Today's atmospheric carbon-dioxide levels are higher than at any time in the past 800,000 years, about twice the previously confirmed time frame. Eric Wolff, of the British Antarctic Survey, led a team that drilled and analyzed the oldest--and at two miles, the longest--ice samples ever extracted. Air bubbles trapped in the ice offer scientists tiny windows on to ancient atmospheric composition. They found that changes in greenhouse-gas levels altered climate throughout this period, and that no increase matched the trend initiated by the industrial revolution 200 years ago. "We have no analogue for what will happen next," Wolff said. Wolff was referring to the climate, but he might as well have been describing human responses to it. Humans have never changed their energy regimes on purpose, under duress.

The time span under study is so long (though a blink, geologically) that we have no good way to intuit it. Here are a few benchmarks: Homo sapiens' ancestors discovered fire about 500,000 years ago. Agriculture emerged 8,000-10,000 years ago. Historically, the atmosphere can accrue a 30 parts per million increase in carbon dioxide over 1,000 years. As the study points out, the air's carbon-dioxide content has jumped 30 ppm in just 17 years. Would that finding a solution were as simple as demonstrating the problem.