Is another mass extinction looming?

No, this has nothing to do with Donald Trump. My topic is the bigger picture. Over the millennia the Earth’s biosphere has endured repeated mass extinctions. Somehow life has survived and recovered, but these events can be catastrophic. It is generally accepted that there have been five major extinctions, each of which became an evolutionary turning point, causing virtual elimination of at least 70% of all living species. Of course, life always finds a way, as the fictional mathematician in the movie Jurassic Park wryly noted. Usually different life forms assumed dominance after each catastrophe, and while evolution stuttered it nevertheless continued.

None of these events has happened since our species evolved, but that may be about to change. In fact, on a geophysical time scale, this threat may be imminent. And don’t be so sure that we will be among the survivors. This ominous prediction arises from an analysis of concentrations of oceanic carbon over time. The ocean, in case you didn’t know, typically retains fifty times as much carbon as the atmosphere, and variations in its concentration have correspondingly larger impacts on climate. Results of this study are summarized in the figure below.

The use of logarithmic scales in this diagram highlights a key point. The crucial discriminator is not the amount of carbon. Rather it is the rate of change. When carbon concentrations rise or fall very quickly, then this seems to be correlated with the occurrence of mass extinctions. This isn’t a perfect correlation and it certainly doesn’t prove causation. Rather it is a statistically meaningful indicator. Over the time frame covered by this study, there have been 31 oceanic carbon variations that exceed the margin of error, shown by the yellow band. Of these, only 10 were extreme, and the worst 5 of these closely match the major extinction events. In particular, all of the 4 excursions showing sudden increases match such events. Keep that fact in mind.

Of course, you might scoff at this correlation as a chance relationship deriving from how the data were analyzed, but there is a plausible scientific explanation for why it could be valid. Describing this requires more time and expertise than be profitably expended in this blog, and only those of you with deep scientific training would understand it anyway. So, let’s just stipulate that the threat may be real.

Now comes the good part, using that adjective very loosely. An analysis by geophysics professor Daniel H. Rothman of MIT shows that since 1850 there has been a very significant acceleration in oceanic carbon content. Recent measurements are quite precise and the data can be confidently extrapolated for coming decades. At the predicted rate of change, the world will enter the mass extinction zone in about the year 2100, give or take a decade or so. If you remain skeptical, have a look at this article.

Now remember the fact that I highlighted above. Looking again at the diagram, note that there have been no circumstances going back hundreds of millions of years when a sudden rise in carbon concentration didn’t coincide with biological disaster. None! If another such event is happening now, this will be the first for our species, and thus the first time when an extinction subject might conceivably alter or prevent it. Personally, I suspect we would survive, but the post-extinction world would be very different from what we now know.

In case you wondered, the MIT scientists ran out a number of scenarios to see if it is possible to change the threat vector sufficiently to avoid the extinction zone. Only one showed any promise at all. It requires a dramatic change in human activity starting no later than 2020. And even this only barely avoids catastrophe. Want to bet on how likely that is?

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