Weather we like it or not

At our February meeting we had a very interesting talk by Gina, who is our Climate Ambassador, on the weather and climate change. Her talk is included in this month’s Buzz (our newsletter), and I am including it here also as it provides a clear analysis of the weather over the last 4 years, the jet stream, and climate change. Thanks Gina for drawing all this information together for us.

Kate

Recent UK weather

It will not have passed unnoticed that we are just coming out of the Beast from the East 2. We were in fact in the grip of an unusually cold period of weather thanks to a flow of cold easterly winds from Siberia. On the morning of February 11, the village of Braemar in the Scottish Highlands recorded -23.0°C, the UK’s coldest temperature since 1995 and coldest February temperature since the 1950s. The two cold spells of 2018 and 2021 bookend a volatile four years of winter weather. In February 2019, the UK experienced a “winter heatwave” when the temperature reached 21.2°C at Kew Gardens in London. The following year saw the country’s wettest February on record stretching back to 1862, with winter storms Ciara and Dennis producing some of the rainiest individual days on record. Extreme cold, a heatwave, a deluge, and another cold snap: the succession of different extremes raises questions about climate variability and climate change.

Atlantic Jet Stream

Western Europe is at the mercy of the Atlantic jet stream – a band of westerly winds which steer powerful weather systems, flanked by cold air to its north and warmer air to its south. The jet stream is extremely variable and fluctuations in its strength and position are the main reason why the region can have such varied weather.

In both 2021 and 2018, the jet stream was unusually weak and shifted southward, allowing cold air to flood out of the Arctic. In early 2020, the jet stream was supercharged, keeping colder air locked up and instead pushing in mild, moisture-laden air and storm systems from the Atlantic. In 2019, it buckled northwards, allowing a dome of high pressure to develop over the UK under which the temperature skyrocketed. These different patterns all fall within natural climate variability. The weakened jet stream in 2018 and this year, as well as the strengthened jet stream in 2020, are all linked to variability in the Arctic stratospheric polar vortex – effectively a vast low-pressure system around 30km above the surface, which fluctuates in strength from year to year.

Climate change

But we do know that climate change is likely to make winters milder and wetter in the UK, largely because warmer air can hold much more water. This is supported by recent observations: the winters of 2013-14, 2015-16 and 2019-20 all rank in the top five wettest on record. Recent research has shown that climate change has also made exceptionally warm winter days – such as the 20°C heatwave in February 2019 – around 300 times more likely, although they remain rare because the specific atmospheric configuration required is so unlikely.

So there is evidence to support climate change having amplified the extreme heat of 2019 and the rain of 2020. But what about cold weather and climate change? It is important to remember that extremely cold weather can still happen in a warming climate. If climate change is like loading a die, then rolling a one is still possible. Just because you roll a one every so often does not tell you that the die is not loaded. For that, you need to look at longer periods of time, to see if you are rolling more sixes and fewer ones.

The Central England Temperature (CET) is the world’s longest-running continuous instrumental temperature record, with data from 1659. It gives a clear indication of how even the coldest winters in recent times pale in comparison with those of the past. 

A winter with an average temperature below 2°C used to occur about once per decade. Central England has not had a winter that cold since 1978-79 – a never-before-observed gap of four consecutive decades and counting. Despite plenty of cold spells in the past few decades, no one under the age of 42 has lived through what could be considered a historically cold winter season in central England.

The evidence for manmade climate change is overwhelming and global warming may be speeding up. The 20 warmest years on record have all come since 1995. And just as the rate of temperature rise looks to be accelerating, so too does one of its main consequences: the rise in sea level. Over the last 20 years sea levels have risen at roughly twice the speed of the preceding 80 years.  

So how will this affect us?

  • The higher latitudes, where the UK sits, will be hotter and wetter.
  • In Britain we will have hotter summers. By 2040, we expect more than half of our summers to exceed 2003 temperatures and we will have wetter winters, and extreme rainfall events will become even more extreme. 
  • Sea levels will rise significantly, perhaps by up to a metre in places by 2100 and we will experience frequent and more extreme flooding and coastal erosion, caused by those wetter winters, heavier rain, stronger storms and rising sea levels. 
  • More water shortages and higher drought risk, caused by the hotter drier summers and less predictable rainfall. 
  • More air and water pollution, due to those longer, hotter summers. 
  • More damage to wildlife and the habitat on which it depends. In many cases that damage may be existential. If we continue to emit greenhouse gases at the same rate as today, then by 2050 one million species across the globe are likely to vanish. And as many of you will know we are seeing many species currently endangered in the UK including Atlantic salmon and cod who cannot survive increasing sea temperatures, kittiwakes and guillemots failing due to declining sand eel populations, bees (there are 250 different types) at risk because of intensive farming and loss of habitat and puffins in decline because of over fishing. 

Friends of the Earth suggest that governments should be pressed to work on the following six areas – sustainable transport, power generation, buildings and homes, trees and food, consumption and international justice.

And finally one mildly interesting factoid and an app that is quite useful. 

  • Standard Sea Level pressure is 1013 millibars (I think they call in Hecto Pascals now). For every one millibar below this, the sea level rises by 1cm and conversely for every millibar above, the sea level is depressed. In the great storm of 1987, the lowest pressure recorded was 953 mb, so the sea level would have been 0.6m higher than normal. 
  • Energy Watch GB or NG ESO are both (free) apps that allow you to see at any time the way in which our electricity is being generated and therefore the percentage that is zero carbon.

Gina

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