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General global warming / climate change discussion

11 Mar 2019 00:02

Watsisname wrote:
Source of the post You suggested previously that just because we don't see "short blips" of warming in the climate record does not mean they did not occur.

What I am showing is that short blips of greenhouse-forced warming cannot happen without being recorded, precisely because the effects of greenhouse gas emissions cannot be short lived.  If a lot of greenhouse gas is injected in the atmosphere rapidly, the result is many thousands of years of global climate change at least, which leaves behind clear evidence in the rocks.

In other words and very simply, we can be very sure there are not large rapid and brief warming episodes missing from the record.  Physics and geology don't work that way. :)

This was exactly my point, thank you for clarifying it for me Watsisname.
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midtskogen
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11 Mar 2019 01:38

Watsisname wrote:
Source of the post What I am showing is that short blips of greenhouse-forced warming cannot happen without being recorded, precisely because the effects of greenhouse gas emissions cannot be short lived. 

Ok. If PETM can serve as an example of change with a rate similar to or greater than we observe today, I don't need to go further, but I'm still curious about the absolute certainty of such events being recorded.  PETM occured relatively recent in Earth's history, so much of the crust still exists today.  Also, would such an event have been recorded if it happened during a snowball or waterworld period?  And PETM happened during a time of at least moderate CO2 levels - would it have been recorded if CO2 levels were very low and only a relatively small increase would suffice for rapid warming, and if the CO2 was released over a very short period of time and not sustained (a supervulcano eruption lasting a few years perhaps), could the oceans have absorbed nearly all in decades leaving a very weak signal in the rocks and sediments?  And there were no benthic foraminifera until 0.5 billion years ago, so before that evidence from a PETM like event would have to be from something else.  The point being, Earth's history is so long that to say that certain brief atmospheric changes cannot have happened without trace seems very bold.

Watsisname wrote:
Source of the post In other words and very simply, we can be very sure there are not large rapid and brief warming episodes missing from the record.

Greenhouse gas induced warming may last a long time, but you also need to exclude the possibility of rapid and brief warming episodes of any possible cause.
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General global warming / climate change discussion

15 Mar 2019 19:32

midtskogen wrote:
Source of the post PETM occured relatively recent in Earth's history, so much of the crust still exists today.  Also, would such an event have been recorded if it happened during a snowball or waterworld period?

I of course make no claims that the geologic record is a complete record of all of Earth history.  However, the geologic record is pretty complete up to several 100Mya, and the changes we are talking about here are global.  My point here again is that we can be very sure that the reason they are absent in the known record is not because they happened but were not recorded.  If they happen, the effects are obvious and recorded everywhere, because deposition processes depend on climate.

Such rapid change also cannot easily occur in a waterworld scenario.  A global ocean has very high thermal inertia.  A larger offset in energy balance would be compensated by faster overturning circulation to bring the warmth to deeper water.  Continents allow the global average temperature to warm faster because air over land can warm faster.  I'm pretty sure geologists exclude the possibility the Earth was totally ocean for at least as far back as 600Mya anyway, for which we have good knowledge of how the continents and coastlines have shifted around.

For a snowball earth, changes are similarly slow due to the high albedo.  A given change in greenhouse concentration has less effect because less energy is absorbed overall.  (It took a lot of greenhouse gas buildup over time to break out of the snowballs!)  Rapid warming might occur at the ends of snowballs, due to the dynamics for how the climate system breaks out of the snowball state (very high greenhouse gas concentration combined with ice-albedo feedback cycle working in overdrive).  But we don't know just how rapid the thaws were (as far as I know, this might bear looking up research on). :)
 
At any rate, if we have to go so far back as the snowballs to see similar magnitudes and rates of global change, I think that only emphasizes the point of how dramatic the change humans are causing now is.

midtskogen wrote:
Source of the post Greenhouse gas induced warming may last a long time, but you also need to exclude the possibility of rapid and brief warming episodes of any possible cause.


Watsisname wrote:
Besides greenhouse gas emissions like during the PETM or today, can anything warm the world this much this rapidly?  Probably no. 
  • Volcanoes cool the planet rather than warm it, and the effects go away within a few years.  Likewise with asteroid strikes.
  • The Sun can change its output rapidly, but when it does it is not by very much.  When it changes a lot, it does so very slowly.  
  • Earth's albedo may change, but not very quickly.  The fastest is probably during the ends of snowball earth episodes.
  • Earth's orbit and axial tilt change, but on well understood cycles with 10s to 100s of thousands of year periods.
  • Faster temperature change may be seen in Greenland ice core data, but these are not global rates.
 
