Earth ‘Entering New Extinction Phase’

20 06 2015
Mark Cochrane

Mark Cochrane

More from Mark Cochrane this time on the current media doing the rounds regarding the sixth great extinction event underway.

I haven’t read the paper yet but it is another along the lines of others already out showing that we are, in fact, causing the sixth mass extinction right now. The last mass extinction killed off the dinosaurs, so we should feel privileged to be living in such momentous times and appalled at our culpability. The ‘good’ news of this study is that we may only be causing extinctions of vertebrate species at 114 times of levels that would be occurring without our help ( though climate change, pollution, habitat destruction) instead of the previous estimates of 1,000 times higher. On the other hand, pollination by bees may be gone within three generations, potentially taking us with it…

BBC story link

The scientists looked at historic rates of extinction for vertebrates – animals with backbones – by assessing fossil records.

They found that the current extinction rate was more than 100 times higher than in periods when Earth was not going through a mass extinction event.

Since 1900, the report says, more than 400 more vertebrates had disappeared.

Such a loss would normally be seen over a period of up to 10,000 years, the scientists say.

And the actual paper, which can be found here.

Accelerated modern human–induced species losses: Entering the sixth mass extinction

These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing.

ALSO……  a discussion on theories by a chap called Ruddiman

1) The early AGW hypothesis of Ruddiman – AGW starting around 6000BC, rice cultivation

2) The idea that glaciation would have started in Canada already if not for that early AGW (Ruddiman again)

3) How long current and projected GHG emissions will hold off a return of glaciation ?

Been reading about it here

Mark Cochrane’s response:

1) Ruddiman basically posits that through early deforestation and agriculture human beings started the current global climate change ball rolling much earlier than the industrial revolution. Deforestation and tilling up the soil started releasing substantial amounts of carbon dioxide. A bit later, domestication of animals and rice cultivation also added significant emissions of methane to the mix.

I actually like his hypothesis and think that he does a fairly good job supporting it, especially as he ties some clear wiggles in the global levels of these gases to the advent of our activities and reversals to known periods of widespread plague and land abandonment.

I’ve talked with global modelers who vehemently hate Ruddiman’s ideas. Scientists can be emotional too. The crux of the issue being that you do not necessarily need Ruddiman’s contention that we were helping to force things to explain the climate that we have inferred through climate proxies for the period in question. The argument boils down to whether there is a statistically significant signal that could ‘prove’ what he is positing. Their argument has some merit for CO2 but the methane story seems much clearer and in line with Ruddiman’s ideas. When I raised that point it shut down the dispute rather quickly. Take that for what it is worth.

The bottom line is that it is quite possible that we did start mucking up the climate somewhat even before we started using fossil fuels. However, you have to keep in mind the degree to which this was and is occurring over time. Even now, about 10% of global emissions can be tied to deforestation so it isn’t a stretch to think that those activities had the same effects in the past. Human populations were much lower and we didn’t have power tools though so the process was much slower. People tend to forget about time and logic when considering these things.

2) Glaciation in Canada – The idea is that in the little ice age, and perhaps before, we might have tipped into glacier formation/growth if it weren’t for early man’s carbon releasing activities. This one is a bit less certain but it is conceivable that this process might have kicked in during the depths of the Little Ice Age. This would yield expansion of glaciers and ice caps up in Canada and could eventually have resulted in significant albedo changes. Note though, Ruddiman’s ideas were based on earlier calculations of the Milankovitch cycles (to the best of my memory at the moment) when it was thought that we were getting close to the next ice age period. Updated calculations though show us staying in this interglacial period for several thousand years more though. So, yes we might have had some more ice formation but it is somewhat dubious if early man’s land use activities saved us from slipping into an ice age by now.

3) How long have we staved off the return of glaciation? This is a very speculative matter. If we raise the levels much higher and keep them there, we may have put an end to millions of years of ice ages altogether. The concerning matter being that there were no stable temperatures just above the cool, frequent ice age world we are used to. If we melt off the ice sheets of Antarctica and Greenland we could conceivably send the world back into a warm state when palm trees grew in the Arctic (e.g. +10-12 C). It would take thousands of years but be irreversible. However, if we don’t keep pumping the carbon levels higher and higher, then we could either stabilize levels or have them start dropping eventually. If we stop completely then we would work our way back to more reasonable levels within several thousand years. So, ultimately, it depends on what we do.

Figure 4. Effect of fossil fuel CO2 on the future evolution of global mean temperature. Green represents natural evolution, blue represents the results of anthropogenic release of 300 Gton C, orange is 1000 Gton C, and red is 5000 Gton C (Archer 2005).




One response

22 06 2015
Anthony William O'brien

The return to the non human intervention glaciation rate assumes the biosphere will continue to absorb a significant proportion of human created greenhouse gases. However, greenhouse gases will remain above natural levels pretty much permanently.

We will not return to the natural line, we will not even return to the gradient of the natural line. We have broken the clockwork of glaciation of the last million years or so.

If civilization collapses soonish, then at a bare minimum we are looking at 200,000 years for the system to re establish natural cycles. But even this wild guess is likely hopelessly optimistic. If BAU carries on for more than a decade or so, then we could be looking at tens of millions of years (and maybe already)

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