An Early Start for Greenhouse Warming?

摘要

Humans held sway over climate long before the belching smokestacks and spewing tailpipes of the past century or two, according to paleoclimatologist William Ruddiman. Nineteenth-century industrialization didn't kick off global warming, Ruddiman told a packed ballroom at the meeting. Instead, humans started slowly ratcheting up the thermostat as early as 8000 years ago, when they began clearing forests for agriculture, and 5000 years ago with the arrival of wet-rice cultiva- tion. The greenhouse gases carbon dioxide and methane given off by these changes in land use would have warmed the world by about 0.8℃, Ruddiman calculates.