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Absolute Worst Case Scenario?

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Call me paranoid but the rapid increase in greenhouse gases along with the rapid increase in global temperatures over the last 30 years but even more so over the last 6 years has now got me seriously contemplating, just what would the absolute worst case scenario be from Anthropogenic Global Warming?

 

If us humans become so greedy and/or energy thirsty that every molecule of greenhouse gas (such as carbon dioxide, methane and water vapour) gets lofted into the atmosphere whether it's via deliberate means such as drilling and mining for fossil fuels and then burning 'em, and deliberate burning/clearing of the rainforests and other forests, or/and "accidental" means such as positive feedback mechanisms to the initial AGW such as "natural" rain forest/other forest fires, rainforest/other forest death from heat stress, heat loving bacteria breaking down organic matter, increased water vapour (also a very powerful greenhouse) from warming rivers, seas and oceans, methane (also a very powerful greenhouse gas) released by melting permafrost and ice sheets and the Clathrate (aka Methane Hydrates) Gun mechanism, just how hot will Earth become?

 

Will Earth become as hot or even hotter than Venus with average global temperatures of 400C through 500C?  Could Earth singlehandedly due to us mere humans become not just the hottest planet in the universe but extremely hot with average global temperatures in the 500C through 1000C range?  Theoretically if virtually the whole troposphere averages much above 100C (the boiling point of water), then such extreme greenhouse heating would be virtually permanent because every molecule of water from the land and oceans will be permanently lofted into the atmosphere as water vapour and remain so since the air will be "too hot" for clouds and rain to form and wash it out.

Edited by Craig Evans
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No doubt the planet will warm and one day cool as we enter cycles... we are going through a warmer period so it is to be expected the warming is just a little unprecedented, some parts of the globe are experience a cooling too, such as parts of Antartica. We live in a world of balance as long as we have the rainforests being the 'green lungs' & seas acting as 'carbon sinks' I see nothing at all sinister. We need greenhouse gases without them, the planet would be in the freezer and life would not be possible. Green energy sector is growing with the price of oil at very low levels - this is perfect time to launch broadscale. Birth rates are dropping globally particulary developed nations, this can only be a good thing, in places like Singapore they're getting worried by the lack of workers, and ever growing ageing population, which our country is also following. Media just goes OTT. In hope to create fear, thus gain attention.

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Call me paranoid but the rapid increase in greenhouse gases along with the rapid increase in global temperatures over the last 30 years but even more so over the last 6 years has now got me seriously contemplating, just what would the absolute worst case scenario be from Anthropogenic Global Warming?

 

If us humans become so greedy and/or energy thirsty that every molecule of greenhouse gas (such as carbon dioxide, methane and water vapour) gets lofted into the atmosphere whether it's via deliberate means such as drilling and mining for fossil fuels and then burning 'em, and deliberate burning/clearing of the rainforests and other forests, or/and "accidental" means such as positive feedback mechanisms to the initial AGW such as "natural" rain forest/other forest fires, rainforest/other forest death from heat stress, heat loving bacteria breaking down organic matter, increased water vapour (also a very powerful greenhouse) from warming rivers, seas and oceans, methane (also a very powerful greenhouse gas) released by melting permafrost and ice sheets and the Clathate (aka Methane Hydrates) Gun mechanism, just how hot will Earth become?

 

Will Earth become as hot or even hotter than Venus with average global temperatures of 400C through 500C?  Could Earth singlehandedly due to us mere humans become not just the hottest planet in the universe but extremely hot with average global temperatures in the 500C through 1000C range?  Theoretically if virtually the whole troposphere averages much above 100C (the boiling point of water), then such extreme greenhouse heating would be virtually permanent because every molecule of water from the land and oceans will be permanently lofted into the atmosphere as water vapour and remain so since the air will be "too hot" for clouds and rain to form and wash it out.

 

Streuth Craig whether the earth could zoom into a runaway greenhouse scenario purely by adding GHGs is extremely complicated and well beyond my little brain I think it unlikely and I suspect that currently solar luminosity is the key. As the SL continues to increase the Earth will pass the 291 W/m2 threshhold when a runaway becomes possible in about 700 million years. Venus went down the runaway route but it's luminosity was greater. Just a recap on the thinking on Venus taken from Principles of Planetary Climate.

