For homo sapiens, a dry-land species, discussions of the climate and how it is changing tend to revolve around what is going on in the atmosphere. This is a dangerously parochial attitude, for the atmosphere is but one of two fluid systems circulating above Earth’s solid surface. The other, the ocean, is in many ways the more important of the pair.

It is the circulation of the ocean which, by redistributing heat, limits the temperature difference between tropics and poles to about 30°C. Were the atmosphere alone responsible for moving heat, that difference would be more like 110°C. And, when it comes to anthropogenic global warming, the problem would be far greater without the ocean’s buffering effect.

Not only does the ocean absorb heat which would otherwise remain in the air, it also swallows a third of the carbon dioxide emitted by human activity. Though that makes seawater more acid (or, strictly speaking, less alkaline), which may harm some marine species, much of the CO2 involved ends up in the abyss, where it can cause no greenhouse effect, and where it is likely to remain for many centuries.

The poverty of human understanding of ocean circulation, compared with that of the atmosphere, is therefore lamentable. And the aaas meeting was treated to an excellent lamentation on the matter by Susan Lozier of the Georgia Institute of Technology, who was also last year’s president of the American Geophysical Union.

Oceanographers worked out in the second half of the 20th century that the system’s engine room is in the North Atlantic. Here, in a process called the Atlantic meridional overturning circulation (amoc), water moving up from the tropics cools, thus increasing in density, until it becomes so heavy that it starts to sink, pulling more water up from farther south to replace it. Having descended as much as 3km, it then heads south itself.

Though some oceanic overturning of this sort goes on elsewhere, 90% of it happens in the North Atlantic. And it is this North Atlantic overturning which drives what is often described as a planet-spanning conveyor belt of connected currents.

That, at least, is conventional thinking. But Dr Lozier reckons it a bad analogy. A conveyor belt conveys an image of smooth and linear progress. This belt, though, jerks around all over the place, making it far harder to discover what is going on.

A smoothly moving belt need be examined only occasionally to check if its rate of progress is varying. So when, in 2005, a paper in Nature reported, on the basis of the five pertinent shipborne surveys which had been made since 1957, a 30% drop in the volume of amoc between 1992 and 2004, there was serious concern. If such a fall continued, it would change weather patterns, particularly in Europe, by altering planetary heat distribution. It would also reduce the rate at which CO2 was carried into the deep ocean.

As it happened, though, 2004 was a turning-point in observations of what is going on, for it saw the beginning of the deployment of a set of recording instruments which are now known as rapid amoc. These monitor the Atlantic a couple of degrees north of the Tropic of Cancer, the part of the world where the surveys reported in the Nature paper had been conducted. rapid amoc was joined in 2014 by an arctic counterpart, osnap, the Overturning in the Subpolar North Atlantic Programme.

The upshot has been the discovery that the rate of overturning can vary, apparently at random, as much as six-fold during the course of a year. The fall described in the Nature paper was an artefact of an impoverished data set.

Another finding of osnap has been that the details of where overturning happens in the North Atlantic are not as models had predicted. Most turnover, it turns out, occurs on the east side of the ocean, not the west, as previously believed. Though this may not matter much in the grand scheme of climate change, it is a further example of how poorly people have understood what is going on at sea.

The next step for osnap is to extend its remit into looking at carbon dioxide uptake. And more systematic studies are getting going in other parts of the ocean, too, as landlubbing humans are, at last, taking proper notice of the hitherto-neglected 71% of the surface of the planet they are pleased to call “Earth”, but which might, in truth, be better dubbed “Sea”. ■

Kevin McCarthy, the Republican speaker of the House of Representatives, said that a deal to raise America’s debt ceiling was “possible” by the end of the week. On Tuesday he met President Joe Biden and demanded spending cuts in exchange for increasing the government’s borrowing cap. Janet Yellen, America’s treasury secretary, has repeatedly warned that the government could default on its debt as soon as June 1st. Mr Biden will shorten his upcoming trip to Asia for the G7 summit as negotiations continue, cancelling planned stops in Papua New Guinea and Australia.

Liz Truss became the first former British prime minister in decades to visit Taiwan, where she called for an “economic NATO” to take a tougher stance against China and urged Rishi Sunak, Britain’s current prime minister, to declare China a security threat. China’s embassy in London called the visit a “dangerous political stunt”.

The boss of OpenAI suggested empowering American regulators to licence and audit artificial-intelligence models. Testifying before Congress, Sam Altman, whose startup created ChatGPT, said that AI firms should be given “guidelines about what’s expected in terms of disclosure”. America has so far taken a more laissez-faire approach towards AI regulation than Britain or the EU.

Japan’s economy expanded by an annualised rate of 1.6% between January and March, the first time in three quarters it has grown. That was faster than economists’ predicted growth rate of 0.7%. Strong domestic demand helped offset declining exports, which fell for the first time in six quarters. Japanese stocks rose to a 33-year high on Wednesday.

UBS, a Swiss bank, reckons it got a multi-billion-dollar cash boost from its takeover of Credit Suisse, a former competitor. The combined firms’ “negative goodwill”—a type of accounting gain generated when companies buy a rival at below tangible book value—reached $34.8bn as of the end of 2022. But the merger will also increase UBS’s legal and regulatory costs, which could reach $4bn over 12 months.

Ukraine’s Supreme Court dismissed its chief justice, Vsevolod Kniaziev, after he was detained on corruption charges. Prosecutors allege that Mr Kniaziev took a $2.7m bribe from an oligarch, Konstiantyn Zhevago, in exchange for a favourable verdict. (Mr Zhevago denied wrongdoing.) Ukrainian authorities, keen to ensure continued Western support, have recently cracked down on government graft.

A French judge issued an international arrest warrant for the governor of Lebanon’s central bank as part of a probe into alleged theft of public funds. Riad Salameh had failed to appear at a hearing in Paris. He, along with his brother and assistant, are under investigation in five European countries and Lebanon. He denies the accusations.

Fact of the day: 45%, the G7 members’ share of global GDP in 2021, down from around 70% in the late 1980s. Read the full story.