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Comment by flyGuyOnTheSly | Hacker News Reader

Are CO2 levels higher than they were ~150m years ago when crabs first evolved into being?

The Jurassic had higher CO2 levels than today, but the rate of change in atmospheric CO2 was much, much slower than today.

To provide an analogy: Most folks are concerned about our acceleration, not our velocity. You can accelerate to 60mph slowly and comfortably, or you can accelerate to 60mph fast enough to kill you. It's not like 60mph is the problem, it's that if your biological systems don't have enough time to recover from the acceleration you will suffer consequences.

I think a another example to convey the message to the average person would be slowing down from 60mph. You can do so by pressing on the breaks or by slamming into a tree. Suddenly stopping by hitting a tree is something more people have indirect experience with than the idea of a speed increase strong enough to cause the same problems.

From https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at...

> There is evidence for high CO2 concentrations between 200 and 150 million years ago of over 3,000 ppm, and between 600 and 400 million years ago of over 6,000 ppm.

For comparison:

> Global annual mean CO2 concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century to 415 ppm as of May 2019. The present concentration is the highest for 14 million years.

> There is evidence for high CO2 concentrations between 200 and 150 million years ago of over 3,000 ppm,

And it didn't end up well, Permian-Triassic extinction event was the biggest mass extinction in history.

https://marinebiology.co/2015/04/10/greatest-mass-extinction...

These are fascinating facts. Thanks for digging this up. Does anyone know what the max rate of change around ~150m and ~500m years ago was? I reckon this information might not be available.

It's very hard to look back that far and compare to the measurements today because our rate of rise now is easily measured across years, whereas the data for millions of years ago is via the geological and fossil records, which records time on a longer scale. I recall that when they've modeled possible events which would sharply raise the C02 levels, it takes a very significant like the end of an ice age or huge amounts of volcanic activity.

From the fossil record we know that we last had something similar to the current levels about 15-20 million years ago, when our ancestors were just great apes. It was indeed a few degrees warmer and the sea level was higher. https://www.sciencedaily.com/releases/2009/10/091008152242.h...

We do have very good levels from the more recent history from ice cores, which shows that the current rate of change is unequalled: https://www.climate.gov/news-features/understanding-climate/...

Thank you so much for sharing.

Crabs didn't stop evolving. They're not the same crabs.

This is technically true, but it does not comprehend the threat. Crab populations (etc) can survive in a broad range of CO2 levels, but there is no reason to think that they can survive a rapid CO2 and acidity transition like the one that is underway right now. Corals are among the threatened organisms, and they can't migrate very quickly. Coral reefs, in turn, are a habitat for organisms like crabs (and 25% of marine species overall) and if they die off quickly, the underlying ecosystem is obviously under threat.

In other words: geological-scale change allows time for species and ecosystems to adapt and migrate. Rapid ecological change is correlated with loss of biomass, biodiversity, and species. The source of risk is not the CO2 level, but the rate at which it has changed.

No, they're lower.

But partial pressure of oxygen gas was also higher, and oxygen is highly alkaline.

From what I could find, oxygen is neither alkaline nor acidic. Bases and acids are ionic when dissolved in water, but O2 isn't.

There was some hand-waving going on, let me unpack it more fully.

Oxygen, the molecule, is apolar and un-ionized. Ozone is not. The amount of ozone in the atmosphere, hence dissolving into the oceans, is predicated on how much oxygen is present during lightning strikes, which is dictated by the partial pressure of oxygen.

More generally, oxygen is reactive, and contributes to reactions in an electron-donating capacity, what we call 'oxidizing' whether or not oxygen is involved. Alkalines are oxidizing, acids are reducing; if you add HCL to KOH, the H+ will reduce the OH-, or equivalently, the OH- will oxidize the H+.

The safest answer would have actually been: we can do some vague guessing about conditions 150 million years ago, but we certainly can't go back in time and measure it. The existence of crabs is proof that they could form shells under those conditions; what those conditions were, is guesswork.

Alkalinity and acidity are independent of whether a substance behaves as an oxidizer or reducing agent.

Nitric acid is an oxidizer. Hydroiodic acid is a reducing agent.

Lithium peroxide is an alkaline oxidizer. Lithium aluminum hydride is an alkaline reducing agent.

I should also point out that CO2 isn't acidic, either; that's the carbonate ion, which forms in solution.

Same deal with oxygen, except that reactivity between oxygen and water (but not oxygen and ozone) is much lower.

Doesn't matter. What does matter is the rate of change, and whether each species that makes up the ocean ecosystem can adapt fast enough to survive. Those that can't, go extinct. If enough of certain key species decline enough, the ocean ecosystem collapses, many more species go extinct, and around again.

The ocean will certainly recover in a few thousand years, or at worst a million. Human civilization's immediate prospects are less optimistic.

After a worldwide collapse of civilization, and forced population reduction below two billion, civilization will also begin to recover, and take maybe a century or three to get back to, say, the level of launching satellites. Global thermonuclear war could be expected postpone recovery to the upper end of the range.

After the end-Permian extinction (the worst mass extinction in the Earth's history), life took several million years to recover. From Wikipedia:

> Research indicates that recovery did not begin until the start of the mid-Triassic, 4 to 6 million years after the extinction;[73] and some writers estimate that the recovery was not complete until 30 Ma after the P–Tr extinction, i.e. in the late Triassic.[8]

The current extinction might not be as severe, but "a few thousand years" sounds really optimistic.

The P-Tr extinction was overwhelmingly worse than we are capable of, even on our worst day. It drove every single obligate-shelled ocean species to extinction. The ones with shells that came after were descended from those that had lost their shells, and then evolved them again.

If civilization collapses, the sudden pulse of reforestation and radical reduction in CO2 production will clear the excess in a few decades. Many shelled species will survive just by waiting it out; do you recall the 400-year-old clam that turned up recently? It is mostly the larval forms at risk.

The problem with civilization recovery is that the warming won't stop after it goes past some key thresholds. The positive feedback effects will keep pushing temperatures higher, and the CO2 already in the atmosphere will stay up there for thousands of years.

In that scenario civilization will have a very difficult time recovering, especially considering the massive disruption to agriculture.

“. . . the level of launching satellites.”

Not with all the easily accessible hydrocarbons gone it won’t.

You can make a rocket with ethanol.

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