 

Presumably, Venus started out with a composition rather similar to Earth. What went wrong? Why did it keep most of its C02 in its atmosphere, whereas most of Earth's C02 got bound up in carbonate rocks? Where did its water go? The answer came in 1967 with the theory of the runaway greenhouse, formulated first by M. Kombayashi and independently rediscovered shortly thereafter by Andrew Ingersoll of Caltech. This theory puts together two simple bits of physics, the first being that water vapor content of a saturated atmosphere increases exponentially with temperature (Chapter 2), and the second being that water vapor is a greenhouse gas (Chapter 4). When the two are put together, it is found that a planet which receives sufficient solar radiation can get into a runaway cycle where the planet warms in response to absorbed sunlight, which causes more water vapor to enter the atmosphere, which causes more greenhouse effect, which leads to further warming in an unstable feedback loop that doesn't end until the entire ocean is evaporated into the atmosphere. At that point, the water vapor in the upper atmosphere breaks down into hydrogen and oxygen under the influence of high-energy solar radiation, and the hydrogen escapes to space while the oxygen reacts with rocks. Without liquid water, the Urey reaction which turns C02 into limestone cannot take place, so all the outgassed C02 stays in the atmosphere. The runaway greenhouse theory (explored in Chapter 4) gives rather precise predictions of the circumstances under which a runaway can occur, and explains why  Earth did not undergo a runaway despite the fact that it has a water ocean. The work of Kombayashi and Ingersoll is another example of the general idea that big ideas come from simple models. Their reasoning was based on simple radiation models of the sort developed in the first half of Chapter 4. This work also illustrates another general principle of planetary climate: profound results can be obtained by combining a few bits of very basic physics in a novel way.

 

Not much help I'm afraid

Edited by knocker
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Thanks Knocker that was very interesting and informative stuff.  That means that we need to watch out for changes in the amount and rate of chemical weathering to determine the likelihood of any long lasting major runaway greenhouse effect or even just shorter lived and modest runaway warming events.  That also means that going the other way in the period of 55000000 through 3000000 years ago, the development of major mountain chains such as the Tibetan Plateau/Himalayas and the Rockies and Andes with their associated rainfall driven chemical weathering breaking down CO2 in concert with the formation of the current continental and ocean configuration must have been fundamental in the transition from the long trans Permian-Pliocene Greenhouse period to the Quaternary Icehouse period.

Edited by Craig Evans

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Thanks Knocker that was very interesting and informative stuff.  That means that we need to watch out for changes in the amount and rate of chemical weathering to determine the likelihood of any major runaway greenhouse effect.

 

Well that certainly plays a key role but as I mentioned it's a tad complicated. I'll trying reading it all again over the next few days when my brain is in gear to see if I can glean the salients points of which there are many. I might be some time :)

Edited by knocker
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Call me paranoid but the rapid increase in greenhouse gases along with the rapid increase in global temperatures over the last 30 years but even more so over the last 6 years has now got me seriously contemplating, just what would the absolute worst case scenario be from Anthropogenic Global Warming?

 

 

 

As there hasn't been any rapid increase in global temperatures , in need no increase in the last 17 years I wouldn't worry about it unless you are going to live to a grand old age of cira 

 

Four billion years from now, the increase in the Earth's surface temperature will cause a runaway greenhouse effect. By that point, most if not all the life on the surface will be extinct.[12][13] The most probable fate of the planet is absorption by the Sun in about 7.5 billion years, after the star has entered the red giant phase and expanded to cross the planet's current orbit.

 

 

http://en.wikipedia.org/wiki/Future_of_the_Earth

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I may be wrong by it is my understanding that Venus does not have a magnetic field as we do on Earth, probably because it revolved so slowly, and this does not give the same protection against the solar wind as we have - this leads to the lighter molecules being more easily stripped from the planets atmosphere whilst the heaver ones such as CO2 have built up over the vast periods of time and this heavy concentration of the gas led to a runaway greenhouse effect there.

On the other hand Mars does not have a magnetic field either but I believe lost this for different reasons i.e that being that with this planet beng so much smaller than ours the core has solidified and as I understand a liquid core is necessary for the continuance of a magnetic field. Here most of the atmospheric molecules have been stripped aŵay leaving a much thinner atmosphere, again consisting of large amounts of CO2 but too little to have a substantial warming effect.

It is simplistic I know and no doubt there is a lot more involved than this.

As far as our Earth is concerned there is a possibility of runaway heating which would be caused through passing several trigger points, such as the releasing of methane trapped in the tundra and the ocean depths thought warming, the diminishing albedo effect through the melting of the ice, the added water vapour in the atmosphere together with other events which may not be immediately obvious.

