RonO wrote:
On 4/24/2024 7:23 PM, William Hyde wrote:
RonO wrote:
On 4/7/2024 5:55 PM, William Hyde wrote:
RonO wrote:
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We 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.
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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.
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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.
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When it does break down, some of it becomes stratospheric water vapour, which is an excellent greenhouse gas itself. And this effect lasts.
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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.
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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%.
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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.
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We likely did
accelerate 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.
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Time scales matter.
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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.
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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.
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We need to better define what the crisis is.
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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.
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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.
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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.
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And, once more, the Eemian world did not have to support eight billion
people.
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We
have not reached that point, yet in this cycle, so things are not yet as bad as they got without human industrial interference.
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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.
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As one of the authors of such a paper, I have to disagree with your interpretation.
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We might delay the next ice age. This really doesn't seem to
be that bad.
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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.
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Worrying about a future ice age at this point is equivalent to Julius Caesar worrying about world war II.
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We got a taste of what things would be like when
temperatures 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.
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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.
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The earth has seen
warmer 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.
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You are drawing parallels where there are no parallels. See above.
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William Hyde
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It looks like you didn't comment relevantly on that topic, just denied it with no discussion.
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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.
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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.
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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_anthropoceneBasically 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.
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The paper that was put up on TO did predict that
we might skip the next ice age.
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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.
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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?
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I recall the paper was published a
couple years before the Top Six were put out so that would be around 2015.
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Our paper was:
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"Transient nature of late Pleistocene climate variability", Thomas J. Crowley & William T. Hyde
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Nature volume 456, pages 226–230 (2008)
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It was mentioned in this group a few years later.
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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.
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I haven't heard much about it since. You may have written
something similar, but didn't come to the same conclusion.
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Of course we did. And we knew it would be abused by the denialist community, as it immediately was.
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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.
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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?
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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.
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It was
likely that before that paper was published, no group had made a similar prediction, since I did not recall any such previous prediction.
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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,
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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
What is YOUR view?
Re: What is YOUR view?
