[BEIJING] Chinese scientists have gained insight into the factors affecting the strength of the Asian monsoon in the last 200,000 years.
Wang Yongjin from Nanjing Normal University and colleagues published their study in Nature last week (28 February).
They took samples of stalagmites — known as speleothems — from the Sanbao Cave in eastern central China and analysed their oxygen isotope ratios, which are linked to rainfall and provide a record of the climate at the time.
Adding these data to their previous work has enabled the research team to compile a 224,000-year record of the Asian monsoon's variability.
According to the study, the monsoon responds primarily to changes in summer solar radiation in the Northern Hemisphere. "The synchronous relation between monsoon and the summer solar radiation means that we can predict weather through astronomical orbits in the future," says Wang.
Until now, the best high-resolution records of climate variability from the Northern Hemisphere go back only to the last interglacial period, less than 125,000 years ago.
"We are able to date [the samples] precisely and work on samples hundreds of thousands of years old, far beyond the limit of about 50,000 years that radiocarbon dating allows," Wang told SciDev.Net.
The new study also provides a complete record of 'Chinese interstadials' — strong summer monsoon events that occur every 1,000 years — and shows that these events are affected by the volume of ice in the area at the time.
But Wang points out that this rule may not be suitable for inferring climate change since the eighteenth century, as human impacts on climate change have been greatly enhanced since the Industrial Revolution.
Despite the new findings, research in the palaeoclimatic sector remains a challenge.
"The foremost goal is, of course, is to anticipate how the Asian monsoon might change in the future," write Jonathan Overpeck and Julia Cole of the US-based University of Arizona in an accompanying News and Views article.
They write that, while climate change could cause the Asian monsoon to provide more rain to those who need it, a stronger monsoon would be hard on parts of south and east Asia that are already plagued by summer flooding.
Reference: Nature 451, 1090 (2008)