Controlling future summer weather conditions still within our reach

The continued burning of fossil fuels is likely to fuel even more extreme summers than 2018 due to its impact on the jet stream. The rapid disappearance of aerosols produced by pollution could, however, mitigate their effects until the middle of the century if countries like China phased out these fuels, according to an international team of climate scientists using climate models to predict changes in climate change. Occurrence of this near-resonant amplification events associated with persistent extreme weather conditions.

These extreme jet-stream paths cause floods, droughts and forest fires. By 2018, the summer weather included floods in Japan, record heat waves in North America, Europe and Asia, forest fires in Greece and even parts of the Arctic. The heat and drought in California led to the worst wildfire season ever recorded.

The jet stream and extreme weather events

QRA events produce extreme summer weather conditions when the jet stream has large north-south meanders and becomes stationary with peaks and valleys trapped in place.

"Most of the stationary jet stream disturbances will disappear over time," said Michael Mann, Distinguished Professor of Atmospheric Sciences and Director of the Earth System Science Center. "However, under certain circumstances, wave disturbance is effectively limited by an atmospheric waveguide, which is similar to how a coaxial cable drives a television signal, so disturbances can not be easily dissipated and very large amplitude in the north and south jet stream can stay in place as it revolves around the globe. "

"If the same weather persists for weeks in a given region, sunny days can turn into a severe heat wave and drought, as well as floods," said Stefan Rahmstorf, of the Institute for Research on the impact of the climate of Potsdam (PIK), Germany.

In the summer of 2018, the impacts of climate change on extreme weather conditions were no longer subtle, according to Mann.

"This has played in real time on our television screens and headlines in our newspapers in the form of floods, droughts, heat waves and extreme wildfires on the scale of the world. hemisphere, "added Mann.

The role of quasi-resonant amplification

Mann notes that the QRA phenomenon has played an important role in producing this series of unprecedented meteorological events in the hemisphere.

Previous work by Mann and his colleagues has shown a link between extreme weather events and climate-induced changes in the jet stream. Although researchers can not accurately identify quality risk assessment events in climate models, changes in temperature capture temperature changes very well.

"QRA events have been shown to have a well-defined signature in terms of temperature variation in the lower atmosphere in the lower atmosphere," said Mann. "The temperature change as a function of latitude and how it reacts to increasing greenhouse gas concentrations depends on a well-understood and well-represented physics of climate models."

The researchers found that the pattern of amplified Arctic warming – Arctic amplification – which slows the jet stream, also increases the frequency of QRA episodes.

The co-author of the study, Dim Coumou, who works at PIK and VU Amsterdam, said that we do not have enough confidence in climate models to predict this type of extreme weather because they are too coarse.

"However, the models are producing models of large-scale temperature change faithfully," added PIK co-author Kai Kornhuber.

The researchers report today (October 31) in Progress of science that amplified Arctic warming, called Arctic amplification, associated with man-made climate change is slowing the jet stream and increasing the frequency of QRA episodes.

They found that climate models, when they are used to project future changes in extreme weather behavior – because they are unable to capture the QRA phenomenon – probably underestimate how future climate change could lead to More persistent summer temperature extremes such as those in the summer of 2018. If carbon dioxide continues to be added to the atmosphere, the incidence of QRA and related extreme weather events would continue to increase at the same rate as in recent decades.

Effect of aerosol on temperature regulation

However, greenhouse gases are not the only consideration for the future of the Earth's climate. Although the United States and Europe have adopted "cleaner" coal burning methods that remove pollutants that produce aerosols from emissions, many other parts of the world have not yet done so. Aerosols are particles suspended in the air.

If these countries, by the middle of the century, opt for a cleaner coal combustion technology, the mid-latitude regions of the world will warm up and the amplification in the Arctic will decrease. This will happen because aerosols, especially in mid-latitudes where the sun is abundant, cool the Earth by reflecting the heat of the planet. Without these aerosols, this region of the Earth will warm up, mitigating any further increases in QRAs as the warming difference between the Arctic and mid-latitudes decreases.

However, by mid-century, once aerosols are no longer produced, warming of the greenhouse effect again dominates the climate. Limiting the burning of fossil fuels can prevent an increase in persistent summer temperature extremes, although the current occurrence rate of summers like 2018 probably persists. "The future is still in our hands when it comes to dangerous and damaging summer weather extremes." Said Mann. "It's just our willingness to move quickly from fossil fuels to renewable energies."

Explore further:
Extreme weather events linked to climate change have an impact on the jet stream

More information:
Mann E. et al., "Predicted changes in persistent summer weather extremes: the role of near-resonant amplification," Progress of science (2018). advance.sciencemag.org/content/4/10/eaat3272