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16 Mar 2019 11:31

The "fact" that triggered this discussion was that the global warming we see today is "no-where in Earth's history".  This is often repeated, and I think such claims ought to be questioned.  Can we really, really know this?  Since the geological record is not complete, and limited information is passed to the record anyway, it's also difficult to prove such claims wrong, but the burden of proof is on those presenting the "facts".

If we restrict the history during which Earth has had interesting life, we exclude 90% of Earth's history, but we know a lot more about these remaining 10%, so for that period it's at least possible to have an interesting discussion.  That there has been no global warming of 0.9 degrees over 150 years or so during the past 4-500 million years until our time still sounds like an incredible claim.  If we take the projected warming for granted, which starts at about 2 degrees over 250 years, well, I'd like to see the evidence that no such things can possibly have happened at the end of an ice age, for instance.  Some projections have 4-5 degrees of warming, but the "likely" range is wide and the upper figures can't be presented as a fact.

We've been fed so many claims about climate change from media over the past few decades that I think people, even smart people, have for the most part stopped questioning most of it if it sounds scary.  I just did a search in Norwegian newspapers for "because of climate change", and many 10 - 15 years old articles came up, and interestingly, many claims can now be confirmed or falsified because had predicted something by around today.  I could not find any claim that actually had happened, only things we now can safely say that did not.  There were many claims about the arctic summer ice, obviously, but also other claims like epidemics, food production and water shortages which never happened within the stated timeframe.

PETM is interesting, and that we see a mass extinction of benthic foraminifera in the fossil record, but considering that PETM happened when Earth already was very warm, and it took ocean temperatures to extreme levels (figures like 36C in the tropics and 23C in the arctic have been given), that there was an extinction event may not be that surprising.  But were a similar warming to take place when it's cooler, like in our ice age era, would there be mass extinctions or something else that absolutely would leave a clear mark in the fossil record?  It's difficult to prove that something happened millions of years ago, but often harder to prove that something couldn't have happened.
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16 Mar 2019 11:34

Watsisname wrote:
Source of the post For a snowball earth, changes are similarly slow due to the high albedo.  A given change in greenhouse concentration has less effect because less energy is absorbed overall.  (It took a lot of greenhouse gas buildup over time to break out of the snowballs!)  Rapid warming might occur at the ends of snowballs, due to the dynamics for how the climate system breaks out of the snowball state (very high greenhouse gas concentration combined with ice-albedo feedback cycle working in overdrive).  But we don't know just how rapid the thaws were (as far as I know, this might bear looking up research on).

Precisely, we don't know.  For that reason it's hard to rule out the possibilities.  If there were snowball events, we obviously got out of them, and it's not a stretch of imagination to consider very strong feedback effects when ice was replaced with open water considering the solar irradiation in the tropics.
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25 Mar 2019 00:58

midtskogen wrote:
The "fact" that triggered this discussion was that the global warming we see today is "no-where in Earth's history".  This is often repeated, and I think such claims ought to be questioned.  Can we really, really know this?  Since the geological record is not complete, and limited information is passed to the record anyway, it's also difficult to prove such claims wrong, but the burden of proof is on those presenting the "facts".

If we restrict the history during which Earth has had interesting life, we exclude 90% of Earth's history, but we know a lot more about these remaining 10%, so for that period it's at least possible to have an interesting discussion.  That there has been no global warming of 0.9 degrees over 150 years or so during the past 4-500 million years until our time still sounds like an incredible claim.  If we take the projected warming for granted, which starts at about 2 degrees over 250 years, well, I'd like to see the evidence that no such things can possibly have happened at the end of an ice age, for instance.  Some projections have 4-5 degrees of warming, but the "likely" range is wide and the upper figures can't be presented as a fact.

We've been fed so many claims about climate change from media over the past few decades that I think people, even smart people, have for the most part stopped questioning most of it if it sounds scary.  I just did a search in Norwegian newspapers for "because of climate change", and many 10 - 15 years old articles came up, and interestingly, many claims can now be confirmed or falsified because had predicted something by around today.  I could not find any claim that actually had happened, only things we now can safely say that did not.  There were many claims about the arctic summer ice, obviously, but also other claims like epidemics, food production and water shortages which never happened within the stated timeframe.

