Luboš Motl: CO2 may lag temperature just by 400 years or so

Phys.ORG is among the most science-oriented outlets that inform about the new paper

Tightened constraints on the time-lag between Antarctic temperature and CO2 during the last deglaciation (full text PDF)

by Pedro, Rasmussen, and Ommen published in Climate of the Past. The content of the paper is simple.

They looked at the Antarctic data between 17,000 BC and 9,000 BC (to help delayed readers of this blog in the year 3000 AD, I express the timing relatively to Jesus Christ instead of our humble present). The CO2concentration increases or decreases after the temperature does the same thing but the newly determined lag is just about 400 years instead of the figure 800 years we loved to repeat.

It’s still safely positive so that we know which change is the cause (temperature change, caused mostly by the Milankovitch cycles) and which change is the consequence (changes of CO2 due to the temperature-dependent ability of ocean water to store trace gases).

However, it’s also much shorter than we used to say. It means that the excess CO2 we are adding into the atmosphere disappears much earlier than those 800 years we used to promote. Based on the currently observed CO2 budget, it seems obvious to me that the excess CO2 in the atmosphere would be reduced e-times within 50 years or so, much shorter even than their estimate of 400 years. But the motion of CO2could have been slower when (and where) the Earth was cooler and less hospitable for life.

(Again, it’s easy to calculate the 50-year figure. The amount of CO2 we are emitting would increase the CO2 concentration by 4 ppm a year. The actual observed increase is about 1.9 ppm in average. So it’s clear that Nature – oceans and the biosphere – are absorbing 2.1 ppm out of the excess CO2 every year. This absorption only depends on the elevated concentration because that’s the only thing that the oceans and plants “feel”. So it would continue even if we stopped all CO2 emissions. Consequently, CO2 would start to drop by 2.1 ppm a year although the decrease would be gradually slowing down. The current excess CO2, 393-280 ppm = 113 ppm or so, would be largely undone in 50 years or so. The CO2 concentration would quickly return to the level compatible with the equilibrium given the current interglacial temperatures – and it makes no difference whether you add the tiny man-made contribution to the interglacial temperatures or not. The modest warming arguably caused by CO2 would be undone in those 50 years, too.)

The Reference Frame

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