Prolonged rain and floods have damaged thousands of homes and businesses across the UK this January and February, with the cost being counted in hundreds of millions of pounds. How does this extreme weather link to climate change, the jet stream and the melting Arctic?
The Jet Stream
In 1883 the volcano at Mount Krakatoa erupted in the Sunda Strait between Java and Sumatra. The eruption was so powerful that the sky turned dark and ash caused vivid red sunsets around the world.
Meanwhile, wider effects of the eruption include records of a phenomenon that was labeled the “equatorial smoke stream”. These records constitute the first identification of jet streams, which were to be properly understood some years later, following the observations of pilots during World War II.
Jet streams are ribbon-like, fast flowing air currents, which move weather systems around the globe. The strongest jet streams are the polar jets, at 7–12 km above sea level, and the higher and somewhat weaker subtropical jets lie at around 10–16 km. They are caused by a combination of the world rotating on its axis and atmospheric temperature gradients and form at the boundaries between different climatic zones.
The northern polar jet flows from west to east, between the northern polar front and warmer air mass to the south. It’s the one we call the jet stream in our meteorological forecasts, affecting weather patterns across North America Europe and Asia.
Research into the effect of a warming arctic on extreme weather patterns set out to explore the hypothesis that if the Arctic is warming faster than other regions as a result of climate change, there will be progressive reduction of the temperature gradient between polar air and temperate conditions to the south, which will slow the jet stream and lead, in turn, to extreme and prolonged weather events across the northern and mid latitudes.
Since the 1980s, approximately 40% of permanent Arctic sea ice has been lost and an area of Arctic ice the size of Europe is now open water in summer.
This rapid warming is called Arctic Amplification and is intensified by the Albedo Effect, in which sunlight-reflecting ice and snow melt to reveal water, which absorbs the sun’s energy instead.
Professor Jennifer Francis of the Institute of Marine and Coastal Sciences at Rutgers University:
The jet stream really is the key part of the climate system that determines our weather. It creates it, and it steers it … The reason we believe things are starting to change is because the Arctic is warming much faster than areas farther south
The jet stream doesn’t always run in a straight line, but tends to curve north and south in giant loops called Rossby Waves that can stretch across hundreds of miles. If these waves are amplified by a weakening jet stream then the effect we are likely to see here in the UK and indeed across the northern hemisphere, are situations in which the weather tends to get stuck, leading to extreme conditions such as prolonged flooding or drought. It is a very credible explanation for recent extreme weather events, for example extreme flooding in the UK during January and February, and extreme drought in California.
Here in Britain, the economy may be growing but the ice is still melting, and if the theory of the jet stream is accurate, this is bringing climate change to our own doorstep. Which is why the economy can no longer be viewed in isolation. And this is the news.