At the same time the Earth does have cycles where it alternates between warm and cold - my betting is that the time will come in the next few decades when the sense of urgency will increase to the extent that mankind generally will realise that something really must be done to slow down this warming effect and that we end up with a warming of say 4C by the end of the century and that by the time it reaches 2C of warming by the middle of the century the results will be evident to the extent that our hand will be forced, otherwise we will be in dire straits.

Other than that as time progresses the sun will gradually get hotter and we can do nothing about this, so we have the prospect of life on Earth being extinguished altogether in about 2 billion years time.

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I may be wrong by it is my understanding that Venus does not have a magnetic field as we do on Earth, probably because it revolved so slowly, and this does not give the same protection against the solar wind as we have - this leads to the lighter molecules being more easily stripped from the planets atmosphere whilst the heaver ones such as CO2 have built up over the vast periods of time and this heavy concentration of the gas led to a runaway greenhouse effect there.

On the other hand Mars does not have a magnetic field either but I believe lost this for different reasons i.e that being that with this planet beng so much smaller than ours the core has solidified and as I understand a liquid core is necessary for the continuance of a magnetic field. Here most of the atmospheric molecules have been stripped aŵay leaving a much thinner atmosphere, again consisting of large amounts of CO2 but too little to have a substantial warming effect.

It is simplistic I know and no doubt there is a lot more involved than this.

As far as our Earth is concerned there is a possibility of runaway heating which would be caused through passing several trigger points, such as the releasing of methane trapped in the tundra and the ocean depths thought warming, the diminishing albedo effect through the melting of the ice, the added water vapour in the atmosphere together with other events which may not be immediately obvious.

At the same time the Earth does have cycles where it alternates between warm and cold - my betting is that the time will come in the next few decades when the sense of urgency will increase to the extent that mankind generally will realise that something really must be done to slow down this warming effect and that we end up with a warming of say 4C by the end of the century and that by the time it reaches 2C of warming by the middle of the century the results will be evident to the extent that our hand will be forced, otherwise we will be in dire straits.

Other than that as time progresses the sun will gradually get hotter and we can do nothing about this, so we have the prospect of life on Earth being extinguished altogether in about 2 billion years time.

 

Mike as far as I'm aware the accepted theory regarding Venus is the one I posted above. Or put another way.

 

The runaway greenhouse phenomenon may explain how Venus wound up with such a radically different climate from Earth, despite having started out in a rather similar state. The standard story goes something like this: Venus started with an ocean, and with most of its C02 bound up in rocks as is the case for Earth. However, it was just closer enough to the Sun to trigger a runaway greenhouse. Once the entire ocean had evaporated into the atmosphere, there was so much water vapor in the upper atmosphere that it could be broken apart by energetic solar ultraviolet rays, whereafter the light hydrogen could escape to space. The highly reactive oxygen left behind would react to form minerals at the surface. Once there was no more liquid water in play, the reactions that bind up carbon dioxide in rocks could no longer take place, so all the planet's C02 outgassed from volcanism and stayed in the atmosphere, leading to the hot, dry super-dense atmosphere of modern Venus.

Edited by knocker
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Past climates - A little snippet about the PETM

 

Figure 1.9 exhibits a dramatic climate event of considerable importance. The spike in 18O at the Paleocene/Eocene boundary (marked "PETM" in the figure, for Paleocene/l Eocene Thermal Maximum) is not a glitch in the data. It represents a real, abrupt and massive transient warm event. The spike looks small in comparison to the range of isotopic variation over the past 70 million years, but in fact it represents the planet accomplishing two million years' worth of warming in a warm spike that (on closer examination) sets in within 10 000 years and has a duration of around 200 000 years. This isotopic excursion corresponds to a global warming of about 4C; other proxy records show that the warming had similar magnitude in the Arctic and at the Equator, and that it extended to the deep ocean. This climate event triggered a mass extinction of benthic species, probably due to a combination of warming, oxygen depletion, and ocean acidification. An important clue as to the cause of the warming is that the record of 13C from the same core (not shown) exhibits a major negative excursion at the same time, going from values of about + l.2%o down to about zero at the bottom of the excursion. This indicates a catastrophic release of large quantities of isotopically light carbon into the climate system, which presumably increased the atmospheric greenhouse effect and led to warming. One possibility is that the release came in the form of methane from destabilized clathrate ices in the ocean sediments; another is that the isotopically light carbon came from oxidation of suddenly exposed organic carbon pools on land, releasing large quantities of C02 . Based on analysis of the carbon isotope record, it has been estimated that 4000-6000 gigatonnes of carbon were released into the ocean-atmosphere system, if the release were from organic matter. This compares with 700 gigatonnes of carbon in the form of C02 in the modern atmosphere. This would considerably enhance the atmospheric greenhouse effect, though the effect would largely wear off after a thousand years or so, over which time about 80% of the released carbon would have worked its way into the ocean. It is far from clear that one can account for the observed magnitude and duration of PETM warming with the amount of carbon one has at one's disposal. This is one of the Big Questions.

