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2024-09-20 03:59:42 UTC
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PermalinkScientists have captured Earth's climate over the last 485 mn years.
Here's the surprising place we stand now.
WaPo, 20 Sep 2024 0:41Z
An effort to understand Earth's past climates uncovered a history of wild
temperature shifts and offered a warning on the consequences of
human-caused...
Study charts how Earth's global temperature has drastically changed over the
past 485 mn years, driven by CO2
Phys.org, 19 Sep 2024 18:18Z
The new curve reveals that temperature varied more greatly during the
Phanerozoic than previously thought. Over the eon, the GMST spanned
between 52 and 97 degrees Fahrenheit (11-36 degrees Celsius). Periods
of extreme heat were most often linked to elevated levels of the
greenhouse gas carbon dioxide in the atmosphere.
Earth's ancient `greenhouse' conditions were hotter than thought
Science News Magazine, 19 Sep 2024 18:17Z
This latest study used an interesting data fusion technique. Data
from the fossil record was used to inform essentially an AI/climate
model combination. The program learned by trial and error what the
climate looked like to have left the paleo data that's been collected
about the era from 500 to 250mya "just" before the rise of the dinosaurs.
Not too much directly remains of that bygone era. We can't find
samples of trapped 500 mya air like we can with 1 mya -- which can be
found down 4 km in Antarctic ice (i.e. near ground level), for
example. What we know about temperatures and even air composition
back then comes from what we understand should happen at different
levels of CO2 or temperature to various fossils e.g. those with
shells. But these so-called proxies are usually only good within a
factor of 2 or 10. One of the best ways to spot a hillbilly
pretending to be a scientist is they take such things literally --
like their bible. :)
So the idea is to use the fossil data, run a bit of climate
simulation, and try to figure what kind of remains the climate sim
says should be found in the relevant rocks or animal bodies. If you do
that over enough data then your climate sim and raw data work together
to get a result that is better than either. The same kind of methods
(Kalman filters etc) are used to filter inputs from the driver and the
modern motor vehicle in order to keep it on the road.
But the exercise for today is to try to reproduce the results without
having to make the heavy AI software that was used in the paper,
above. Can we cook up something simple that gets the same kind of
result, and what does it indicate about the world of 500m BC?
One of my go-to programs for this kind of work has been MacKay &
Khalil 1d sim (usu called "1drcm" but aka sometimes as OGMI) they
wrote back in '91. It simulates ~20 layers of the atm, make some
simplifying assumptions about the earth's orbit and rotation, allows
many many things to be tunable and allows different conditions to
change through its simulated years so you can see what happens when
e.g. CO2 doubles, other GHG change, or the planet loses all its ice.
On AGW we've looked at many of these over the years. Consult google
groups for the often bloody details.
Today we'll try to see what you need to tune up to get the surface
temp up to what the research found was among the warmest millennia
500mya. With current world temperatures averaging around 15C the
warmest this latest research found was 36C for the planet -- i.e.
21C warmer than "now" (usu taken as ~1950 in paleo studies). What do
you have to do to get a climate model to spit out a number like that?
Well first off we can ramp up the CO2. Like most molecules with more
than 2 atoms, the ability of 3+ atom molecules to "twist around" allows
them to interact with long-wave EM radiation. Molecules like O2 and N2
that make up most of the air can not do this. Most of the air is
transparent at infra-red (heat) wavelengths. But GHG -- a very long
list -- interact with IR photons. And the problem for civilization is,
when heat and GHG interact about 1/2 the photons get reflected back
down to earth where they came from. And this causes the earth's temp
to rise to try to get rid of the "extra" heat that it finds coming
down to say hello.
So we can ask the sim to ramp up the CO2 in steps. The program advises
users to allow ~1200 days of simulated time to allow the model to
settle after anything changes. 1200 days of simulated time take about 1
sec on a 20yo computer. :)
If we ignore the vast bulk of the output from 1drcm and just focus on
the surface temperatures it's predicting for "average global
temperature" we get this table:
CO2 surf temp
(ppmv) (deg K)
280 289.02219
310 289.29288
415 290.08521
560 290.92401
1000 292.64624
2000 294.86404
3000 296.22125
4000 297.20767
5000 297.98401
6000 298.62933
7000 299.18082
8000 299.64133
9000 300.11777
10000 300.51181
Scientists are used to thinking in degrees Kelvin, but most people
have trouble even with Celsius. So what we'll do here is use the
temperature at the start of the table as a baseline and subtract it
off. But keep in mind that "0" on this scale is roughly around 15C.
CO2 surf temp
(ppvm) (deg C rel ~1850 avgs)
280 0
310 0.27069
415 1.06302 <- we are supposedly here
560 1.90182 <- supposedly ~2100 AD
1000 3.62405
2000 5.84185
3000 7.19906
4000 8.18548
5000 8.96182
6000 9.60714
7000 10.1586
8000 10.6191
9000 11.0956
10000 11.4896
Well first off we see the model seems a tad conservative. NASA and
ESA have been talking the past couple years that the "1.5C level above
pre industrial temperatures" is close to being breached. In fact many
agencies claim we are right on that limit now and are taking side
trips to higher levels in some months. So it looks like the model
suggesting "now" should be around 1.1C higher than temps in the 1850s
is a bit low. We suspect more is going on that just CO2 ramping up.
The next thing to notice is the temperatures predicted for anytime
where CO2 levels are up to 10000 ppmv -- i.e. 35x times current levels
are normally considered "poisonous" in industrial settings -- seem very
cool. 11.5C above 1850s temps is way too low. Again, this suggests
more than CO2 increases probably need to be handled to replicate the
recent research.
