Tree rings reveal secrets of global weather patterns
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E-mail Xinhua, February 7, 2012
An iconic New Zealand tree, once logged extensively for its famous hard wood, is helping New Zealand scientists understand two major weather patterns that have had a deadly influence across the Asia-Pacific region.
Researchers at the University of Auckland have been studying the rings of the native New Zealand kauri tree to gain an insight into how the periodical El Nino and La Nina weather patterns had affected the country over the last seven centuries.
The two patterns, which fluctuate over the Pacific Ocean, would become even more dominant in New Zealand with climate change, they forecast.
"As the world continues to warm, New Zealand is likely to experience the impacts of El Nino and La Nina events with comparable intensity and frequency to what we have seen over the last three decades, and possibly more so," said lead researcher Dr Anthony Fowler, of the School of Environmental Science.
"This means that we should anticipate more extreme events, such as flooding and droughts, in the regions affected by these weather patterns," he said in a statement.
In New Zealand, El Nino events usually brought more cool southwesterly winds, making the whole country relatively cool with associated droughts in sheltered eastern areas of both islands.
The winds reversed with La Ninas, when moisture laden air from the sub tropics elevated temperatures, especially in the North Island, and brought higher rainfall to much of the country, sometimes with floods.
"The El Nino-La Nina phenomenon has been referred to as the heartbeat of the world," said Fowler.
"After the seasonal cycle and monsoons, it's the most important source of year-on-year climate variation. Strong events often cause incredible damage and affect hundreds of millions of people around the world. El Ninos, in particular, have been responsible for some of the devastating 20th century droughts in Australia, floods in South America, and failure of the monsoons in India," he said.
Last year, the La Nina pattern caused severe drought in New Zealand's Pacific island neighbors of Tokelau and Tuvalu.
"To date the global climate models used to 'predict' the future have been unable to give us a clear picture of what will happen with El Nino and La Nina as the world warms.
"But understanding the phenomenon is critical to learning what climate change will mean for the world's population.
"The premise of our work is that we know that the world has warmed over the last few centuries and we can look back to see what has happened with El Nino-La Nina over that time. By studying how the phenomenon has behaved in the past we can anticipate what might plausibly happen in the future. This should result in more informed scenarios of future regional climate change."
The scientists studied the climate record in the rings of kauri trees dating back to 1300, which provided a detailed record of El Nino and La Nina events.
"Kauri trees are quite sensitive to these weather patterns," said Fowler.
"During El Nino events they grow rapidly and have wide tree rings whereas during La Nina events they grow more slowly and have narrow rings."
Notably wide and narrow kauri tree rings had become more frequent as the world warmed over the last few centuries, indicating that El Nino and La Nina events had become more frequent or intense as the world warmed, or that New Zealand's climate was more strongly influenced by such events.
"Either possibility suggests that droughts and floods related to El Ninos and La Ninas will continue to significantly affect New Zealand, and may well become more intense."
The team managed to piece together the data from living trees and the timbers of old homes, he said.
"Kauri logging in the 19th and early 20th Century devastated the landscape," he said.
"But a lot of the wood that was cut down can still be found in the weatherboards of our houses and provided important data for our research."
The next phase of the research, which was almost complete, involved adding data from kauri trees preserved in swamps to extend the record back almost 4,000 years, which could help show whether the El Nino-La Nina activity in the 20th Century was the most intense ever, as suggested by available records, or a return to conditions that had occurred in the past.
The research, funded by the New Zealand Foundation for Research Science and Technology and a grant from the Royal Society of New Zealand, was published in the journal Nature Climate Change.
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