A brief, large flood of fresh water might nudge us toward an abrupt cooling even if the dilution were insignificant when averaged over time. We have to discover what has made the climate of the past 8, 000 years relatively stable, and then figure out how to prop it up. Fatalism, in other words, might well be foolish. Meaning of three sheets to the wind. Pollen cores are still a primary means of seeing what regional climates were doing, even though they suffer from poorer resolution than ice cores (worms churn the sediment, obscuring records of all but the longest-lasting temperature changes). These days when one goes to hear a talk on ancient climates of North America, one is likely to learn that the speaker was forced into early retirement from the U. Geological Survey by budget cuts. It could no longer do so if it lost the extra warming from the North Atlantic.
It has been called the Nordic Seas heat pump. And it sometimes changes its route dramatically, much as a bus route can be truncated into a shorter loop. One of the most shocking scientific realizations of all time has slowly been dawning on us: the earth's climate does great flip-flops every few thousand years, and with breathtaking speed. Like bus routes or conveyor belts, ocean currents must have a return loop. If blocked by ice dams, fjords make perfect reservoirs for meltwater. The Great Salinity Anomaly, a pool of semi-salty water derived from about 500 times as much unsalted water as that released by Russell Lake, was tracked from 1968 to 1982 as it moved south from Greenland's east coast. Yet another precursor, as Henry Stommel suggested in 1961, would be the addition of fresh water to the ocean surface, diluting the salt-heavy surface waters before they became unstable enough to start sinking. This salty waterfall is more like thirty Amazon Rivers combined. Even the tropics cool down by about nine degrees during an abrupt cooling, and it is hard to imagine what in the past could have disturbed the whole earth's climate on this scale. We may not have centuries to spare, but any economy in which two percent of the population produces all the food, as is the case in the United States today, has lots of resources and many options for reordering priorities. We might, for example, anchor bargeloads of evaporation-enhancing surfactants (used in the southwest corner of the Dead Sea to speed potash production) upwind from critical downwelling sites, letting winds spread them over the ocean surface all winter, just to ensure later flushing. Ancient lakes near the Pacific coast of the United States, it turned out, show a shift to cold-weather plant species at roughly the time when the Younger Dryas was changing German pine forests into scrublands like those of modern Siberia. The sheet in 3 sheets to the wind crossword. A lake surface cooling down in the autumn will eventually sink into the less-dense-because-warmer waters below, mixing things up. There is, increasingly, international cooperation in response to catastrophe—but no country is going to be able to rely on a stored agricultural surplus for even a year, and any country will be reluctant to give away part of its surplus.
This was posited in 1797 by the Anglo-American physicist Sir Benjamin Thompson (later known, after he moved to Bavaria, as Count Rumford of the Holy Roman Empire), who also posited that, if merely to compensate, there would have to be a warmer northbound current as well. Five months after the ice dam at the Russell fjord formed, it broke, dumping a cubic mile of fresh water in only twenty-four hours. We must look at arriving sunlight and departing light and heat, not merely regional shifts on earth, to account for changes in the temperature balance. We might create a rain shadow, seeding clouds so that they dropped their unsalted water well upwind of a given year's critical flushing sites—a strategy that might be particularly important in view of the increased rainfall expected from global warming. Sudden onset, sudden recovery—this is why I use the word "flip-flop" to describe these climate changes. By 125, 000 years ago Homo sapienshad evolved from our ancestor species—so the whiplash climate changes of the last ice age affected people much like us. The expression three sheets to the wind. A muddle-through scenario assumes that we would mobilize our scientific and technological resources well in advance of any abrupt cooling problem, but that the solution wouldn't be simple. Thermostats tend to activate heating or cooling mechanisms abruptly—also an example of a system that pushes back. In almost four decades of subsequent research Henry Stommel's theory has only been enhanced, not seriously challenged. Greenland looks like that, even on a cloudless day—but the great white mass between the occasional punctuations is an ice sheet.
We need heat in the right places, such as the Greenland Sea, and not in others right next door, such as Greenland itself. Again, the difference between them amounts to nine to eighteen degrees—a range that may depend on how much ice there is to slow the responses. A remarkable amount of specious reasoning is often encountered when we contemplate reducing carbon-dioxide emissions. Now we know—and from an entirely different group of scientists exploring separate lines of reasoning and data—that the most catastrophic result of global warming could be an abrupt cooling. But our current warm-up, which started about 15, 000 years ago, began abruptly, with the temperature rising sharply while most of the ice was still present.
