T.ocean circulation that keeps our central northern corner of Europe warm (ish) is often likened to a large conveyor belt that delivers warm, equatorial warm water north at the surface, balanced by cold south-flowing at great depths . The Atlantic Meridional Overturning Circuit, or AMOC for short, delivers heat energy north at the same rate of 10 Hiroshima bombs all second and keeps our weather mild, and just a little too wet, and is vital to the climate in general.
New research has provided an important long-term context for scientists’ views on these Atlantic currents that provide warmth and climate stability to our coasts, with a major impact on the future. Changes in the AMOC in the geological past have caused major local and global impacts, and for several decades now geographers have been monitoring its strength.
Computer modeling and theory predict a steady decrease in the strength of the AMOC and its heat delivery service in response to human-induced changes in rainfall, flowing river water and the melting of Arctic sea ice and Greenland ice sheet. In addition, they show that the AMOC is one of the “tipping points” of global climate. If it is reduced beyond a certain limit, which is uncertain at this time, it can fall suddenly, with a major impact on our lives. Our best observation estimates, based on group data dating back to 1871, show that there has already been an estimated 15% decrease in AMOC strength.
What is needed, however, is a long – term context: is the current recession part of a long natural cycle, or is it due to human influence?
Research published in the journal Nature Geoscience this week has provided this context. Authors from Ireland, Germany and the UK have shown that the AMOC is the weakest it has ever been in over 1,000 years. They have done this using a combination of 11 different “proof measures” that indirectly find the strength of AMOC. These proxies include a combination of marine sediment, tree rings, ice heart chemistry and other exotic measurements that make up the bread and butter of the niche field within a niche of paleoceanography.
On their own, one such record should be carefully interpreted, but nine of these 11 proxies show a decrease in AMOC strength since the late 1800s, with an even greater weakening since the 1960s. Importantly, they also show that around 1850, the beginning of the impact of human industry, the strength of AMOC was relatively stable just back to before 400 AD.
This provides crucial speculative evidence linking human impact to the decline in AMOC strength, supporting what climate models have been showing for decades. These same models also predict that, under normal emission rates, the AMOC can be reduced to less than half its original strength by the year 2100. There is still a lot of uncertainty here, but the strong message: AMOC’s ongoing driving greenhouse gas emissions will be lower and lower. Fortunately, the recent Special Report on the Seas and the Cryosphere from the Intergovernmental Panel on Climate Change concluded that we were still “very unlikely” to come across the point of tension in this century. , but that doesn’t mean results aren’t closer to a term.
Reduced AMOCs are expected to bring overall colder weather to the UK and northern Europe, with far more severe winters and storms off the Atlantic, as well as less summer rainfall and crop productivity. and greater likelihood of real weather events such as the European 2015 summer heatwave. The impacts are not limited to this side of the Atlantic either. Sea levels are expected to rise on the east coast of the US, with increased flood risks and more severe hurricanes.
Such major changes in marine circulation also affect the ecosystems and aquaculture on which we depend. Marine deoxygenation and changes in key species abundance have been linked to an AMOC slowdown, along with an overall decline in Atlantic ocean productivity.
The southern end of the AMOC around Antarctica is also a cause for concern. The global ocean as a whole has absorbed more than 90% of human warming, completely undermining the changes in air temperature that we are all so concerned about. The great ocean hitting Antarctica is where most of this extra heat (and carbon dioxide) has been absorbed into the deep ocean, and it warms and acidifies at scary level. One of the key areas of research for seafarers like myself is whether the ocean continued to sweep human influences under the rug – and what could happen if that stopped.
This should not be a cause for despair and inaction. The same models that predict AMOC slowdown also show that a strong reduction in emissions can now drive AMOC recovery near the end of the century. Research could reduce uncertainty, but the message is clear: strong climate action is now needed at government and business levels, and it is incumbent on the people to drive such action with it. their wallets and votes.
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Andrew Meijers is a corporate marine expert at the British Antarctic Survey. He is deputy science director on the Polar Oceans team and leads the Orchestra’s research program examining marine circulation and its impact on climate.