Post by RonOPost by RonOWe are putting out a lot of carbon dioxide into the atmosphere.
Some people worry about methane, but the effect is likely
negligible because methane doesn't last very long in the atmosphere.
They are right to worry. The effect of CH4 is about .5 Watts per
square meter as compared to pre-industrial times. Crudely speaking,
this accounts for about a quarter of a degree of warming.
Why is it so? Well, the mean lifetime of CH4 in the atmosphere is
not that short, being about 11 years. As it is far more effective
at absorbing IR than CO2 it can add a lot of heat before it is gone.
When it does break down, some of it becomes stratospheric water
vapour, which is an excellent greenhouse gas itself. And this
effect lasts.
The effect of a unit of methane put into the atmosphere, over a
century, is still larger than that of a unit of CO2, though the CH4
will be long gone at the end of that period.
It's short lifetime hasn't stopped us from increasing the amount in
the atmosphere. CO2 levels have not yet doubled from pre-industrial
times, but CH4 is up 160%.
Finally, the bio-geochemistry of CH4 works against us. As the world
warms, microbes more actively devour our stock of sequestered
organic carbon, producing more CH4 and CO2. Arctic soils, in
particular, hold vast amounts of frozen organic matter - far more
than tropical soils. Field experiments have shown that the rate at
which arctic areas are giving off greenhouse gases is increasing.
This positive feedback could grow very nasty indeed.
We likely did
Post by RonOaccelerate global warming with our increased output of carbon
dioxide, but we did it at a time when global temperatures had
already been increasing for thousands of years.
Time scales matter.
The earth has warmed about 4C since the last glacial maximum about
20k years ago, most of that in the first 10k. We have now warmed
the earth one degree C in less than two centuries. And eight
billion of us depend on the ecosystems which were well adjusted to
that earlier climate.
It appears that already forests in parts of the world are no longer
stable ecosystems. Many will be replaced by more fire-resistant
(and less useful) trees, or by grass or scrub. And that's just the
beginning.
Post by RonOWe need to better define what the crisis is.
We probably should be nearing the end of the current warming
period. For the last million years we have had the 100,000 year ice
age cycles. The earth has been cooling for the last 3 million
years, but for the last million we went to a cycle of around a
hundred thousand years of cold interspersed with 20 to 30 thousand
years of warmer climate. The temperatures of the cycles seem to
have become more extreme in the last 500,000 years. The last warm
period got warmer than it is now, and more ice melted and sea
levels were 20 meters higher than they are now.
Eemian warmth was different. At this time the orbital eccentricity
was more than double the current value. With perihelion occurring
in summer, this led to strong increases in summer temperatures,
decreases in winter. The obliquity was also larger, meaning more
heat in higher latitudes.
The problem is that our temperature proxies are mostly summer ones -
winter does not leave us a lot of records. Tropical records can also
be difficult to work with, so there is a bias towards temperate and
polar records. Eemian warmth is mainly summer warmth, and not
directly comparable to our little experiment which will be
year-round warmth, with a bias towards winter and higher latitudes.
And, once more, the Eemian world did not have to support eight billion
people.
We
Post by RonOhave not reached that point, yet in this cycle, so things are not
yet as bad as they got without human industrial interference.
There was an article put up on TO, maybe a decade ago, that claimed
that the current carbon dioxide levels could prevent a recession
into another ice age.
As one of the authors of such a paper, I have to disagree with your
interpretation.
We might delay the next ice age. This really doesn't seem to
Nor would it be good. Ice ages begin very slowly in human terms.
If we still are an industrial society when the next one comes along
- some time in the next twenty thousand years - we will be able to
deal with it.
Worrying about a future ice age at this point is equivalent to
Julius Caesar worrying about world war II.
We got a taste of what things would be like when
Post by RonOtemperatures fell for the mini ice age that started in the 1300's
and didn't end until the start of the industrial revolution that is
supposed to be responsible for our current global warming.
The little ice age ended well before CO2 from industry became a
significant factor in climate. It has been shown that stratospheric
aerosols caused by increased volcanism account for about 60% of the
little ice age cooling. Given the noisy data, that's about as good
as can expect, though solar, GHG and land-use effects were also
accounted for.
The earth has seen
Post by RonOwarmer climates that had more ice melting and sea levels rising to
the levels that they claim may occur this time, but they obviously
happened before. So the regions that will be flooded will just be
a repeat of what happened last time a hundred thousand years ago.
You are drawing parallels where there are no parallels. See above.
William Hyde
It looks like you didn't comment relevantly on that topic, just
denied it with no discussion.
Really? You started with the claim that methane is not an important
greenhouse gas, and I went into some detail to show that it in fact is.
Then you went on to speculate that global warming might save us from
an oncoming ice age, and I reminded you that while an ice age is
coming soon in geological time, it is very far away in human time,
while damage from global warming is not.
