
UVB radiation was the Devonian-Carboniferous extinction kill mechanism - nosianu
https://advances.sciencemag.org/content/6/22/eaba0768
======
labster
> Hence, ozone loss during rapid warming is an inherent Earth system process
> with the unavoidable conclusion that we should be alert for such an
> eventuality in the future warming world.

Did not know this worrisome hypothesis. The idea that a warming world could
inject more reactive material into the stratosphere via convective storms
seems reasonable. Thanks a lot for one more reason not to sleep tonight.

~~~
ChuckMcM
Hence the larger conversation around becoming multi-planetary as a species
being a survival mechanism.

~~~
sandworm101
Fixing the ozone layer is far easier than moving a substantial of the earth's
population off-planet. The total amount of gas is not extreme, which makes it
so delicate but also means that we may be able to artificially manage it.

~~~
ChuckMcM
I'm not sure what you are saying here. What this paper is saying is that at
some point the planet (before homo sapiens) had an "event" of some sort that
basically removed the ozone layer and killed off most of what was living on
the surface.

People don't have a mechanism to "inject ozone" into the stratosphere (we
count on the Sun to do that) so if it were removed again, we would all likely
die.

Similarly, at least one extinction event was due to volcanism, another thing
we puny humans have no means to control (as much as I would love to be able
to).

It is not disloyal to the global warming cause to acknowledge that there are
things that we _aren 't_ responsible for that could kill us too.

~~~
jecel
Even if the Earth loses all its ozone we would still be more protected here
than anywhere else in the Solar System. So any solution you come up with for,
for example, living on Mars would work here as well and be cheaper. If you
live in shelters covered in 2 meters of dirt on Mars, you could do that here
too and not have to generate oxygen to breath.

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avancemos
This is not a high profile paper. The accompanying domain to this post is
(unintentionally) misleading: the actual journal that this paper is published
in is ’Science Advances’, not ’Science’ (the prestigious one).

I thought there was something funny about the abstract...most abstracts in
high profile journals have a much different tone.

~~~
sradman
The underlying dataset is fascinating and supports the UV-B damage hypothesis
while also falsifying the mega-volcano hypothesis. It took a great deal of
Wikipedia research for me to get a feel for the paleo geography and paleo
climate of East Greenland 359 Mya. The “warming causes ozone collapse” meme
seems aimed at gaining media attention but that tactic seems to be the norm
now in scientific papers.

Sometimes the curation role of a journal is important and peer review can
identify errors. In this case it seems like access to the right geological
formations by competent scientists is key and I read nothing in the paper made
me question the science. I don’t think the lack of journal prestige diminishes
the significance of this specific paper; it probably reflects the modern
relevance of this extinction event.

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sneak
Context for those of you (like me) who aren't geologists and don't know of any
historic extinction events other than the k-t (66 Mya):

[https://en.wikipedia.org/wiki/Late_Devonian_extinction](https://en.wikipedia.org/wiki/Late_Devonian_extinction)
(376–360 Mya)

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MattGaiser
I didn't see a temperature for when this might become a problem. Does anyone
have that?

~~~
rrmm
[https://science.sciencemag.org/content/337/6096/835/tab-
pdf](https://science.sciencemag.org/content/337/6096/835/tab-pdf)

That's the ref in the paper. It's a bit confusing because they're looking at
chemical processes taking place at 15-20km altitude. Temps there are around
-55C maybe, 200K).

They plot changes for activation of the process, but I don't have enough
knowledge about it to understand the implications. The bottom axis of their
graph runs from 195K - 210K though so clearly it's not a big delta. They seem
much more interested in the amount of water vapor at altitude.

The other thing is that it seems like the process has a fairly short cycle
time. By which I mean they mention changes on the order of days. When I think
about ozone holes I think mainly in the context of decades.

So I'm not sure how much the mention of warming and ozone loss in the OP paper
was a 'hey that might be of note,' or was a more substantially linked
relationship.

(I kind of wonder if pole reversal/magnetic field weakening or solar events
could play into the loss of ozone during the extinction in the original
paper?)

The paper makes this statement at the end:

Last, we emphasize that because chlorine ac- tivation depends exponentially on
water vapor and temperature, and in turn that the forcing of climate may well
control the convective injec- tion of water into the lower stratosphere, the
idea that ozone “recovery” is in sight because we have controlled
chlorofluorocarbons and halon release is a potential misjudgment.

~~~
rrmm
Ok so I think the parameter you want to be looking for is the temperature (not
necessarily at altitude) that results in some particular amount (ppmv) of
water vapor at altitude. With the understanding that the hotter it is at
altitude the worse the mechanism is for ozone.

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colechristensen
I'm wondering how modern species would be differently vulnerable to a similar
UV challenge. The paper specifies the evidence they found and a mechanism
being DNA corruption in plant spores which were very exposed – well today most
of those plants (like all sorts of ferns) are extinct and replaced by
flowering plants with their much hardier seeds.

~~~
Freestyler_3
seeds or spores are they interchangeable?

