By 2100, we could be recreating a 50 million-year-old climate

Enlarge / A coal mine in Australia. Burning this ancient sunlight could bring back ancient climates, too. (credit: Max Phillips (Jeremy Buckingham MLC))

From the perspective of a living organism, the history of the Earth has included an odd combination of radical change and fortunate stability. Continents have wandered from polar to equatorial homes, mountain ranges have risen and crumbled away, and entire oceans have opened and disappeared. But even through ice ages and ice-free times, conditions have stayed within a fairly narrow window that allowed the continued existence of life.

That relative stability occurred despite the fact that our Sun has not been entirely helpful. The Sun's brightness has slowly increased as it matures. While about 1,368 watts of solar radiation bathes each square meter of the Earth's surface now, it was only around 1,000 watts when the Earth was a young planet. A little over 400 million years ago, before the first fish developed legs to explore the world above sea level, sunshine was about 50 watts per square meter less than it is today. It seems that a weaker Sun was compensated by a stronger greenhouse effect (due to higher atmospheric carbon dioxide concentrations), since the most recent few million years were actually among the coolest.

But now we're heading toward a situation where the Sun is brighter and we're going to have greenhouse gas levels not seen for millions of years. What might that combination produce?

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