Climate change could mean Scotland gets cooler, while the rest of the world gets warmer.
Arctic air has meant June has been a little cool so far but May was the warmest May ever recorded in Scotland in records which go back to 1884. High night-time temperatures pushed the average up so that it was 1.6ºC warmer than the previous warmest May in 2018 and it was 3.2°C warmer than the long-term average for May. We have data for more than 1,600 months and only February 1998 was farther above its monthly average. That long-term average is calculated from the years between 1991 and 2010. Compared to the first 20 years of the temperature record May 2024 was a stunning 4.3°C warmer than the 1884-1903 ‘normal.’ June 2023 was the warmest June ever recorded.
So far climate change has been about the world getting warmer and the extra energy in the atmosphere driving increasing flooding and stronger storms. There have also been regional changes, bringing more intense rain in some areas and drought in others.
Although Scotland has been regularly breaking weather records – 2022 was the warmest year ever and the ten warmest years in the 140-year record have all been since 1996 – we have actually been cushioned from more extreme variations by changes in ocean currents.
The public talk about the Gulf Stream feeding warm water to the west of Scotland, but the reality is a bit more complex. Scientists talk about the Atlantic Meridional Overturning Circulation (AMOC) which brings warm surface waters from the Tropics to the north-east Atlantic, which then sink when they meet the cold waters of the Arctic returning to the west and south as a cold, deep-water current. The heat energy contained in this flow is huge – about 50 times more than all the energy that human society uses.
Scotland is several degrees warmer than it would otherwise be because of this warm water circulation. If it switched off completely our climate would be more like that of Labrador in Canada, which is at the same latitude as Scotland.
We know that this current has been weakening since the 1930s, with an abrupt shift in the 1970s. This is why temperatures in Scotland and north-west Europe have not been rising quite as fast as in other parts of the world. We also know from ice core measurements that this current has completely and abruptly switched off for periods in the past.
A workshop this month looked at the science of abrupt changes to ocean circulation concluded that the risk of these kind of sudden, major changes has been underestimated in the past. A third of the best computer models predict major changes to the AMOC as soon as 2040.
One study shows a complete shutdown of the AMOC could see Scotland get more than 2ºC colder while most of the world is heading for 3ºC warmer than pre-industrial times. There would be major knock-on impacts on rainfall patterns around the world, creating droughts and reducing agricultural yields.
The threat of losing this ocean heat source means that Scotland is one of the most sensitive places in the world to climate change, and therefore has one of the greatest incentives to help lead the charge to reduce emissions.
A version of this article appeared in the Scotsman newspaper on the 19th June 2024.
Image: temperature change as a result of a complete switch off of the AMOC as a result of carbon in the atmosphere doubling. https://tos.org/oceanography/article/is-the-atlantic-overturning-circulation-approaching-a-tipping-point