate Change Institute at the London School of Economics told the BBC.
“This is very important because it creates the conditions for a more powerful storm, and the fact that global warming has an effect on the warming of the water in the Gulf of Mexico is, in general, almost inevitable,” he says.
Many scientists have little doubt about the link between the intensity of precipitation, which continues to fall in the Houston area, with the ongoing climate changes.
“This is the kind of phenomenon - in the sense of more intense rainfall - that is to be expected in warmer climates,” says Dr. Fridericke Otto of Oxford University. "Looking at the intensity of rainfall [in the Houston area], it's reasonable to assume that climate change played a role."
ANALYSIS: The Billion Dollar Question
Roger Harrabin, environmental analyst
Environmental lawyers are now vigorously debating whether phenomena such as Hurricane Harvey should be considered acts of nature outside of human control - the so-called "hand of the Most High", or is it compounded by human activities, namely the burning of fossil fuels …
In an article published by them in the commentary section of the journal Nature Geoscience, an article says that countries that do not take part in global efforts to limit such emissions to the atmosphere may be sued.
Until now, however, attempts to bring someone to justice for natural phenomena have ended, as a rule, in vain.
But lawyers at Client Earth in London and Earth and Water Law in Washington believe things could soon change.
A new discipline known as attribution science, they said, will allow courts to determine with sufficient accuracy that specific events have occurred or have been aggravated by human-induced climate change.
They also believe that in the future, governments or businesses will be successfully prosecuted if they fail to reduce greenhouse gas emissions.
However, the question remains open why the storm in Texas was so long. Indeed, because of this duration, many areas were flooded.
Some researchers are inclined to see the consequences of climate change here too.
Professor Stefan Ramstorf of the Potsdam Institute for the Study of Climate Change says that the reason for the overall slowdown in air circulation in the atmosphere in mid-latitudes may be climate change in other regions of the Earth.
“This is the result of disproportionate warming in the Arctic, which causes weather systems to become less mobile and stay in the same region longer. This, in turn, can exacerbate phenomena similar to those seen in Houston,”he says.
However, it must be said that similar "sedentary" storms were noted more than once in Texas and in the past.
Tropical storms "Claudet" in 1979 and "Allison" in 2001 did not leave the place for a long period and were accompanied by powerful downpours. Accordingly, some scientists believe that linking the slowly moving Harvey with climate change is overkill.
“I don’t think it’s worth speculating on the relationship between complex and understudied processes, such as warming in the Arctic, and current events, until more thorough research is done,” says Dr. Fridericke Otto.
Experts believe that when talking about events like Hurricane Harvey, one should keep in mind not only the rise in temperature - both air and sea water - but also changes in the circulation of air in the atmosphere.
Sometimes changes in temperature and air circulation cancel each other out. Sometimes they reinforce mutual change. It will take a lot of effort and expense to fully understand how this mechanism works.
“When we talk about hurricanes, we need to understand how they can develop in the real world, and how they could develop in a world where the climate does not change,” says Dr. Otto. "But repeating high-resolution simulations over and over again is extremely expensive."
Meanwhile, other researchers say that we all look at this problem in the wrong way.
Regardless of whether human activities affect the Earth's climate, thereby exacerbating Hurricane Harvey, they believe that humanity's contribution to this particular disaster can be easily and simply explained.
“A hurricane is just a storm, not a catastrophe,” says Dr. Ilan Kelman of the Institute for Risk and Disaster Reduction at the Institute for Global Health at University College London.
“The disaster is that the population of Houston has increased by 40% since 1990. The disaster is that too many people in the city are too poor to afford insurance,”he says.
“It’s not climate change that makes people build houses near the coastline, which is hit by storms,” says the scientist. "And the fact that a natural phenomenon is turning into a disaster is the result of our own choice, which has nothing to do with climate change."
Matt McGrath