Heatwaves caused by fall in air pollution
The effect of air pollution on global temperatures has been well understood for a long time, as evidenced by the estimated 0.5C fall in the aftermath of the Pinatubo eruption in 1991. The Telegraph covers the story:
Met Office and Spanish researchers conclude cleaner skies since the 1980s allow more of the Sun’s heat to reach Earth’s surface.
Britain’s scorching heatwaves are being driven by cleaner skies after pollution was stripped from the atmosphere, new research suggests.
Temperatures in Europe have warmed twice as much as the rest of the world since the 1980s, figures show, with the continent now 2.3C warmer than it was in the pre-industrial era. In the same period, the global average is 1.3C.
The steep temperature rise in western Europe has outstripped expectations and has left experts puzzled as to its cause and concerned about the increase in deadly heatwaves.
Now Spanish researchers and the Met Office have concluded that most of the extra heat experienced in Britain and Europe is linked to the fall in particle emissions in recent decades.
The signing of the Montreal Protocol in 1987, which was championed by Margaret Thatcher, was designed to protect the Earth’s ozone layer and led to a general reduction in aerosols and particulates being emitted into the atmosphere.
Scientists now believe the reduction in some pollutants allows more of the Sun’s heat to reach the Earth’s surface and also changes how air circulates globally to increase the chance of prolonged hot weather in Europe.
Prof Markus Donat, of the Barcelona Supercomputing Centre, said: “On the one hand, the cleaner air lets more sunlight reach the surface.
“On the other hand, we think that this additional energy causes atmospheric circulation changes that bring even more heat to Western Europe.”
Aerosols, particularly sulphates, reflect sunlight back into space which cools the planet. But when they are absent the Earth absorbs more heat, particularly at the poles, and shrinks the temperature difference between the poles and the equator.
A significant difference between the temperature at the poles and the tropics is crucial for keeping the jet stream moving.
The jet stream, the fast current of wind high in the sky that controls the weather, blows from west to east and flows in giant curves around the world in what are known as Rossby waves, which are caused by the planet’s rotation.
Normally these waves undulate constantly, but the smaller temperature contrast created partly by the lack of sulphates in the air is causing them almost to stall, locking in weather patterns and leaving Europe trapped under sweltering heat domes and high temperatures.
The new research was published in the journal Geophysical Research Letters.
The full story is here.