Windswept_ The Story of Wind and Weather - Marq de Villiers [42]
Take climate cycles. Perhaps the best known of these is El Nino, referred to by scientists as ENSO (for El Nino Southern Oscillation). Typical El Nino events, as they are called, last somewhere between six to eighteen months; their most obvious feature is a massive upwelling of warmer water in the eastern tropical Pacific, whose main consequences lie in the tropics but whose climatic fingerprints cause widespread droughts as far away as southern Africa and generally warmer winters in places like northeastern America. Its companion phenomenon is La Nina, which is its opposite: unusually cold Pacific temperatures. La Ninas occur after many, but not all, El Ninos; their net effect is colder-than-usual northeastern American winters and warmer southwestern temperatures. As with dry years in the Sahel, there tend to be fewer hurricanes in El Nino years; the best guess is that one doesn't cause the other, but that some still-unknown factor causes both phenomena.
It's known that in the current global climate, El Nino years are warmer and La Nina years are cooler. It's also known that in 1976 the equatorial Pacific, potentially driven by anthropogenic warming, switched from a weak La Nina state to one in which El Nino occurs with greater frequency and intensity.
Does it therefore follow that more persistent El Ninos would amplify global warming? Or that more global warming would result in more El Ninos?
Perhaps, but not necessarily. A new study has found that in the early- to mid-Pliocene (5 to 2.7 million years ago), a steamy era that was the last time that global temperatures were warmer than they are today (atmospheric temperatures probably 10 degrees higher), the Pacific system was under an extended La Nina—like state, rather than the predicted El Niiio one. These results were unexpected, and remain to be explained.20
El Ninos were first acknowledged by fishermen from Chile, and because the phenomenon generally occurred around Christmas and brought them mostly beneficial results (more fish in the up welling water), they gave it the name El Nino, which means Christ child in Spanish. La Nina, for her part, was originally referred to as el Viejo ("the old guy"), but was given its present name by the American media.
El Ninos were first plotted by a British meteorologist, Gilbert Walker, in the 1920s, from as far away as India. Walker was trying to get a grip on what caused the often sizeable fluctuations in the strength of the Indian monsoons, and discovered that strong monsoons often correlated with severe droughts in Australia, Indonesia, and southern Africa. He also noted, without interpreting them, correlations between stable periods of high pressure in the eastern Pacific and periods of low pressure in the Asian Pacific. In his journals he called this "the southern oscillation." And there it rested, until the 1950s, when climatologists finally connected his hypothesis with what the Chilean fishermen had already observed. El Nino affects everything from large-scale climatic trends to microscale events, like wildflower blooms in the southern California deserts.
It is still impossible to predict when an El Nino will happen, a simple fact that makes climate-change skeptics raise their eyebrows— if you can't predict a simple recurring cycle a year or two in the future, how can you possibly predict climate change over hundreds and even thousands of years?
El Nino is not the only "oscillation" to affect winds and weather. There are at least a dozen others, and researchers seem to be discovering more every year. I spent a few months talking to atmospheric scientists and plowing through research papers in an attempt to understand their somewhat dizzying interconnections; at one point the wall in my office was slathered with charts labeled with impenetrable acronyms (AO, NAO, PDO, MJO, QBO, and others) of dubious utility, and eventually I tore them all down. Even to scientists, the impact of most of these cycles is only hazily understood.
Still, some things