“That would be an honor.”

“I don’t know if I’d go that far. But useful.”

“Useful, yes. Perhaps we could have you to dinner at our residence.”

“Thank you, that would be nice. But we have two small boys and we’ve lost all our baby-sitters, so to tell the truth it would be easier if you and some of your colleagues came to our place. In fact I’ve already talked to Charlie about this, and he’s looking forward to meeting you. We live in Bethesda, just across the border from the District. It’s not far.”

“Red Line.”

“Yes, very good. Red Line, Bethesda stop. I can give you directions from there.”

She got out her calendar, checked the coming weeks. Very full, as always. “How about a week from Friday? On a Friday we’ll be able to relax a little.”

“Thank you,” Drepung said, ducking his head. He and Rudra Cakrin had an exchange in Tibetan. “That would be very kind. And on the full moon too.”

“Is it? I’m afraid I don’t keep track.”

“We do. The tides, you see.”

Water flows through the oceans in steady recycling patterns, determined by the Coriolis force and the particular positions of the continents in our time. Surface currents can move in the opposite direction to bottom currents below them, and often do, forming systems like giant conveyor belts of water. The largest one is already famous, at least in part: the Gulf Stream is a segment of a warm surface current that flows north up the entire length of the Atlantic, all the way to Norway and Greenland. There the water cools and sinks, and begins a long journey south on the Atlantic Ocean floor, to the Cape of Good Hope and then east toward Australia, and even into the Pacific, where the water upwells and rejoins the surface flow, west to the Atlantic for the long haul north again. The round trip for any given water molecule takes about a thousand years.

Cooling salty water sinks more easily than cooling fresh water. Trade winds sweep clouds generated in the Gulf of Mexico west over Central America to dump their rain in the Pacific, leaving the remaining water in the Atlantic that much saltier. So the cooling water in the North Atlantic sinks well, aiding the power of the Gulf Stream. If the surface of the North Atlantic were to become rapidly fresher, it would not sink so well when it cooled, and that could stall the conveyor belt. The Gulf Stream would have nowhere to go, and would slow down, and sink farther south. Weather everywhere would change, becoming windier and drier in the Northern Hemisphere, and colder in places, especially in Europe.

The sudden desalination of the North Atlantic might seem an unlikely occurrence, but it has happened before. At the end of the last Ice Age, for instance, vast shallow lakes were created by the melting of the polar ice cap. Eventually these lakes broke through their ice dams and poured off into the oceans. The Canadian shield still sports the scars from three or four of these cataclysmic floods; one flowed down the Mississippi, one the Hudson, one the St. Lawrence.

These flows apparently stalled the world ocean conveyor belt current, and the climate of the whole world changed as a result, sometimes in as little as three years.

Now, would the Arctic sea ice, breaking into bergs and flowing south past Greenland, dump enough fresh water into the North Atlantic to stall the Gulf Stream again?

FRANK VANDERWAL kept track of climate news as a sort of morbid hobby. His friend Kenzo Hayakawa, an old climbing partner and grad school housemate, had spent time at NOAA before coming to NSF to work with the weather crowd on the ninth floor, and so Frank occasionally checked in with him to say hi and find out the latest. Things were getting wild out there; extreme weather events were touching down all over the world, the violent, short-term ones almost daily, the chronic problem situations piling one on the next, so that never were they entirely clear of one or another of them. The Hyperniño, severe drought in India and Peru, perpetual lightning fires in Malaysia; then on the daily scale, a typhoon destroying most of Mindanao, a snap freeze killing crops and breaking pipes all over Texas, and so on. Something every day.

Like a lot of climatologists and other weather people Frank had met, Kenzo presented all this news with a faintly proprietary air, as if he were curating the weather. He liked the wild stuff, and enjoyed sharing news of it, especially if it seemed to support his contention that the heat added anthropogenically to the atmosphere had been enough to change the Indian Ocean monsoon patterns for good, triggering global repercussions; this meant, in practice, almost everything that happened. This week for instance it was tornadoes, previously confined almost entirely to North America, as a kind of freak of that continent’s topography and latitude, but now appearing in East Africa and in Central Asia. Last week it had been the weakening of the Great World Ocean Current in the Indian Ocean rather than the Atlantic.

“Unbelievable,” Frank would say.

“I know. Isn’t it great?”

Before leaving for home at the end of the day, Frank often passed by another source of news, the little room filled with file cabinets and copy machines, informally called “The Department of Unfortunate Statistics.” Someone had started to tape on the beige walls of this room extra copies of pages that held interesting statistics or other bits of recent quantitative information. No one knew who had started the tradition, but now it was clearly a communal thing.

The oldest ones were headlines, things like:

WORLD BANK PRESIDENT SAYS FOUR BILLION LIVE ON LESS THAN TWO DOLLARS A DAY

or

AMERICA: FIVE PERCENT OF WORLD POPULATION, FIFTY PERCENT OF CORPORATE OWNERSHIP

Later pages were charts or tables of figures out of journal articles, or short articles of a quantitative nature out of the scientific literature.

When Frank went by on this day, Edgardo was in there at the coffee machine, as he so often was, looking at the latest. It was another headline:

352 RICHEST PEOPLE OWN AS MUCH AS THE POOREST TWO BILLION, SAYS CANADIAN FOOD PROJECT

“I don’t think this can be right,” Edgardo declared.

“How so?” Frank said.

“Because the poorest two billion have nothing, whereas the richest three hundred and fifty-two have a big percentage of the world’s total capital. I suspect it would take the poorest four billion at least to match the top three hundred and fifty.”

Anna came in as he was saying this, and wrinkled her nose as she went to the copying machine. She didn’t like this kind of conversation, Frank knew. It seemed to be a matter of distaste for belaboring the obvious. Or distrust in the data. Maybe she was the one who had taped up the brief quote: 72.8% of all statistics are made up on the spot.

Frank, wanting to bug her, said, “What do you think, Anna?”

“About what?”

Edgardo pointed to the headline and explained his objection.

Anna said, “I don’t know. Maybe if you add two billion small households up, it matches the richest three hundred.”

“Not this top three hundred. Have you seen the latest Forbes 500 reports?”

Anna shook her head impatiently, as if to say, Of course not, why would I waste my time? But Edgardo was an inveterate student of the stock market and the financial world in general. He tapped another taped-up page. “The average surplus value created by American workers is thirty-three dollars an hour.”

Anna said, “I wonder how they define surplus value.”

“Profit,” Frank said.

Edgardo shook his head. “You can cook the books and get rid of profit, but the surplus value, the value created beyond the pay for the labor, is still there.”