Free Forty Signs of Rain by Kim Stanley Robinson Page A

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.”

W
ater 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?

 
    F RANK 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,