PETM is interesting, and that we see a mass extinction of benthic foraminifera in the fossil record, but considering that PETM happened when Earth already was very warm, and it took ocean temperatures to extreme levels (figures like 36C in the tropics and 23C in the arctic have been given), that there was an extinction event may not be that surprising.  But were a similar warming to take place when it's cooler, like in our ice age era, would there be mass extinctions or something else that absolutely would leave a clear mark in the fossil record?  It's difficult to prove that something happened millions of years ago, but often harder to prove that something couldn't have happened.

This is true, but it's also true that for most of the planet's history it was inhospitable to life.  Human-induced changes occur more quickly, so I think that is how they should be distinguished from changes that occurred before humans were here.

We should care about animals, because we are one of them, and something that negatively impacts them will negatively impact us.  Regardless, we have to curtail animal agriculture for a variety of reasons- health, environment, water shortages, land use issues, etc.

An interesting aside to the question of how much better we have it than previous generations is the fact that our diet has gotten worse, MUCH worse.  The consumption of processed food has negatively impacted the gut biome, things like artificial sweeteners, high fructose corn syrup, etc.  Studies have been done showing that the diet in other parts of the world where processed food is not consumed, actually have lower rates of cancer, diabetes, heart disease, obesity, depression, anxiety, etc.  The gut biome can actually turn on or turn off genes, thus increasing or decreasing the influence of heredity.
 
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25 Mar 2019 03:51

A-L-E-X wrote:
Source of the post it's also true that for most of the planet's history it was inhospitable to life.

Depends.  Life has been present for most of Earth's history, but complex life not so long.  Whether that's because Earth was inhospitable or because evolution needed all that time, doesn't seem clear.
A-L-E-X wrote:
Source of the post We should care about animals, because we are one of them, and something that negatively impacts them will negatively impact us. 

True.  Humans have changed several things, which impact animals, in a short time.  Amongst which climate is far from the greatest change.
A-L-E-X wrote:
Source of the post An interesting aside to the question of how much better we have it than previous generations is the fact that our diet has gotten worse, MUCH worse

I disagree.  In the western world perhaps slightly worse than the previous generation, but in general people today are healthier, parly because of improved diet.  A few generations back undernourishment was normal in most of the world.  Slightly unhealthy food is better than no food.  Increased rates of cancer, diabetes, heart diseases can be a sign of improved nourishment since these are all conditions that increase with age.  That is, people live longer, partly because of an improved diet.
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25 Mar 2019 05:26

I believe pollution, destroying rain forests and land use changes could be more impactful.  About the western world you are also correct, in the US in particular, for the first time, longevity has actually decreased.  Undernourishment was a much bigger problem a few generations ago, but now we have a different problem- obesity.  Western food has become much too processed which affects gut microbes and leads to a wide variety of ailments that have become much more common.  It's a problem that has an easy solution- increase consumption of fiber, raw fruits and vegetables, raw grains, legumes, etc.  Stop eating fast food, any type of soda (diet or otherwise) and the deceptive "low calorie" food that is of no nutritive benefit.  Eat more earlier in the day so your body has more time to digest food rather than late at night.  I was particularly intrigued to learn that our stomach has its own nervous system and it's like a second brain which can influence our moods and our gut bacteria can even influence which genes get turned on or off.

This is from the PBS show I was watching earlier:

http://pressroom.pbs.org/-/media/Images ... Final.ashx

http://webcache.googleusercontent.com/s ... clnk&gl=us

I also found this article which you might like regarding prior climate changes:


https://www.nature.com/articles/s41598-018-38089-y


https://www.nature.com/articles/s41598-018-38089-y

Almost 13,000 Years Ago, a Comet Impact Set Everything on Fire

Roughly 12,800 years ago, planet Earth went through a brief cold snap that was unrelated to any ice age. For years, there have been geologists that have argued that this period was caused by an airburst or meteor fragments (known as the Younger Dryas Impact Theory). This event is believed to have caused widespread destruction and the demise of the Clovis culture in North American.

This theory has remained controversial since it was first proposed. However, an international team of scientists recently discovered geological evidence in South America that could settle the debate. As the latest indication of an impact that took place during the Younger Dryas Boundary (YDB) period, this crater indicates that the effects of this event may have been more widespread than previously thought.

The paper which describes the team’s findings recently appeared in the journal Science Reports. The team was led by Chilean paleontologist Mario Pino and included multiple geologists from Chile and the United States, as well as James Kennett – the professor emeritus of geology at UC Santa Barbara. As they indicate in their study, this latest impact crater was found in the Osorno province in southern Chile.

https://www.universetoday.com/wp-conten ... 663.jpgNew research shows that some 12,800 years ago, an astonishing 10 percent of the Earth’s land surface, or about 10 million square kilometers, was consumed by fires. Credit: Pexels.com.

