Did dinosaurs warm the world?

A sauropod
A sauropod

Possibly, by up to one and a half degrees.

This recent paper in the journal Current Biology claims that the digestive tracts of dinosaurs emitted 520 Mtonnes of methane a year, comparable to the total modern-day methane emissions. The authors suggested that this could have been an important factor in warm Mesozoic climates.

Unfortunately, they did not do any calculations of how much warmer these emissions would have made the planet. Fortunately, the PAGE09 integrated assessment model allows a rough estimate of the warming to be made.

Assuming that the climate at the time would have reacted to additional methane in the same way as the climate today does, and using the full range of climate sensitivity estimates from the IPCC, 520 Mtonnes of methane per year would have warmed the world by between 0.4 and 0.9 degC (90% confidence interval). This warming would have happened within a few decades of the emissions starting.

The authors of the Current Biology paper think that their estimate of emissions may be understated by a factor of two. If so, the warming rises to between 0.6 and 1.6 degC (90% confidence interval). The rise in temperature is not proportional to the rise in emissions because of the radiative forcing properties of methane in the atmosphere.

If the Current Biology authors are right, homo sapiens might not be the first species to alter the global climate.

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