You can blame El Nino for a lot of wacky weather around the world — droughts in the rain forests and floods in the deserts — but according to a new analysis by leading climate scientists, try as you might, you can’t blame this naturally recurring phenomenon for global warming.
Which is too bad, in a way. Wouldn’t it be nice to find something other than the rising concentrations of greenhouse gases that humans are pumping into the atmosphere to explain the quickening pace of climate changes around us? (This NASA image shows the places feeling rising global temperatures during the last
decade — the warmest on record.)
If you were looking for a natural explanation of rising global temperatures, the comings and goings of what scientists call the “El Nino-Southern Oscillation” — ENSO, for short — is certainly a likely suspect.
Nothing more dramatically rearranges the meteorological furniture around the planet than this large, irregularly periodic episode of unusually warm tropical Pacific Ocean surface temperatures and altered atmospheric features. Every four years or so, a big pool of especially warm tropical water that the tradewinds push up against the coast of equatorial Asia begins to spread eastward.
Months later, when this warmth reaches the shore of South America, the eastern half of the equatorial Pacific is warm rather than cool, and many things about the atmosphere are different. The rains that normally swamp southeastern Asia now fall out in the central Pacific, bringing drought to the jungles of Asia and torrential rains to Peru. In the Northern Hemisphere’s winter, the jet stream bends farther south, bringing this tropical moisture into the US Southwest and across the South. And no doubt about it, during El Nino, global temperatures are warmer than they otherwise would be.
Last year, some Australian researchers took a look at global temperature statistics in relation to the El Nino Southern Oscillation and concluded that El Nino accounts for 68 percent of global temperatures in one 50-year data set and 72 percent of a 29-year record. Their study, they said, showed “that natural climate forcing associated with ENSO is a major contributor to variability and perhaps recent trends in global temperature, a relationship that is not included in current global climate models.”
Well, an international team of climate researchers, commenting in the new issue of the Journal of Geophysical Research, clearly is not impressed with this work. For several technical reasons having to do with manipulation of different data sets, the scientists conclude that the Australians overstated El Nino’s role and understated other influences on global temperatures.
“The suggestion in their conclusions that ENSO may be a major contributor to recent trends in global temperatures is not supported by their analysis or any physical theory presented in their paper, especially as the analysis method itself eliminates the influence of trends on the purported correlations,” the new analysis concludes. Oh, and by the way, they note, the effect of ENSO on global temperatures is indeed simulated by climate models.
While it might have been convenient to pass off the current changes in climate to El Nino’s behavior, there is another way to look at this. If this big, ornery natural temperature shift were really responsible for all of the changes underway in the atmosphere and the ocean, our future would be out of our hands.
IMAGE: NASA, Robert Simmon