I didn't say it would save us. I just said that the prediction was that
we might skip it, and that would be worse for the Arctic biology. It
would keep our crops from failing and our Northern cities from being
covered by a mile of ice, but as you say that would take thousands of
years. Skipping the next cold period would mean that there would be no
expansion of habitat for the arctic species that are now suffering a
decrease in habitat during the warm period.
Ok, then.
I did not mention ocean acidification, another consequence of our
atmospheric pollution. I gather from biologists that this is also
rather important.
So you dismissed it because it is in our distant future.
Failing to mention something is not the equivalent of dismissing it.
Particularly as I did bring it up in my second post. It is a real
problem, and one that won't be dealt with by geoengineering, which seems
to be getting to be a more popular idea in some circles.
Also, I don't think that ocean acidifcation is a problem for the distant
future. It is a problem now.
Why shouldn't
we consider it? The future is the future. Shouldn't you consider it
when thinking about doing something now?
We very much should.
Perspective is that it got
warmer last warm period and more ice melted than has melted at this
time. More permafrost was defrosted than now. The bad things that they
are predicting happened last time, but you claim that it was different,
but that doesn't change the fact that they happened last time.
For whatever reason the cold periods have gotten longer, and the
temperature shifts have become more extreme. Carbon dioxide is warming
up the planet, but the last look at it claims that it isn't as bad as we
think.
https://en.wikipedia.org/wiki/Quaternary_glaciation
Look at the graph of the Vostok station ice core data. Maybe we were not
destined to get as warm as the last few warm periods.
Old news. The orbital parameters we have had over this interglacial are
not as favourable for hot summers as in some past interglacials. As I
mentioned above, the eccentricity is now only about half that of the
Eemian, and larger eccentricity leads to more extreme seasons in high
latitudes.
One previous interglacial, known as isotope stage eleven, was also
anomalous. It had an orbital configuration much like the current one,
though that does not prove that the "stage eleven problem" was entirely
an orbital event. But it is indicative.
Two of the last 4
warm periods have gotten hotter than the current warm interval, but our
warm cycle seems to have faltered, and it looks like we should be in a
downward trend at this time, but something has kept that from happening.
The 4 previous warm period were warmer than it is now. Our temperature
seems to have peaked several thousand years ago for this cycle.
If you click on the Vostok link in the figure legend you can get the
methane numbers and for some reason this warm period is messed up. When
things got hotter last warm period methane levels peaked higher, but
dropped when the temperature started to fall. More ice melted than now,
and more permafrost thawed out, but the falling temperatures seem to
stop that even as CO2 levels remained relatively high. This cycle seems
to have been different even before we started pumping CO2 into the
atmosphere.
It sort of looks like we have already skipped the usual rapid
temperature downturn, and for some reason this cycle has maintained
higher temperatures for a longer period of time and it started long
before our CO2 intervention.
One idea is the "early Anthropocene" hypothesis:
https://en.wikipedia.org/wiki/Early_anthropocene
Basically the idea is that early agriculture made a sufficient change to
various greenhouse gases to have altered the climate slightly. As the
article notes, this is contested. I have seen Ruddiman's plot of the
concentration of various biogenic greenhouse gases over time for the
past few interglacials, and this one does stand out as different. Just
why this is so is another question.
As an orbit guy, I tend to blame the orbit for a lot of things (as you
will have noted) and when the timescales are too small for that,
volcanoes. But Ruddiman's idea is interesting, even if it isn't the
whole story.
The paper that was put up on TO did predict that
Post by RonOwe might skip the next ice age.
Actually this is not a new idea. I first saw reference to in in an
Asimov essay in the 1960s, discussing Milankovitch theory. It also
appears in a book I've recommended here many times, "Ice Ages -
solving the Mystery", by Imbrie and Imbrie, published some time in the
mid 70s.
Indeed,there was an SF novel circa 1990 which had a new ice age caused
by people following those crazy environmentalists. Another SF writer,
George Turner, had the same idea, but played it more subtly (the novel
titles are "Fallen Angels" and "The Sea and the Summer" - also titled
"The Drowning Towers".)
It seems to have been a first for a scientific publication. As far as I
know it was the first such publication since the turn of the century.
Everyone had just been worried about global warming.
As I keep telling you, the idea that we might miss the next excursion to
a full-blown ice age is old news. If that were the conclusion of our
paper, and only that, it wouldn't have been worth publishing. Certainly
not in Nature.
The idea is mentioned in a volume of Quaternary Research published in
1970, when it wasn't yet clear which effect was going to dominate,
cooling from stratospheric aerosols or warming from greenhouse gases.
Our paper used a coupled climate-ice-sheet model to examine the question
of future climate. Can you recall anything about the other paper, if
indeed it existed? Did it use a general circulation model?
