If efforts to curb global warming, such as the Paris Agreement, fail to reverse the rise in temperatures, all climate models paint a very hot scenario for the second half of the century. The increase in the concentration of greenhouse gases (GHG), such as CO2, will cause the global average temperature to rise a minimum of two degrees, although at the upper end it could exceed three or four degrees. With these temperatures, one of the most affected climatic processes would be the great air currents (jet stream, in English) that animate the global climate.
One of those air currents was to blame for the record of January 8, 2015. The plane from New York took advantage of a strong and constant tail wind that literally blew it into the British capital. Unlike what happens with flat surfaces, in a sphere like the Earth the shortest distance between two points is not a straight line, but an arc over the great circle of the sphere. The optimal arc between Europe and North America has turned the northernmost parts of the Atlantic into the largest air corridor in the world. In this area the subtropical jet stream of the northern hemisphere blows, which does not affect the planes that go as well as those that come.
"The jet stream is the reason why transatlantic flights to the east last about an hour less than flights going west," says University of Reading (UK) meteorologist Paul Williams. In the absence of wind, a plane at optimal speed flying over the Atlantic great circle would take about 6 hours and 9 minutes to complete the London-New York route. But this current of air, moving through the upper layers of the atmosphere, blows from the west with winds of more than 300 kilometers per hour. It is not the same to have that tail gale as in front. "Climate change is accelerating the jet stream at the altitude that planes fly, which is making eastbound trips faster and westbound slower," explains Williams.
Simulations carried out by this scientist for a scenario in which the GHG concentration has doubled, which could happen before the end of the century, show that flights from North America will be shortened by about four minutes on average. Meanwhile, those from Europe will last 5 minutes and 18 seconds. So a round trip will be more than a minute longer, as published in Environmental Research Letters.
It doesn't seem like much to a single passenger, but accumulated can have a great impact. Only through the North Atlantic corridor more than 2,500 daily flights fly in one month of August, according to figures from the NATS air control center. If these figures are maintained, by 2050 and beyond, that will translate into several thousand more hours of flight, which means more fuel to burn. According to Civil Aviation, for every kilogram of fuel, 3.16 kg of CO2 are generated, which means that in the future flights, in addition to being longer, will be dirtier.
A report by the International Civil Aviation Organization published in August included several of the impacts that climate change could have on flights. In addition to affecting the duration of the same, optimizing the design and performance of the engines or forcing greater elasticity in the programming of routes, the heating will disrupt the development of the journeys itself in two particularly stressful moments for many travelers: the moment take-off and in-flight turbulence.
Although turbulence is common on flights, its intensity rarely forces an emergency landing. In Iberia, for example, they only have the case of one flight from Milan and another from Brazil, but both happened several years ago. However, this summer, a United Airlines flight from Houston (USA) to London had to land at an airport in Ireland due to turbulence. 12 people, including passengers and crew, were injured.
"Clear air turbulence is caused by instabilities in the jet stream. In fact, there is three times more turbulence in these air currents than in other parts of the atmosphere," recalls Williams. Together with his colleague from the University of East Anglia, Manoj Joshi, the British scientist conducted in 2013 one of the few studies on the connection between climate change and clear air turbulence, the least predictable of all. They then estimated that, especially in the winter months, episodes of turbulence could increase by up to 40% while its intensity could increase by 170%. "As climate change accelerates the jet stream, the instabilities will become more frequent and stronger," adds Williams.
In summer the problem will be another. In the heat, the air becomes less dense, making it difficult for the wings to support the aircraft at takeoff. For this reason, in July and August, at airports such as Barajas, in Madrid, the heaviest flights are scheduled for the coolest hours of the day and take off on the longest runway. Sometimes that is not enough and you have to lighten the plane by releasing ballast, either by reducing the amount of fuel, cargo or even passengers. The problem is also well known in airports such as those in Quito or Mexico City, at more than 2,000 meters, or La Paz, at 4,061 meters of altitude.
"The elevation of the airport has the same effect as the rise in temperatures, since at higher altitudes the density of the air is lower, so the planes have to go faster to take off. That, or reduce weight," says the researcher at Columbia University (USA) Ethan Coffel. Together with colleagues at NASA, Coffel studied how global warming would affect aircraft weight restrictions.
The researchers used the specifications of a Boeing 737 800 series, a short- and medium-range aircraft, for their calculations. They applied them to four US airports: one very hot in summer (Phoenix), another elevated (Denver, at 1,600 meters of altitude) and two with relatively short runways (Reagan airport in Washington and La Jolla in New York). As the century progresses, all four airports will have to increase takeoff weight restrictions and many flights will have to drop passengers on the ground.
Photo: Image of world air traffic created with observations from the PROBA-V satellite of the European Space Agency. ESA / DLR / SES