For Europe to be as agriculturally productive as it is (it supports more than twice the population of the United States and Canada), all those cold, dry winds that blow eastward across the North Atlantic from Canada must somehow be warmed up. Many ice sheets had already half melted, dumping a lot of fresh water into the ocean. Huge amounts of seawater sink at known downwelling sites every winter, with the water heading south when it reaches the bottom. Feedbacks are what determine thresholds, where one mode flips into another. It's also clear that sufficient global warming could trigger an abrupt cooling in at least two ways—by increasing high-latitude rainfall or by melting Greenland's ice, both of which could put enough fresh water into the ocean surface to suppress flushing. That's how our warm period might end too. A quick fix, such as bombing an ice dam, might then be possible. Increasing amounts of sea ice and clouds could reflect more sunlight back into space, but the geochemist Wallace Broecker suggests that a major greenhouse gas is disturbed by the failure of the salt conveyor, and that this affects the amount of heat retained.
These northern ice sheets were as high as Greenland's mountains, obstacles sufficient to force the jet stream to make a detour. By 1971-1972 the semi-salty blob was off Newfoundland. Greenland's east coast has a profusion of fjords between 70°N and 80°N, including one that is the world's biggest. The last time an abrupt cooling occurred was in the midst of global warming.
Unlike most ocean currents, the North Atlantic Current has a return loop that runs deep beneath the ocean surface. It's happening right now:a North Atlantic Oscillation started in 1996. Change arising from some sources, such as volcanic eruptions, can be abrupt—but the climate doesn't flip back just as quickly centuries later. We could go back to ice-age temperatures within a decade—and judging from recent discoveries, an abrupt cooling could be triggered by our current global-warming trend. Thus we might dig a wide sea-level Panama Canal in stages, carefully managing the changeover. Subarctic ocean currents were reaching the southern California coastline, and Santa Barbara must have been as cold as Juneau is now. Judging from the duration of the last warm period, we are probably near the end of the current one. It, too, has a salty waterfall, which pours the hypersaline bottom waters of the Nordic Seas (the Greenland Sea and the Norwegian Sea) south into the lower levels of the North Atlantic Ocean.
A nice little Amazon-sized waterfall flows over the ridge that connects Spain with Morocco, 800 feet below the surface of the strait. The fact that excess salt is flushed from surface waters has global implications, some of them recognized two centuries ago. Futurists have learned to bracket the future with alternative scenarios, each of which captures important features that cluster together, each of which is compact enough to be seen as a narrative on a human scale. Recovery would be very slow. Canada's agriculture supports about 28 million people. There is another part of the world with the same good soil, within the same latitudinal band, which we can use for a quick comparison. North-south ocean currents help to redistribute equatorial heat into the temperate zones, supplementing the heat transfer by winds. That might result in less evaporation, creating lower-than-normal levels of greenhouse gases and thus a global cooling. For a quarter century global-warming theorists have predicted that climate creep is going to occur and that we need to prevent greenhouse gases from warming things up, thereby raising the sea level, destroying habitats, intensifying storms, and forcing agricultural rearrangements. In the first few years the climate could cool as much as it did during the misnamed Little Ice Age (a gradual cooling that lasted from the early Renaissance until the end of the nineteenth century), with tenfold greater changes over the next decade or two. A slightly exaggerated version of our present know-something-do-nothing state of affairs is know-nothing-do-nothing: a reduction in science as usual, further limiting our chances of discovering a way out.
Now only Greenland's ice remains, but the abrupt cooling in the last warm period shows that a flip can occur in situations much like the present one. The only reason that two percent of our population can feed the other 98 percent is that we have a well-developed system of transportation and middlemen—but it is not very robust. Door latches suddenly give way. It then crossed the Atlantic and passed near the Shetland Islands around 1976. Though combating global warming is obviously on the agenda for preventing a cold flip, we could easily be blindsided by stability problems if we allow global warming per se to remain the main focus of our climate-change efforts. Obviously, local failures can occur without catastrophe—it's a question of how often and how widespread the failures are—but the present state of decline is not very reassuring. In Broecker's view, failures of salt flushing cause a worldwide rearrangement of ocean currents, resulting in—and this is the speculative part—less evaporation from the tropics. This cold period, known as the Younger Dryas, is named for the pollen of a tundra flower that turned up in a lake bed in Denmark when it shouldn't have. Thus the entire lake can empty quickly. There seems to be no way of escaping the conclusion that global climate flips occur frequently and abruptly. When that annual flushing fails for some years, the conveyor belt stops moving and so heat stops flowing so far north—and apparently we're popped back into the low state.
Seawater is more complicated, because salt content also helps to determine whether water floats or sinks. Out of the sea of undulating white clouds mountain peaks stick up like islands. History is full of withdrawals from knowledge-seeking, whether for reasons of fundamentalism, fatalism, or "government lite" economics. It was initially hoped that the abrupt warmings and coolings were just an oddity of Greenland's weather—but they have now been detected on a worldwide scale, and at about the same time.