Did Chinese rice farmers kick off global warming 5000 years ago?

That's the question raised by a new study I report on in a brief news item in today's issue of Science. Rice farming takes place in a wetlands environment and produces a lot of methane, an important greenhouse gas. The link requires online access to the journal (a very good investment for anyone interested in science), but I am providing the text of it below.

Actually, as I quote University College London archaeologist Dorian Fuller, we should also be looking at the possible role of early cattle farming, which began nearly 10,000 years ago in the Near East. It looks as though the human carbon footprint may date from way back in prehistory, although I should stress that Ruddiman's hypothesis remains controversial. If you want to read more, check out his book on the subject, "Plows, Plagues, and Petroleum: How Humans Took Control of Climate."

Here's my story:

WAS CHINA AN EARLY EMITTER?

Last year, China overtook the United States as the world's leading emitter of greenhouse gases. But archaeological evidence suggests that the Chinese are old hands at global warming: Rice farmers may have begun making significant contributions thousands of years ago.

A Chinese-U.S. team led by William Ruddiman, a paleoclimatologist emeritus at the University of Virginia, Charlottesville, surveyed 311 archaeological sites in rice-growing regions of China. It found that between 6000 and 4000 years ago, the number of sites increased almost 10-fold. The timing coincides with evidence from other studies that atmospheric levels of methane, a byproduct of many farming activities, including wetland rice cultivation, began to increase about 5000 years ago. These findings, published in the July issue of Quaternary Science Reviews, are in line with Ruddiman's controversial earlier claims that human contributions to global warming began long before the industrialization of the 19th century (Science, 16 January 2004, p. 306).

Dorian Fuller of University College London, an expert in prehistoric Chinese agriculture, says the study adds "important and compelling" information in support of Ruddiman's hypothesis. He says climate modelers should also start looking at other early sources of atmospheric methane, such as cattle herding, which likewise increased dramatically about 5000 years ago.

Other climate warnings: Science's online news service, ScienceNOW, has two news items today about the effects of global warming on animal life--one about fish, and the other corals. The links are free for four weeks beginning today.

Obama Update: Slate writers Doug Kendall and Dahlia Lithwick pen a very intelligent analysis of Obama's rightward shift in a piece called "Constitutional Drift: Obama veers to the right, but does he need to take the Constitution with him?"