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mit_catastrophe39 karma

The present rate of CO2 increase is much larger than in past disruption events. However, the critical rate of change seen in past events is only part of the story. First. the timescale of the current situation (about a century) is much shorter than past events. Second, natural processes in the oceans tend to damp perturbations of CO2, at a roughly 10,000 year timescale. The upshot is that the critical rate of the modern event must be rescaled by a factor of about 100/10000 = 0.01 to be compared to past catastrophes. When that rescaling is done, our modern disruption event, if it continues throughout this century, looks fairly similar to the runup to extreme warming events of the past, including those associated with mass extinction. A rough estimate is that the tipping point would occur late in this century. For more detail, see our papers here and here.

But that too is only part of the story. If the tipping point is real, our own calculations suggest a roughly 10000-yr trajectory during which things become progressively worse—but only if there were no negative feedbacks beyond those we currently understand that would act to arrest the trajectory. And we would imagine that new technologies—or simply improved scientific understanding—might contribute towards goading the Earth system in the right direction.

mit_catastrophe16 karma

Thanks for the great question! One interesting phenomenon that really matches the idea of the canary is that of “early warning signals”: basically, mathematical theory predicts that a system that’s about to cross a tipping point will start fluctuating more slowly, and this can be measured. There is a lot of work going into assessing elements of the climate system that might have tipping points, and searching for such early warning signals: one recent example is the Atlantic Meridional Overturning Circulation (AMOC; think Gulf stream). Recent work (e.g. Boers 2021) suggests that the AMOC is currently exhibiting early warning signals for collapse.

With respect to the global-scale disruption events, we could say that the canary is the historical record itself. Appropriately analyzed, the record suggests that there is a critical rate of CO2 perturbation at which mass extinction occurs, and that we are on track to cross the threshold by 2100 (see also this comment). Nevertheless, since it may take thousands of years for the ultimate consequences to play out, actions we take today to mitigate this could still have an effect.

mit_catastrophe15 karma

Thanks for the question! Unfortunately the question of how well equipped we are to survive the coming changes is pretty complex and somewhat outside of our specific expertise (we’ve been focusing more on the changes themselves). Understanding this involves not just scientific knowledge from a range of disciplines but also knowledge from social sciences about how societies will respond, what’s possible in terms of economics and policy, and so on.

We agree with you that the food question is a really important one. We’re also not experts on agriculture, but there are some other researchers and research institutes doing great work on this. Off the top of our heads, one prominent recent study is that of Gerten et al. (2020): they argue that it should in principle be possible to transform the global food system to feed 10 billion people in away that’s relatively globally sustainable. Whether this is going to be possible in practice, of course, is another matter.

mit_catastrophe12 karma

Thanks for the question! Our knowledge of Graham Hancock’s work is currently limited to a few internet searches (Dan) and a few episodes of his Netflix show (Constantin), but we wanted to make sure we got around to answering this.

A first important point is that our own work focuses on catastrophes that occurred much further back in time: many millions of years rather than tens of thousands, and way before humans even evolved as a species. So our own technical knowledge is still rather different than that needed to evaluate archaeological claims about past civilizations, and to productively wade into the debate surrounding his work.

The events themselves are also rather different in scale: any extinction that may have occurred during the Younger Dryas is still relatively minor in the grand history of life (if otherwise, this would have been observed in the fossil record), while some of the events we’ve been considering genuinely wiped out a large fraction of species present at the time.

On the whole (and speaking now more generally), we do think that questions of past climate changes and societal collapse are interesting ones that deserve to be looked at. Beyond pure intellectual interest, better understanding whether/how climate changes caused collapse in the past seems quite important for humanity’s future.

mit_catastrophe11 karma

Thanks for your question! Whatever we do, over hundreds of millions of years there will probably be a mass extinction at some point, most simply because there have been 5 mass extinctions in the last 500 million years. That said, there appears to be an unprecedented rate of species loss today, and many would argue that we are already in the sixth mass extinction (see for example Elizabeth Kolbert’s book, or this paper).

Changes in land use probably account for much modern species loss. Climate change and ocean acidification (which we’ve focused on in our work) may eventually contribute to much more. The best way to prepare for this as a society is clearly to act in ways that limit disruptions to the global environment. At the individual level, the question becomes about how to best influence the actions of societies, which is unfortunately outside of our domain of expertise.