Mass extinctions past and future

[jim mcnamara]

http://advances.sciencemag.org/content/3/9/e1700906

Abstract:

The history of the Earth system is a story of change. Some changes are gradual and benign, but others, especially those associated with catastrophic mass extinction, are relatively abrupt and destructive. What sets one group apart from the other? Here, I hypothesize that perturbations of Earth’s carbon cycle lead to mass extinction if they exceed either a critical rate at long time scales or a critical size at short time scales. By analyzing 31 carbon isotopic events during the past 542 million years, I identify the critical rate with a limit imposed by mass conservation. Identification of the crossover time scale separating fast from slow events then yields the critical size. The modern critical size for the marine carbon cycle is roughly similar to the mass of carbon that human activities will likely have added to the oceans by the year 2100.

Discussion article from phys.org:

https://phys.org/news/2017-09-mathematics-sixth-mass-extinction.html

An irreversible change in the carbon cycle will start to occur sometime at or after the year 2100. The changes will not play out instantly but over periods of thousands of years. The point in time is an estimate of the amount of additional carbon - ~216 gigatons - and an approximate time it will have been added in sufficient quantityto the oceans in order to destabilize the carbon cycle.

 

[BillTre]

Wow!

This is going to get heavily checked out because it has huge and obvious political implications.
I am no expert on this material and don't feel all that competent on deciding if this research is good or not, so I'll have to see what more knowledgeable people think.
On the other hand, he's an MIT Prof.

It will be interesting to see what happens.

 

[jim mcnamara]

It is really a gross estimate, not exact. And I do not see when the reversal of ocean carbon buildup times out - meaning if we stop adding carbon, how long will it take to get back to say, pre-1750 ocean carbon levels? Assume a long time. The year 1750 is the the approximate start of the "Industrial Age".

It is interesting.

 

[jim mcnamara]

Edit: the estimate for the amount of carbon required was reported incorrectly: it should be 310 gigatons of carbon, per the new update.

 

[BillTre]

What I find interesting is that this paper provides an easily understandable and (to me) rational cause of extinctions (exceeding the capacity of an ecosystem to deal with an excess chemical). This seems to provide a united explanation of several of the big extinctions.

It also makes the point that there are thresholds which should not be passed without possibly incurring great risk.
And whether the number is 300 or 310 Giga-tons isn't so important as that it looks like we won't have much trouble reaching either of them.

These are things that more people can understand and may base their vote on. This, seems to me, is the most likely path to a less disastrous future.