So what can we do next? Well CO2 is not in isolation. "Most" gases in
the atm are GHGs (i.e. have 3+ molecules). The model handles water
vapor easily because that is temperature dependent. As the temp rises
the air can hold more water vapor. That increases the amount of
downward reflected heat happening, but that just follows a known law.
So 1drcm handles that for us.
But maybe what should be handled by us -- as CO2 rises all the other
GHG rise as well. We've seen the main ones -- methane and N2O
(laughing gas) as well as low-level ozone all go up. Other gases,
too. Some of these are a result of industrialized
agriculture. Worryingly, some are the result of warming and hint at
"feedback loops" that are already starting to play a big part of how
the climate is evolving.
We can guesstimate what will happen with the gases handled by 1drmc by
looking at how atm levels of methane (CH4) and N2O vary as if they
were predicted by the current level of CO2. We find both of these
gases are 90% or more explained simply by the current amount of CO2 in
the air. So we can re-run the sims again with ALL the gases going up
in accord with simple rules.
And we get:
280 0
310 0.29972
415 1.18207 <- now
560 2.1286
1000 4.1222
2000 6.75492
3000 8.39948
4000 9.61603 *** 500+ mn y ago
5000 10.5923 ***
6000 11.4045 ***
7000 12.1036 ***
8000 12.7541 ***
9000 13.2742 ***
10000 13.6228 ***
The surf temp has risen, but even the "now" number still seems too
small. None of the higher numbers is anywhere near 21C as published.
So what next?
Well one thing the newspapers don't talk about too much is the
"shininess" of the earth -- its albedo. There are several types but
it just means the% of light that is reflected by clouds and
ice. Clouds and ice reflect "most" light that comes in from the sun
before it has a change to become heat. Heat happens when light hits
the ground. The surface as we've seen is around 15C. And the science
of heat indicates that the kind of EM radiation coming off an object
depends mostly on its average temperature. And 15C corresponds with
infra-read. (The visible surface of the sun is around 5000K and that
radiation corresponds with light in the yellow/green part of the
spectrum).
So we could monkey around with the albedo in the 1drcm sim. E.g. we
could presume -- like many scientists have forecast for the past 30y
-- that at some point all free ice on earth will disappear. They say
this is nothing unusual, significant ice at the poles only started up
around 4 mn years back. For a long time before that earth was a
tropical hothouse with forests growing at N and S poles.
1drc handles the albedo of clouds itself. Again, this is related to
the amount of water vapor that can be held in the air at different
temperatures. As the temp goes up about 17% more H2O is held in the
air per extra deg C. The program handles that. It also handles the
area of the earth that has clouds. It normally average around 50%.
The program allows you to adjust that. But I'll go for the sea ice.
Without any sea ice -- expected in 2100 and maybe happening for a
couple of months by around 2050 -- the albedo of all the areas that
are not cloud, not ice, not snow, not bright sandy deserts -- all
that amounts to an albedo around 0.10. Making a little calculation and
just subtracting out the ~5% of the earth that is currently super
bright white ice shows we need to expect that 0.10 to reduce to 0.05
after the ice and snow melt.
So we can run add that in there as well. It'll do 2 things -- one that
assumes all the ice goes by 2050, and the other all the ice goes by
2100.
CO2 Av surf temp rel 1850
(ppmv) Noice 2100 Noice 2050
280 0 0
310 0.29972 0.29972
415 1.18207 1.18207
560 2.1286 5.06546
1000 7.08658 7.08658
2000 9.69892 9.69892
3000 11.3447 11.3447
4000 12.5695 12.5695
5000 13.5512 13.5512
6000 14.3913 14.3913
7000 15.0934 15.0934
8000 15.7148 15.7148
9000 16.3378 16.3378
10000 16.7117 16.7117
The difference is at least stark for the predictions for 2050. If we
assume by then atm CO2 will be 560 ppmv (given it's risen from 280 to
420 ppmv over the past 150y) but there *is* still seaice then global
temps -- according to 1drcm -- will avg around 2C above pre-industrial
levels. If we have no seaice then temps will be around 5C above
pre-industrial levels. In either case if by 2100 we have still been
pumping out CO2 from fossil fuels and all the products they now make
from it (coz just cant just burn it all in only 20% efficient engines,
can you?) and CO2 is near the 1000 ppmv level and there is no seaice
temps will be around 7C above pre-industrial levels.
But nowhere in the future poor old 1drcm can see is anything like 21C
above pre-industrial. The "worst" is can predict for e.g. 250 mn ya is
around 13C above pre-industrial levels.
5, 10, 15C about 1850 values all sound tame until you consider there
are all EXTREMELY LARGE values. It's calculated the so-called "Ice Age
Unit" (IAU) of 5C represents *in the past* the difference between the
top and bottom of a major glaciation. With all the normal icy parts of
the planet frozen and sea levels maybe 20m lower than now it is about
-5C cooler than the 1850s were. Still tame as far as the planet is
concerned, of course, because we've seen eras when sea levels were
100m lower than now.
The big question is -- how much of this can our cellphone loving
netflix streaming country club golfing lifestyles take? The pandemic
and supply chain problems now hint at "not much".
--
[It's Only About The Money!]
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Report
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The 10 largest food producers in the UK generate more greenhouse gas
emissions globally than the entire aviation industry, ...
[Humans == 40 Gt CO2/yr; volcanoes <0.1 Gt/yr].
Global carbon dioxide emission to the atmosphere by volcanoes
Volcanic CO2 presently represents only 0.22% of anthropogenic emissions but
may have contributed to significant "greenhouse" effects at times in Earth
history.
-- Science Direct
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