 

As Kennett noted in a recent article in The Current (a university press maintained by UCSB), the crater would have led to widespread destruction, characterized by biomass burning, megafaunal extinctions and global cooling. “It’s much more extreme than I ever thought when I started this work,” he said. “The more work that has been done, the more extreme it seems.”

The discovery was made possible by a Chilean group of scientists who were studying sediment layers at the well-know Quaternary paleontological and archaeological site, known as Pilauco Bajo. Years ago, these scientists recognized changes in the sediment record that were associated with the YDB impact event.

These included a “black mat” layer that coincides with the disappearance of South American megafauna fossils and human artifacts dated to the Pleistocene (12,800 years ago), indicating a severe shift in the climate. This was a major find since the vast majority of evidence for the YDB Impact has been found in the northern hemisphere.

This includes a previous discovery made by Kennett and another team of geologists, who uncovered a very young impact crater measuring 31 km (19.25 mi) in diameter beneath the Greenland ice sheet. As he explained, this latest discovery adds to the overall weight of evidence for the impact theory:

“We have identified the YDB layer at high latitudes in the Southern Hemisphere at near 41 degrees south, close to the tip of South America. This is a major expansion of the extent of the YDB event… Because the sequencing of these events looked like what had already been described in the YDB papers for North America and Western Europe, the group decided to run analyses of impact-related proxies in search of the YDB layer.”

Artistic rendition of the Chicxulub impactor striking ancient Earth, with Pterosaur observing. Credit: NASA

This analysis revealed the presence of microscopic tiny spheres (spherules) of minerals that were reasoned to have formed in the presence of extremely high temperatures. The layers containing these spherules also showed high concentrations of platinum, gold and iron particles that are rarely found in nature.

Even more surprising was the unusual presence of chromium, an element not found in any of the Northern Hemisphere YDB impact spherules. This coincides with what has been found in volcanic rocks sourced to the Andes, which indicates that the cometary objects associated with that impact must have hit in that part of South America as well.

Other evidence that Pino and his team considered had to do with indications of environmental disruption in South America that were dated to the same period. These included micro-charcoal and pollen samples in the impact layer that were indicative of a large biomass burning event – the largest that had been seen in thousands of years, in fact.

All of this indicates that there was an abrupt and major shift in the climate. However, unlike what occurred in the norther hemisphere, where the climate became suddenly cold and wet, conditions at Pilauco rapidly became warm and dry. An impact that took place in many spots across the globe would explain this “seesaw” effect between zonal climatic belts.

Artist’s impression of the Pleistocene era, showing woolly mammoth, cave lions eating a reindeer, tarpans, and woolly rhinoceros. Credit: Wikipedia Commons/Mauricio Antón

The speed at which this change took place is also best explained by an impact, rather than slower oceanic processes. An impact is also a more likely explanation for how large animals native to South America during the Pleistocene era – like giant ground sloths, sabretooth cats, mammoths and gomphotheres – went extinct.

It would also explain why fossilized samples of human bones and artifacts in the impact layer – which are similar to those attributed to the Clovis culture in Norther America – declined very suddenly. But as Kennett explained, the most impressive thing about this find is the distance between it and the closet well-studied site in South America – about 6,000 km (3730 mi) away – which greatly expands the extent of the YDB impact event:

“This is further evidence that the Younger Dryas climatic onset is an extreme global event, with major consequences on the animal life and the human life at the time. And this Pilauco section is consistent with that.”

Reconstructing the geological history of our planet is key to understanding how it evolved over time, and what effects this had on the evolution of life here on Earth. This knowledge has also come in handy in determining what effects humanity has been having on the planet in the most recent period – commonly dubbed the “Anthropocene” by geologists.

Further Reading: UCSB
 
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12 May 2019 01:28

I read an interesting article concerning sea level rise today.  In Norwegian, sorry.  It's known that if the Greenland ice sheet completely melts, the global sea level will rise by about 7 meters.  But in reality it's a bit complex.  Perhaps counter intuitive, as the ice sheet melts, the sea level around Greenland as far away as Scandinavia, the Canadian Atlantic and north-eastern US will drop, if anything.  By many meters some places.  The gravitational influence of the sheet is so great that it influences the geoid, i.e. the shape of the ocean surface changes more than the added water to the oceans in an area up to a couple thousand km around Greenland.  This effect is immediate.  The land rise caused by less push by the weight of the ice on the crust over the mantle is slow and will take several thousand years causing further sea level drop around Greenland.
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