Well for one thing there are Dansgaard-Oeschger events, or D-O for short. Although oh-oh might be more appropriate. Those skeptical of man-made global warming orthodoxy are often smeared as “deniers” as though we denied that climate change was happening or could or that it might matter. Not a bit of it. What we deny is that there is any clear link between human behaviour and often-alarming climate swings including those “D-O events” that, long before internal combustion engines and with atmospheric CO2 at half the present level, produced sudden temperature swings beyond models’ nightmares, of over 7˚C in four decades.
Writing in Pacifica Tribune, and reprinted in Watts Up With That, Jim Steele explains that these sudden drastic changes in temperature cannot be the result of “changes in greenhouse gases or solar insolation” because they’re too sudden. So the most probable explanation is the Arctic Ocean suddenly venting heat.
As Steele admits, that explanation doesn’t sound probable at all given that the Arctic Ocean is famous above all else for being really cold. But in fact, climate being complicated, it turns out that the Gulf Stream transports warm, dense salty water north and it sinks as it approaches the Arctic, creating a rather surprising “layer of warm Atlantic water stored at depths between 300 and 2,700 feet below the Arctic Ocean’s surface”.
Surprising? Alarming would be a better word because Steele quotes researchers claiming “the total quantity of heat is substantial, enough to melt the Arctic sea ice cover several times over”. Now as has been observed, melting ice that’s already floating in the ocean is far less ominous for sea levels than ice that is currently sitting on land, in Greenland or the Antarctic. And it’s highly improbable that all this heat would get released at once. But periodically changing conditions including winds blowing the covering layer of ice out into the Atlantic (as in the 1990s, apparently) lets the warmer water get through the cold layer above it. Steele then cites anthropologists who believe the “pre-Dorsett culture” would move inland when sea ice lasted 2 months longer than it now does and temperatures were 2-4˚ colder, then came back when open water lasting 4 months longer than it currently does was accompanied by temperatures 5˚ higher.
What’s interesting about this argument is that, as Steele says, we will soon have a good empirical test of how important man-made GHGs are at least in the Arctic. “If the loss of Arctic sea ice and warmer temperatures are due to rising CO2 concentrations, we should soon see a total loss of Arctic sea ice as predicted by some climate scientists. In contrast, if natural oscillations are controlling intrusions of warm Atlantic waters, Arctic sea ice will soon rebound.” Mind you, climate is complex and so is evidence. He adds that “warmer temperatures did last for 300 years during cycles a few thousand years ago.” But in any case, if it’s predominantly natural cycles “Arctic temperatures will not experience further accelerated warming. We will soon see which theory is most accurate within the coming decade.”
What’s scary is that climate has a habit of changing suddenly. At least these D-O events seem limited to the Arctic. But temperatures have swung suddenly on a larger scale a number of times, from the “Younger Dryas” sudden cooling while the last glaciation was ending to the Paleocene-Eocene Thermal Maximum, and indeed the beginning and ending of various Pleistocene glaciations. And when temperature changes suddenly, up or down, it’s very hard to adjust to. And since it has happened over and over again without any human intervention to cause it, there is no real prospect that human intervention could stop it even if we wanted to, say, halt a sudden cooling because some dang dormant volcano suddenly wakes up and blasts cooling ash and sulphur sky-high.