
It's called the Atlantic Meridional Overturning Circulation, or AMOC. It's part of a worldwide system of ocean currents distributing heat around the planet
Because the equator receives a lot more solar energy than the polar regions, heat builds up in the tropics. There is a principle in physics called thermodynamic equilibrium, which essentially means everything wants to be the same temperature as everything else. It's why your hot coffee cools off, because the heat energy in it is distributed to the surrounding air so that eventually the coffee and the air are the same temperature, have the same level of heat energy. That is true of the world just as it is for your coffee.
So the differing levels of heat energy in different parts of the ocean create currents that constantly carry warmer and cooler water in a conveyor belt of currents across and around the oceans. The warmer currents are in red, the cooler ones in blue. Warm water is less dense than cold water, so the warm currents are shallow ones, hear the surface of the water, while the dense, cooler, currents are deep ones - which is why the current can cross paths without interacting.
The point is, this system of currents has a major influence on both the long-term of climate and the short-term weather. It affects the wind patterns and how storms form - why for example, hurricanes often form more towards Africa and move westward across the Atlantic.
That warm current also explains why south and southwest England have mild enough weather that winter snow is rare in London and you can find palm trees in Torquay even though London is at about the same latitude as the mouth of the St. Lawrence River between Newfoundland and Labrador.
Why do I bring all of this up? To see why, let's look more locally. Because this is a entire belt of currents, we could start at any point, but for what is relevant to us at the moment we'll start in the Caribbean, with warm water being brought along the southeast US coast before cutting across the Atlantic to Great Britain and then heading for Greenland.
As the water reaches the area around Greenland, it has cooled enough - become dense enough - to sink to deeper water, with that deep current propelled by the force of the water sinking behind it.
What keeps this system going is that the tropics continue to get more solar energy than the polar regions, so that differential in heat driving the system still exists. Also, water in polar regions is saltier than that in the tropics because ice is essentially fresh water, so the amount of it locked up in ice can't contain any of the salt. Saltier water is denser than fresher water, and that difference in density also helps propel the system. The relevance of all that will become obvious in a moment or two.
The news here is that a new study published in the peer-reviewed journal Nature Geoscience reports that this current is now moving more slowly than it has in at least 1,600 years and the belief is that this is directly related to climate change.

Those effects can be so wide-ranging - North America to Europe to northern Africa - because, as years of research have made clear, the Atlantic portion of the world conveyor belt - the AMOC - is the engine that drives it, moving water at 100 times the flow of the Amazon river.
But that circulation has slowed down by at least 15% since 1950, something the new study calls "unprecedented in the past millennium." The specific suspected culprit is melting Arctic ice and the reduced salinity of polar oceans that results. The effects on weather patterns can already be detected.
The deeper concern is that if warming is not halted, the circulation may slow by 34% to 45% by the end of the century, by which time we may have already passed the tipping point, the point beyond which even if all warming was stopped entirely, it would be too late to prevent the circulation from slowing to a stop with catastrophic impacts.
Here it's necessary to note that, no, this is not the movie The Day After Tomorrow, the impacts would not be instantaneous, but over years and decades, yes, they would be devastating.

