With Tropical Storm Theta a step away from the Canary Islands, an excellent context has been created for reflection on the changes that are being observed in the Atlantic, most likely linked to global warming. In the last fall it is almost becoming routine to talk about hurricanes or tropical storms approaching our country. This should not remove an iota of strangeness from the weather scenario. When the 21st century began, nobody could think that this would happen with such cadence, but soon the conception began to change, as soon as Hurricane Vince appeared in our lives.
Vince was a small but extraordinary tropical cyclone, which became a category 1 hurricane days before hitting the Gulf of Cádiz, where it already arrived as a tropical storm. The indictment was tiny, but it seemed to open the ‘box of thunder’. A month and a half later another system with similar characteristics affected the Canary Islands. That one, baptized as Delta, was much more virulent, with a hurricane wind that in the Tenerife observatory of Izaña left a maximum gust of 248 kilometers per hour. A Fuerteventura neighbor died and the damages were multimillion-dollar. In 2018 Leslie tore apart the central regions of Portugal, the same ones that flew over the tropical depression Alpha in September, fortunately with less ‘punch’.
In the last decade, tropical cyclones have been getting closer and closer to the European continent. It remains to be seen whether this is a temporary rebound or will be a constant in a warmer world. It is also not known if there are precedents for a similar increase in the past, because the reliable historical data on tropical cyclones in the North Atlantic begins in the year 1970, when satellite technology arrived. This makes it difficult to establish long-term trends.
It seems that the number does not increase, but the proximity does
There is no indication that the number of hurricanes or tropical storms in the Atlantic is increasing, nor that they will increase in the future. We continue to register around 90 hurricanes each year in the world and most of them appear in the Pacific Ocean, according to the latest Climate Science Special Report (CSSR for its acronym in English) of American authorship. The same experts, however, do see signs to forecast more adverse tropical cyclones in the future and perhaps close to Europe.
The oceans are absorbing almost all the excess energy contributed by global warming (93%) and this necessarily leads to the intensification of hurricanes. Since the 1970s, it is estimated that the world’s sea surface has warmed at the rate of 0.1 ° C per decade. With rising temperatures, the water vapor available in the troposphere is greater, providing additional fuel for storms.
The increase in temperatures in the most superficial layers of the sea is increasing the available humidity in the air, which is an additional fuel for tropical cyclones.
The authors of the CSSR also point out, a second consequence derived from this warming that also encourages tropical cyclones: the reduced availability of cold water in the layers immediately below the surface of the oceans. With the intense winds associated with hurricanes, this cooler mass used to emerge and became a kind of braking system. Now they are also heating up and eThis mechanism is losing effectiveness. It is true that not all the changes that are being observed are advantageous for these storms. They also observed that wind shear could increase in some regions of the western tropical Atlantic and that is always a drag on the development of tropical systems.
They move towards the poles between 53 and 62 kilometers per decade
A few years ago a study was published in Nature with a very suggestive title: ‘The Pole Migration of Maximum Intensity Tropical Cyclones‘. Scientists from the National Office for Oceanic and Atmospheric Administration (NOAA), also from the United States, concluded that tropical cyclones are moving towards the poles at rates of between 53 and 62 kilometers per decade.
The movement agrees with displacement that is also being observed in the tropics. In fact, the researchers warn of the almost unequivocal relationship between one thing and another. The latter is being observed especially in the Pacific, not so much in the Atlantic, although a small approach of tropical cyclones towards the poles has also been detected that contributes to the conclusion of the study.
The meteorologist Ángel Rivera, in his blog ‘En el tiempo’, has been warning of the growing trend towards the subtropicalization of our geographic environment. This observation links very well with what was argued by NOAA. According to Rivera, each time they could appear more cyclonic circulations of a subtropical character or subtropical jets, which would be the cause of an important part of the rains collected in the Peninsula, thus changing the regime observed in recent centuries. If all this is confirmed, a new risk planning should be started that takes into account the increased adversity in meteorological phenomena.