Could the UK actually get colder with global warming? 

Could the UK actually get colder with global warming?Just nowSimon King and Mark PoyntingBBC Weather and Climate teamsGetty ImagesOf all the possible climate futures, there’s a scenario where the United Kingdom and north-west Europe buck the trend of global warming and instead face plunging temperatures and freezing winters.It’s not the most likely outcome, but a number of scientists fear that the chance of it happening is growing, and that the consequences would be so great that it deserves proper consideration.They are concerned that the ocean currents that bring warm water from the tropics to the North Atlantic could weaken – or even collapse – in response to climate change.Huge uncertainties remain about when – or even whether – a collapse could happen. So, how likely is it, and what would it mean?The system of Atlantic currents, called the Atlantic Meridional Overturning Circulation (Amoc), is a key reason why the UK is warmer than Moscow, despite being a similar distance from the Equator.Forming a vital part of our climate system, this conveyor belt distributes energy around the planet, bringing warm, salty water from the tropical Atlantic to cooler regions south of Greenland and Iceland, and also the Nordic Seas.The warmth from the ocean is transferred to the air above it, helping keep temperatures milder than they otherwise would be.As this salty water cools, it becomes denser, and sinks, before flowing back towards the southern hemisphere as a deep ocean current. This water eventually gets pulled back up to the surface, and the circulation continues.But Amoc appears to be getting weaker.We don’t know for sure, because direct and continuous measurements of Amoc strength have only been taken since 2004. That’s not long enough to be able to identify a definite change.But indirect evidence suggests it could have already slowed by around 15% over the last couple of centuries, although not all scientists agree.One indication is the sediments on the ocean floor. Larger grains indicate a stronger current. By measuring the size of the grains and calculating their age, scientists can estimate how much Amoc has slowed over time.Another piece of evidence is the so-called ‘cold blob’ or ‘warming hole’ in the north Atlantic. This describes a region which appears to have cooled in recent decades, unlike the vast majority of the world.A slowdown in Amoc – meaning less warmer water would be transported to this region – is seen as a possible culprit.This is “a very clear signature and footprint of a classic Amoc slowdown” says Matthew England, professor of oceanography at the University of South Wales.The UN’s Intergovernmental Panel on Climate Change (IPCC) expects Amoc to weaken this century. But the major concern is that Amoc could suddenly “switch off”, as appears to have happened repeatedly in the Earth’s past.Today, global warming appears to be making the water in the north Atlantic less salty, due to extra freshwater from a melting Greenland ice sh