This does not mean things are hopeless.
For one thing, a new report from Ember, a London-based environment think tank, found that in 2020, for the first time, the 27 countries of the European Union generated more electricity with renewables - wind, solar, and hydro - than with fossil fuels, continuing a shifting pattern developing over the past 10 years.
What's more, a study from late 2018 found that at that point, generating utility-level electricity through solar and wind was already cheaper than coal and new natural gas plants - without subsidies or a price on carbon.
The study from the financial firm Lazard Ltd. applied a Levelized Cost of Energy, or LCOE, analysis, which looks at the cost of power from a plant averaged over its entire lifetime. It found - over two years ago - that the cost of renewables had dropped so much that in many areas, building and running new renewables was already cheaper than just continuing to run existing coal and nuclear plants.
In other words, the economics are clearly in favor of a clean energy future.
Then there is the fact that according to the Peoples' Climate Vote, the largest survey of public opinion on climate change and policy solutions ever conducted, nearly 2/3 of people around the world, including 65% of those in the US, think it's a global emergency that warrants a serious response.
Survey data was gathered from 1.2 million respondents in 50 high-, middle-, and low-income countries covering 56% of the world's population. People between the ages of 14 and 18 expressed the greatest level of concern, with nearly 70% saying there is a climate emergency, but even 58% of those aged 60 and over agreed.
And then there is President Joe Blahden, who whatever his faults is more concerned about climate change than any previous president.
On his first day in office he canceled the permit for the Keystone XL pipeline, the one intended to carry highly-polluting tar sands from Alberta to Texas. He has rejoined the Paris Accords, issued an executive order suspending new oil and gas leases on public lands, directed federal agencies to purchase electric cars by the thousands, and urged Congress to end some fossil-fuel subsidies.
And he has proposed to eliminate net greenhouse gas emissions from power plants by 2035 while proposing to invest $2 trillion over four years to transform to a clean energy economy. I'll note in passing that much of this would not have happened were it not for Bernie Sanders representatives on that unity task force, but the important thing here is that it happened.
And it's certainly doable, considering that the National Academies of Sciences, Engineering, and Medicine has released a draft version of a report which argues that $2 trillion over 10 years would be enough to build an economy that is not only net-zero but would "also build a more competitive economy, increase high-quality jobs, and help address social injustice in the energy system."
Meanwhile, earlier this month the latest version of the federal CLEAN Future Act was introduced in the House of Representatives, an event greeted with applause by environmental groups such as Earthjustice and the NRDC.
This latest version aims to achieve US carbon neutrality by 2050 with an interim goal of reducing pollution by 50% from 2005 levels by 2030.
It all sounds so good, even allowing for the inevitable political hurdles and opposition from fat cats, corporations, and corporate-funded interests. It still sounds so good and so hopeful.
And it is, it is - as far as it goes.
Which is the problem: It doesn't go far enough.
For one thing, Blahden's order to suspend new oil and gas leases didn't prevent 31 new leases from being issued during his in 1st month in office.
For another, praise for the CLEAN Future Act was hardly universal. Groups like Friends of the Earth and Food & Water Watch said the legislation is fundamentally and dangerously lacking.
My own objection is that the bill treats fracking as a clean energy. But fracking is designed to increase production of natural gas. The whole point of it is not to move away from fossil fuels but to enable us to continue to rely on them. A climate program that embraces fracking is not serious. As Lukas Ross, program manager at Friends of the Earth put it, "A clean energy standard that qualifies fracked gas is a joke."
Meanwhile, Mitch Jones, policy director at Food & Water Watch, called the bill "a Green New Dud" because "it fails to grasp the fundamental truth of fighting climate change: We must stop extracting and burning fossil fuels as soon as possible. We should not waste time creating credit schemes and offsets markets, or prop up fossil fuels with carbon capture fantasies."
And we shouldn't. When I was preparing this piece, I kept thinking "if this was a war." But that's silly, because this is a war. A war we are waging on ourselves, on the climate, a war we are waging on the life networks and patterns of this planet and our collective future.
On January 27, Nature published a report saying that an analysis of ocean surface temperatures shows that the planet is hotter now than at any time in the preceding 12,000 years, and that it may actually be warmer than at any point during the last 125,000 years.
Each of the past four decades has been hotter than the one before. 2020 tied for the hottest year on record and the past seven years have been the seven hottest.

No "natural cycle" or other BS is going to explain any of that that away.
It's not enough. Even the grand-sounding promises and solemnly-intoned pledges at international conferences are not enough.
According to new findings published in December by the United Nations Environment Program, if nations are to meet a central goal of the Paris agreement of holding the Earth's warming to “well below” 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels, they will have to “roughly triple” their current emissions-cutting pledges. If they are to keep heating below 1.5 degrees Celsius (2.7 degrees Fahrenheit), they would need to increase their targets at least fivefold - to make five times the cuts they are pledging.
And despite all the pledges, global greenhouse gas emissions, on average, have risen about 1.4 percent annually over the past decade. The world remains on a trajectory to see the temperature increase about 3 degrees Celsius (5.4 degrees Fahrenheit) this century - a level that climatologists say would be catastrophic.
What we're doing - collectively - is simply not enough. And I mean the world, particularly the industrialized world, at large, not just the US. But if I've seemed a times to concentrate on the US, that's because I have. First off because it's us, it's the one we have the most control over. And we are the world's second largest producer of greenhouse gases and we have one of the if not the most carbon-intensive lifestyle. The carbon footprint of the average American is about 17.6 tons of carbon dioxide equivalents a year, about double the footprint of a person living in the EU or the UK, and almost 10 times that of the average citizen of India.
So yes, the world needs to do more and particularly we here need to do more and dammit yes, it will affect your lifestyle, yes, you might have to do without a few hi-tech goodies, yes, you might have to live with a little less convenience, you might have to take the train instead of flying everywhere, you might have to ride the bus to work instead of driving, you might have to make a lot of changes, some of them more significant than others.
But I'm going to ask you to think back a few decades - if you're as old as me, think back to the '60s. I want you to think back and ask yourself, I've asked this before but I'm asking it again and I want you to think seriously about it. I'm not considering how issues of poverty or bigotry or physical limitations might have affected you personally for this, just consider how the average, the typical, American lived then, the level of technology, the level of convenience, available at that time. And ask yourself: Was that way of living so terrible that you would sacrifice a world for yourself and your children rather than live that way again.
Because right now, yes, we are engaged in a war. And the problem is, we're winning.
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