I recall the paper was published a
Post by RonOcouple years before the Top Six were put out so that would be around
2015.
"Transient nature of late Pleistocene climate variability", Thomas J.
Crowley & William T. Hyde
Nature volume 456, pages 226–230 (2008)
It was mentioned in this group a few years later.
The next ice age wasn't the real point of the paper, which talked
about a larger and more significant change which might occur in the
next 50,000 years.
The Vostok data indicates that the last two cold periods had warming
cycles after the initial temperature crash. It got very cold, but then
warmed up again in a sort of roller coaster ride, but it looks like it
is just more noticeable than the previous temperature fluctuations.
The paper that I recall had a Science news article about it, and it was
the news article that noted something that was just mentioned in the
discussion of the paper.
I haven't heard much about it since. You may have written
Post by RonOsomething similar, but didn't come to the same conclusion.
Of course we did. And we knew it would be abused by the denialist
community, as it immediately was.
I've been involved in three papers which had as their point that some
of the worst case scenarios for GW might not happen, and in each case
some in the denialist community claimed that we had "proven" that
climate change was not a problem at all. Those who deal with
creationists will not be surprised.
Putting off the next ice age is about as urgent as dealing with the
flu season in 6629. Climate change is a problem now, not thousands of
years in the future.
Doesn't the Vostok data look like the next cold period has already been
put on hold? Based on previous warm periods we should already be
declining in temperature,
My co-author on the above paper, Tom Crowley, commented that we had
"missed the off ramp" for the next glacial cycle.
We are most likely to move from an interglacial to a glacial when
aphelion is in summer, from a northern hemisphere perspective. This
results in cool summers with less melting of winter snow. Next season,
snow may fall on existing snow, a prerequisite for building an ice sheet.
As aphelion is now in early July we have passed the most favourable time
for ice sheet formation, and obliquity changes are not favourable, thus
Tom's comment (IIRC he thought the most favourable time was about 800
years ago).
and the decline should have started around
10,000 years ago. What would the temperature be now if it had risen and
fallen at the same rate that it has for the last half million years?
If we achieve a stable climate, and the natural progression of the ice
ages kicks in, we will be easily able to deal with it. Assuming we
are at at least the current level of technical ability, that is.
You are going to stop Manhattan from being scraped down to bedrock by a
mile thick ice sheet.
You have to stop it long before then. At its inception an ice age is
easy to stop. By the time the ice sheet is a mile thick over northern
Canada, it's a much tougher job.
Would that be ethical? Shouldn't we be more
worried about making sure that the tundra gets established further
South. What ice age megafauna that we have left will be frolicking from
New Mexico across the great plains. They would be having the time of
their existence, but our crops would have been failing for thousands of
years before that.
I will leave the philosophy of it to you. I suspect that our
successors, assuming that Manhattan and agriculture are still important
to them, will have no qualms. But then, perhaps we won't survive to
that time without a hypersensitive ethical system.
It was
Post by RonOlikely that before that paper was published, no group had made a
similar prediction, since I did not recall any such previous prediction.
If just as much ice melts as melted last time, why wouldn't sea
levels reach the same depths? Sea level was 20 meters higher than it
is now,
That is off by a factor of two or three, probably due to an imperial
to metric switch. But it doesn't matter.
Again you say it doesn't matter. Why doesn't it matter?
What does not matter is your mistake as to sea level. Your point is
unaffected whether the Eemian sea level was five or twenty meters higher
than it now is.
Rising sea level itself does of course matter. More now than then, for
our species anyway.
The islands
that they claim are going to flood did flood back then and life on those
islands did become extinct. There was an article put up on TO where a
flightless Rail had reevolved on an island that flooded during the last
warm period and wiped out that previous flightless Rail species. It
would seem to matter.
It is the global warming doom sayer articles that are claiming that
there is going to be a 20 meter rise in sea levels, they may be talking
about 20 feet.
I recall one global map of projected temperature changes by 2100 which
had been based on data given in Fahrenheit degrees. Someone assumed it
was given in Celsius, so multiplied it by 1.8. Someone else assumed
that the new data set was still in C, and multiplied it again by 1.8
before plotting it. I think that the resulting map "predicted" warming
of 12F for parts of the US. Given that errors never die, this map is
probably still available somewhere and someone is uncritically using it
as a source.
Reminds me of the passenger jet that had to land on empty tanks in
Gimli, Man, because of a fueling mixup between gallons and litres.
Wiki claims that sea levels were 20 to 30 feet higher in
the last warm period than today.
Yes, but there is no parallel between the two cases. We probably can
halt this with far less than twenty feet of sea level rise. Or, though
I doubt it, thirty feet could already be baked in.
Or we could let it go much, much, higher.
William Hyde