Mass Extinctions and CO2 levels

The chart below is adapted from a similar graph in Dr. Peter Ward's book, "Under a Green Sky." It plots all the mass extinction events of the last 500 million years against the best estimate of carbon dioxide levels (CO2) at the time. According to his analysis, all major extinctions occured when CO2 levels exceeded a thousand parts per million (ppm). 

This is a fascinating and ominous correlation, which I will explain in a moment. First, a word about Peter and the book cited above. He is well - qualified, beyond being an emminent professor at the University of Washington in Seattle. He has received many honors; was featured on some television shows; gave a talk at the highly reputed TED conferences; and has written 17 books. (Although we have recently become friends, I was a reader and fan for several years prior.)

In "Under a Green Sky" he describes the fascinating detective work, in which he participated, to understand some of the previous mass extinctions. The tedious work to decipher the geologic record in diverse places around the world, becomes an adventure.

The picture that emerges, is that over tens of millions of years, Earth's climate and life forms have changed dramatically, at times, with different causes or 'trigger events.'

He proposes that there are two different biologic modes of the planet, over the last few hundred million years. The big distinguishing factor is the state of the ocean, and its bio-chemistry. At a certain level of temperature and carbon dioxide (CO2) the sea turns purple, with a hydrogen sulfide base. When that happens, a mass extinction occurs.  A mass extinction is defined as when more than half the species disappear.

As you will see on that graph, each known mass extinction during the last 550 million years occurred when CO2 levels were over 1,000 ppm.  If you want to get an understanding of the connection, and a fascinating understanding of how leading paleontologists decipher the past, I encourage you to get this book.

The cause for concern is that the current CO2 level -- more than 390 ppm (parts per million) -- is projected to reach a thousand ppm in approximately one hundred years at the current rate of increase. The measurement of CO2 levels has been done with great precision for more than fifty years going back to the legendary work of Dr. Charles David Keeling, on a remote Hawaiian mountain top, to avoid the influence of civilization on the atmosphere. Now those measurements are also done by labs around the world. (I will cover the Keeling curve in a separate post soon.) Back to the question of extinctions and CO2. What is unknown is how quickly such a chain of events (high temperature and CO2 causing the hydrogen sulfide chemistry to take over the seas) could occur. 

When people talk about the extinctions of species, and how our environment is changing, sometimes they ask, "Do you think we could go extinct?" Until I read Ward's book, I would always dismiss that, not wanting to be an alarmist. Now I think differently, and look for a funny or tactful way to sidestep the question -- depending on the audience and the situation. 

For the truth is that of course we will go extinct -- the question is whether that occurs in billions of years, when our sun expands to the point of incinerating life on our planet, or due to some event MUCH sooner.  The connection that Peter has now illuminated, puts a very different timescale on the issue. There is a big difference between the possibility of a mass extinction during the next thousand years, or the next billion. As Ward explains, we can not yet predict how quickly high CO2 levels could change the ocean biochemistry system. 

Also it is still hard to project the rate of change for CO2, given the recent and current rapid growth of our emmissions, largely from energy production. Dr. James Hansen, a leading climate expert points out that at the current rate CO2 will increase 100 ppm in approximately 40 years. During past periods of abrupt change -- the most recent one occuring approximately 50 million years ago -- it took roughly a million years for CO2 to change by 100 ppm. Thus it is now changing about 25,000 times faster than at any time in known geologic history.

Unitl now, I thought the primary issues associated with climate change and increasing levels of CO2 were a) how much the CO2 and other greenhouse gases would warm the planet, b) how the warming would melt the ice sheets, causing a major crisis from sea level rise over the next few centuries, and c) the effect of CO2 disolving in the ocean, causing a drop in pH -- known as Ocean Acidification. With this new powerful insight from Dr. Ward,  I now add the CO2 itself as a threat even if the timeframe is some unknown number of centuries, or even millennia. 

If you are like me, you probably are stunned with this information, and may need to let it sink in. It truly puts a new level of importance on the issue of how high we are willing to let CO2 levels rise, regardless of the cost to solve the challenge, or the impact on short term economics. As they say, extinction is forever. Until now, I never seriously considered that there was even a remote possibility of humans going extinct for hundreds of thousands of years.

Now I see a different reality if we were to foolishly let CO2 levels climb ever upward. Of course at some point necessity and human ingenuity will likely figure out a way to reduce the CO2 levels, so-called "geo-engineering." The challenges, side effects, and unintended consequences of geo-engineering are ENORMOUS. We will look at that in another blog post.

Comments

All you need now is to show that the CO2 caused the mass extinctions rather than the mass extinction resulting in decaying life releasing CO2. Your graph show millions of years when CO2 levels were over 1000ppm with no mass extinctions. It appears that CO2 levels are inconsequential with regards to mass extinctions, since the mass extinctions occur across a huge range of CO2 concentrations. The graph actually suggests that CO2 rises as a result of an event that wipes out much of the life on the planet, unlocking carbon from sinks in the biosphere.

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That's interpretation, all that's really shown is a correlation.  You could just as easily say it shows that mass extinctions occur at spike tipping points of CO2 levels in the atmosphere.  The spike tipping points being too high in relativity to what the species of the time were accustomed to.  As we don't know and are rapidly on the way to find out it would be a safer bet to assume and prepare as if this were the case as opposed to your interpretation.  There's a nice documentary on the permian-triassic extinction event that actually links the high carbon levels to warming and releasing giant amounts of other greenhouse gasses into the atmosphere.  You can always say well we'll figure out a way to fix it, but will we? Assuming we can somehow find a way it'll likely be energy inefficient meaning we'll use massive amounts of oil... but wait peak oil is a real thing too.  Really leaves us in a dilemma, we have to act proactively not reactively, we can't assume we'll both find a way to combat it when it comes and that we will have the resources to undertake such meassures.

What an interesting and simple-minded proposition by Anonymous (who gets around quite a bit, it seems). For sure, mass extinction of all forms of life - plant and marine life included - would produce an increase in CO2. However, the proposal that "CO2 levels are inconsequential with regards to mass extinctions, since the mass extinctions occur across a huge range of CO2 concentrations" is completely fallacious and akin to proposing that the correlation of speed of motor car accidents with mortality in such accidents is 'inconsequential' as such deaths occur 'across a huge range' of speeds. No, moron, the point is that the huge majority of mass extinctions occur at CO2 levels above 1000ppm; similarly, most car accident mortality occurs at speeds over 40kmh with a change from 10 to 80% occurring between 50 and 70kmh. Interestingly, when not aided by a machine, the human body can propel itself only at speeds below 40kmh, consistent with the idea that we have evolved to be able to withstand our own self-inflicted damage... Establishing a causal link is what allows us to distinguish between correlation and causation. The sequence in this case is as follows - watch carefully; this isn't rocket science: CO2 increase -> ocean warming -> increased ocean acidity -> more algal blooms -> production of H2S -> lethal levels of H2S -> massive extinctions. There is some non-linearity in the sequence, too; more CO2 also means more ocean acidity, directly, and more CO2 also means more food for algae, etc. While it is impossible to prove causal links for past events, it is entirely possible to demonstrate each part of the sequence in the present, thus inferring the existence of the chain in the past. Personally, I'd prefer to have some idea of what is coming, based on the most developed approaches to predicting the future that I can find, rather than just stick my head in the sand and wait until reality comes and kicks me from the rear. If you prefer the latter, Anonymous, by all means, act in that fashion, but at least have the decency to absent yourself from rational discussion about our combined futures - leave that to those of us capable of the effort.

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