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« on: October 07, 2005, 01:31:38 AM »

by Mike Davis
reprinted from:
     The genesis of two category-five hurricanes (Katrina and Rita) in a row over the Gulf of Mexico is an unprecedented and troubling occurrence. But for most tropical meteorologists the truly astonishing 'storm of the decade' took place in March 2004. Hurricane Catarina - so named because it made landfall in the southern Brazilian state of Santa Catarina - was the first recorded south Atlantic hurricane in history.

Textbook orthodoxy had long excluded the possibility of such an event; sea temperatures, experts claimed, are too low and wind shear too powerful to allow tropical depressions to evolve into cyclones south of the Atlantic Equator. Indeed, forecasters rubbed their eyes in disbelief as weather satellites downlinked the first images of a classical whirling disc with a well-formed eye in these forbidden latitudes.

In a series of recent meetings and publications, researchers have debated the origin and significance of Catarina. A crucial question is this: was Catarina simply a rare event at the far outlier of the normal bell curve of South Atlantic weather (in the same sense, for example, as Joe DiMaggio's incredible 56-game hitting streak in 1941 - an analogy made famous by Stephen Jay Gould), or was Catarina a 'threshold' event, signaling some fundamental and abrupt change of state in the climate system?

Scientific discussions of environmental change and global warming have long been haunted by the specter of nonlinearity. Climate models, like econometric models, are easiest to build and understand when they are simple linear extrapolations of well-quantified past behavior: when causes maintain a consistent proportionality to their effects.

But all the major components of global climate - air, water, ice and vegetation - are actually nonlinear: at certain thresholds they switch from one state of organization to another, with catastrophic consequences for species too finely-tuned to the old norms. Until the early 1990s, however, it was generally believed that these major climate transitions took centuries if not millennia to accomplish. Now, thanks to the decoding of subtle signatures in ice cores and sea-bottom sediments, we know that global temperature and ocean circulation can change abruptly - in a decade or even less.

The paradigmatic example is the so-called 'Younger Dryas' event, 12,800 years ago, when an ice dam collapsed, releasing an immense volume of meltwater from the shrinking Laurentian ice-sheet into the Atlantic Ocean via the instantly-created St. Lawrence River. The freshening of the North Atlantic suppressed the northward conveyance of warm water by the Gulf Current and plunged Europe back into a thousand-year ice age.

Abrupt switching mechanisms in the climate system, like relatively small changes in ocean salinity, are augmented by causal loops that act as amplifiers. Perhaps the most famous example is sea-ice albedo: the white, frozen Arctic Ocean reflects heat back into space, thus providing positive feedback to cooling trends; alternatively, shrinking sea-ice increases heat absorption and accelerates its own melting and planetary warming.

Thresholds, switches, amplifiers, chaos - contemporary geophysics assumes that earth history is inherently revolutionary. This is why many prominent researchers - especially those who study topics like ice sheet stability and North Atlantic circulation - have always had qualms with the consensus projections of the Intergovernmental Panel on Climate Change (IPCC), the world authority on global warming.

In contrast to Bushite flat-earthers and shills for the oil industry, their skepticism has been founded on the fear that the IPCC models fail to adequately allow for catastrophic nonlinearities like the Younger Dryas or Hurricane Catarina. Where other researchers model late 21st-century climate upon the precedents of the Altithermal (the hottest phase of the current Holocene, 8000 years ago) or the Eemian (the previous and warmer interglacial episode, 120,000 years ago); they toy with the possibilities of runaway warming returning the earth to the torrid chaos of the Paleocene-Eocene Thermal Maximum (PETM: 55 million years ago) when extreme and rapid heating of the oceans led to massive extinctions.

Dramatic new evidence has emerged recently that we may be headed, if not back to the dread and almost inconceivable PETM, then at least toward a much harder landing than envisioned by the IPCC.

As I flew toward Louisiana and the carnage of Katrina three weeks ago, I perused the 23 August issue of EOS, the newsletter of the American Geophysical Union. I was pole-axed by an article entitled "Arctic System on Trajectory to New, Seasonally Ice-Free State,' co-authored by 21 scientists from almost as many universities and research institutes. Even two days later, walking among the ruins of the Lower Ninth Ward, I found myself worrying more about the EOS article than the disaster surrounding me.

The article begins with a recounting of trends familiar to any reader of the Tuesday science section of the New York Times: for almost 30 years Arctic sea ice has been thinning and shrinking so dramatically that "a summer ice-free Arctic Ocean within a century is a real possibility." It adds, however, the new observation that this process is probably irreversible: "surprisingly, it is difficult to identify a single feedback mechanism within the Arctic that has the potency or speed to alter the system's present course."

An ice-free Arctic Ocean has not existed for at least one million years and the authors warn that the earth is inexorably headed toward a "super-interglacial" state "outside the envelope of glacial-interglacial fluctuations that prevailed during recent Earth history." They emphasize that within a century global warming will probably exceed the Eemian temperature maximum and thus obviate all the models that have used this as a likely scenario. They also suggest the total or partial collapse of the Greenland Ice Sheet is a real possibility - an event that would definitely throw a Younger Dryas wrench into the Gulf Current.

We are living, in other words, on a runaway train that is picking up speed as it passes the stations marked 'Altithermal' and 'Eemian.' 'Out of the envelope,' moreover, means that we are not only leaving behind the serendipitous climatic parameters of the Holocene - the last 10,000 years of mild, warm weather that has favored the explosive growth of agriculture and urban civilization - but also of the late Pleistocene that fostered the evolution of Homo sapiens in eastern Africa.

Other researchers undoubtedly will contest the extraordinary conclusions of the EOS article and - we must hope - suggest counterveiling forces to this scenario of an Arctic albedo catastrophe. But for the time being, at least, research on global change is pointing toward worst-case scenarios.

All of this, of course, is a perverse tribute to industrial capitalism and extractive imperialism as geological forces so formidable that they have succeeded in scarcely more than two centuries - indeed, mainly in the last fifty years - in knocking the earth off its climatic pedestal and propelling it toward the nonlinear unknown.

The demon in me wants to say: party and make merry. No need now to worry about Kyoto, recycling your aluminum cans or using too much toilet paper, when we'll soon be debating how many hunter-gathers can survive in the scorching deserts of New England or the tropical forests of the Yukon.

The good parent in me, however, screams: how is it possible that we can now contemplate with scientific seriousness whether our childrens' children will themselves have children? Let Exxon answer that in one of their sanctimonious ads.
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