The weakest El Niño activity happened during the Medieval Climate Anomaly in the 11th century, whereas the strongest activity has been since the 18th century. The tree rings reveal that the intensity of El Niño has been highly variable, with decades of strong El Niño events and decades of little activity. “The coral records, however, are brief, whereas the tree-ring records from North America supply us with a continuous El Niño record reaching back 1100 years.” “Our work revealed that the towering trees on the mountain slopes of the US Southwest and the colorful corals in the tropical Pacific both listen to the music of El Niño, which shows its signature in their yearly growth rings,” explains Li. Credit: Image courtesy International Pacific Research Center
Bristlecone trees, such as this over a thousand-year-old tree in the Great Basin National Park, contributed to the tree-ring record on El Niño. The tree-ring records, furthermore, match well existing reconstructions of the El Niño-Southern Oscillation and correlate highly, for instance, with δ 18O isotope concentrations of both living corals and corals that lived hundreds of years ago around Palmyra in the central Pacific. During El Niño, the unusually warm surface temperatures in the eastern Pacific lead to changes in the atmospheric circulation, causing unusually wetter winters in the US Southwest, and thus wider tree rings unusually cold eastern Pacific temperatures during La Niña lead to drought and narrower rings. Tree rings in the US Southwest, the team found, agree well with the 150-year instrumental sea surface temperature records in the tropical Pacific. The study, spearheaded by Jinbao Li, International Pacific Research Center, University of Hawai’i at Manoa, is published in the May 6 issue of Nature Climate Change. An international team of climate scientists has now shown that annually resolved tree-ring records from North America, particularly from the US Southwest, give a continuous representation of the intensity of El Niño events over the past 1100 years and can be used to improve El Niño prediction in climate models. Predicting El Niño events more than several months ahead is now routine, but predicting how it will change in a warming world has been hampered by the short instrumental record. Tree Rings Tell a 1100-Year History of El NiñoĮl Niño and its partner La Niña, the warm and cold phases in the eastern half of the tropical Pacific, play havoc with climate worldwide. Superimposed on a general rising trend, cycles of strong activity occurred about every 50–90 years. (Individual El Niño events occur typically at intervals of 2-‐7 years.) Periods of strong El Niño activity are indicated by amplitudes above 1.0.
The green curve represents the long-‐term trend in El Niño strength. El Niño amplitude derived from North American tree rings (blue) and instrumental measurements (red). The test will be when somebody asks for the data for replication purposes. So I’m inclined to trust this reconstruction a bit more than I’d trust Mann’s. In a desert, water is the limiting factor for growth, temperature, not so much. I’ve covered the issue of “treemometers” here and here previously, and they are worth a read as a refresher for this new paper.ĭuring El Niño, the unusually warm surface temperatures in the eastern Pacific lead to changes in the atmospheric circulation, causing unusually wetter winters in the US Southwest, and thus wider tree rings unusually cold eastern Pacific temperatures during La Niña lead to drought and narrower rings. Why? Well it has to do with the Bristlecone pine being a better proxy for precipitation than temperature, and as we know, El Niño gives some significant precipitation impacts to the desert southwest. Like Mann et al, they combined the recent instrumental record of ENSO variation with the proxy reconstruction record, except they didn’t need to delete any data, nor cover up any curves that didn’t behave as they wished. Our old friend the Bristlecone pine in the southwest USA is the test subject again. From the University of Hawai’i’s International Pacific Research Center at Mānoa, comes this proxy reconstruction that does some similar things the infamous hockey stick reconstruction, but doesn’t need to pull any statistical “tricks” to make the case.
0 kommentar(er)
