My Bookmarks on Science & Technology, Climate Change, Astrobiology, Genetics, Evolution

April 28, 2008 – Original Source: Climate Progress, by Dr. Joseph Romm

The good news: The earth’s carbon cycle has natural negative feedbacks that reverse natural surges in carbon dioxide.

The bad news: We are spewing CO2 into the atmosphere 14,000 times faster than nature has over the past 600,000 years, far too quickly for those feedbacks to respond.

This comes from “Close mass balance of long-term carbon fluxes from ice-core CO2 and ocean chemistry records,” in Nature Geosciences (subs. reqd, news article here) by Zeebe and Caldeira. Put another way:

“These feedbacks operate so slowly that they will not help us in terms of climate change … that we’re going to see in the next several hundred years,” Zeebe said by telephone from the University of Hawaii. “Right now we have put the system entirely out of equilibrium.

Zeebe notes that, “the average change in the amount of atmospheric carbon dioxide over the last 600,000 years has been just 22 parts per million by volume.” Humans have run up CO2 levels 100 ppm over the last two centuries!

In the ancient past, excess carbon dioxide came mostly from volcanoes, which spewed very little of the chemical compared to what humans activities do now, but it still had to be addressed.

This antique excess carbon dioxide — a powerful greenhouse gas — was removed from the atmosphere through the weathering of mountains, which take in the chemical….

The natural mechanism will eventually absorb the excess carbon dioxide, Zeebe said, but not for hundreds of thousands of years.

See, the skeptics were right: The planet is self-healing. You go, deniers [no, seriously, please, just go]! So my great-great-great-great — [insert 10,000 "greats" here] — great-great-great grand-kid will be doing just fine, thank you very much!

In the meantime, the rest of us will have to deal with the consequences of humanity’s self-destructive inaction and the positive or amplifying feedbacks.

The article’s full abstract is here:

Feedbacks controlling long-term fluxes in the carbon cycle and in particular atmospheric carbon dioxide are critical in stabilizing the Earth’s long-term climate. It has been hypothesized that atmospheric CO2 concentrations over millions of years are controlled by a CO2-driven weathering feedback that maintains a mass balance between the CO2 input to the atmosphere from volcanism, metamorphism and net organic matter oxidation, and its removal by silicate rock weathering and subsequent carbonate mineral burial. However, this hypothesis is frequently challenged by alternative suggestions, many involving continental uplift and either avoiding the need for a mass balance or invoking fortuitously balanced fluxes in the organic carbon cycle.

Here, we present observational evidence for a close mass balance of carbon cycle fluxes during the late Pleistocene epoch. Using atmospheric CO2 concentrations from ice cores, we show that the mean long-term trend of atmospheric CO2 levels is no more than 22 p.p.m.v. over the past 610,000 years. When these data are used in combination with indicators of ocean carbonate mineral saturation to force carbon cycle models, the maximum imbalance between the supply and uptake of CO2 is 1–2% during the late Pleistocene. This long-term balance holds despite glacial–interglacial variations on shorter timescales. Our results provide support for a weathering feedback driven by atmospheric CO2 concentrations that maintains the observed fine mass balance.


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