I thought spores are like sperm, they are needed to produce seeds... or am I
wrong?

~~~
colechristensen
Not at all interchangeable.

The lifecycle of ferns is a bit exotic and familiar.

It's classified as alternating between two generations, the one which produces
the familiar large plant, and one that produces tiny plants.

It's something like "sexual reproduction with extra steps".

The fern chops its genome in half and produces spores with these haploid
genetics. The spores grow into tiny plants (< 1 cm) which grow leaves and
roots and then produce the sperm and/or eggs (the sperm actually swims to the
egg!) which fertilized, grow into a new familiar fern.

In flowering plants, seeds are the result of fertilization which happens in
the plant, they're bigger, contain food, and protective shells. The living
cells which carry life are hidden inside. Pollen is a bit like a spore in that
it's tiny and contains haploid genes, but still I'm guessing that process of
reproduction is considerably more durable to increased UV.

------
rrmm
Oh hey, another bad thing to worry about happening in 2020.

But it's a cool paper. It would be interesting to see if they can find more
instances of this sort of damage over various, widely space geographic areas.
And especially in other species/other external signs of UV damage.

Even though they do analysis to try to eliminate other possible explanations,
I'm not sure I'm super on board with immediately accepting the UV/ozone
explanation whole sale. I always like to see bets hedged with "lends further
evidence to support...." language.

I'd also love to hear from anyone with domain knowledge that might be able to
add their perspective on the paper.

~~~
londons_explore
I have searched for, but been unable to find, a chart of estimated UV levels
at ground level over the past few hundred years.

I'm interested in it because suntans seem so much worse now than in the past,
where people didn't have access to suncream, yet still spent lots of time
outside.

"I got used to it by spending my whole life outside" doesn't seem to fully
explain it.

~~~
rrmm
I don't know if they even have that data for that length of time. You might
find some info in literature regarding the difference in UV exposure in areas
under the ozone hole vs areas of more normal exposure.

As an aside, don't get misled by nutters talking about ground level UVC
levels. They don't know what they're talking about and are citing people who
don't know how to use their UV-C meters (which are sensitive at wavelengths
other than UVC and therefore require extensive filtering).

Further edit: I should mention total solar irradiance has remained relatively
consistent over time (and continues to). I bring up these things because I've
talked to some nutty people about this stuff in the past and those are common
stepping off points into la-la land.

~~~
kaybe
>I should mention total solar irradiance has remained relatively consistent
over time (and continues to).

It should be noted that the 11-year solar cycle is much stronger in the
shorter wavelengths, especially below 200nm. Since that is absorbed in the
ozone layer there is a change of up to 2K max in the stratopause (~50km). It
doesn't really appear to propagate down, and is rather on the level of a
scientific curiosity, but still. [0] (Longer-term changes than the 11-year
oscillation seem to be much lower, but this is hard to determine.)

[0]
[https://pubs.giss.nasa.gov/abs/gr08900n.html](https://pubs.giss.nasa.gov/abs/gr08900n.html)

To the parent post:

If you want to have information about UV at ground level you can look at proxy
data. [1][2][3] Of course there are some complications with that as always
though, and it's not that easy to interpret. But it looks like while there is
variation it is mainly along the 11-year cycle. (I can't say much about the
strength of the change on ground level without further reading. It's in the
low percent range on top of the atmosphere, but almost all of that will be
stopped in the ozone layer.)

[1]
[https://pubs.rsc.org/en/content/articlelanding/2009/PP/b9045...](https://pubs.rsc.org/en/content/articlelanding/2009/PP/b904515e#!divAbstract)

[2]
[https://www.tandfonline.com/doi/abs/10.1080/0143116050007705...](https://www.tandfonline.com/doi/abs/10.1080/01431160500077051)

[3]
[https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-...](https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.2011.03815.x)

Considering the issue of suntans, I think looking at the clothes people wear
is more relevant to the question to be honest.

~~~
rrmm
Thanks for the info.

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01100011
Hopefully this time we'll be able to geoengineer our way out of it. I would
think pumping out tons of ozone is significantly easier than removing
atmospheric CO2 or, you know, burning less carbon(how absurd, right?).

~~~
adrianN
Anybody can make Ozone, but how do you propose getting it high enough in the
atmosphere?

~~~
jojobas
1) Advance solar cell technology a little bit more

2) Make a Solar Impulse kind of planes that basically deposit excess power in
sparkgaps

3) Ozone

I suspect the ozone layer is not our biggest problem with the warming though.

~~~
namibj
Oh, we can already build planes that use high-efficiency propellers (with
efficient and lightweight gear-less axial flux motors) and soar above the
clouds 24/7, using height instead of batteries and ultra-light back-ground
solar cells laminated into a giant flying wing (or at least much more wing
than fuselage, because the motors should be distributed to reduce demands on
wing stiffness). A weight of less than 2.5kg/m^2 in the wing should be
feasible with large, monolithic carbon fiber sections, joined by narrow engine
segments. Overall it should be possible to stay below a wing loading of
5kg/m^2, so a 100m span, 1m chord 500kg plane gets about 18h out of 10km
height, see [https://www.rcgroups.com/forums/showthread.php?2601411-Is-
wi...](https://www.rcgroups.com/forums/showthread.php?2601411-Is-wing-loading-
what-determines-the-minimum-sink-rate-of-a-glider) .