 

Source: Principles of Planetary Climate, Raymond T. Pierrehumbert

Edited by knocker
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Mike as far as I'm aware the accepted theory regarding Venus is the one I posted above. Or put another way.

 

The runaway greenhouse phenomenon may explain how Venus wound up with such a radically different climate from Earth, despite having started out in a rather similar state. The standard story goes something like this: Venus started with an ocean, and with most of its C02 bound up in rocks as is the case for Earth. However, it was just closer enough to the Sun to trigger a runaway greenhouse. Once the entire ocean had evaporated into the atmosphere, there was so much water vapor in the upper atmosphere that it could be broken apart by energetic solar ultraviolet rays, whereafter the light hydrogen could escape to space. The highly reactive oxygen left behind would react to form minerals at the surface. Once there was no more liquid water in play, the reactions that bind up carbon dioxide in rocks could no longer take place, so all the planet's C02 outgassed from volcanism and stayed in the atmosphere, leading to the hot, dry super-dense atmosphere of modern Venus.

I am not disputing what you say Knocker but saying that the virtual absence of a magnetic field probably speeded things up a little without the protection of the magnetosphere protecting the planet from the worst effects of solar radiation allowing free hydrogen to be dissipated more easily into space.

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I may be wrong by it is my understanding that Venus does not have a magnetic field as we do on Earth, probably because it revolved so slowly, and this does not give the same protection against the solar wind as we have - this leads to the lighter molecules being more easily stripped from the planets atmosphere whilst the heaver ones such as CO2 have built up over the vast periods of time and this heavy concentration of the gas led to a runaway greenhouse effect there.

On the other hand Mars does not have a magnetic field either but I believe lost this for different reasons i.e that being that with this planet beng so much smaller than ours the core has solidified and as I understand a liquid core is necessary for the continuance of a magnetic field. Here most of the atmospheric molecules have been stripped aŵay leaving a much thinner atmosphere, again consisting of large amounts of CO2 but too little to have a substantial warming effect.

It is simplistic I know and no doubt there is a lot more involved than this.

As far as our Earth is concerned there is a possibility of runaway heating which would be caused through passing several trigger points, such as the releasing of methane trapped in the tundra and the ocean depths thought warming, the diminishing albedo effect through the melting of the ice, the added water vapour in the atmosphere together with other events which may not be immediately obvious.

At the same time the Earth does have cycles where it alternates between warm and cold - my betting is that the time will come in the next few decades when the sense of urgency will increase to the extent that mankind generally will realise that something really must be done to slow down this warming effect and that we end up with a warming of say 4C by the end of the century and that by the time it reaches 2C of warming by the middle of the century the results will be evident to the extent that our hand will be forced, otherwise we will be in dire straits.

Other than that as time progresses the sun will gradually get hotter and we can do nothing about this, so we have the prospect of life on Earth being extinguished altogether in about 2 billion years time.

 

@ Mike Meehan

 

Oh, I dunno:  Maybe by then mankind will have developed the technology to fire massive 1 million ton cannons from the daytime side of the Earth towards the Sun so that the Recoil Force will push the Earth outwards into an orbit further away from the Sun.  Alternatively a massively big (and long) chain could be attached from the Earth away from the Sun with a very powerful engine at the other end to pull the Earth away from the Sun; this engine would be powered by tons of water through nuclear fusion.  But that is indeed a very long way off and millions of generations will need to pass for the very long-term (multi-million year means) Solar output to rise by just 3%; as a Christian I believe God will scrumple up the known Universe and He will give us a new Heaven and a new Earth long before then!!

 

A much bigger possibility sometime in the next 500 years is not a warming one but a severe cataclysmic cooling caused either by all-out nuclear war causing a "Nuclear Winter", or the big supervolcano of Yellowstone National Park in the US blowing its top putting so much ash and sulphur into the stratosphere that the World cools by over 10C for several years:  When that happens snow and ice will increase to such a massive, massive extent that the Earth`s albedo increases some 15% and the intense cold will thus entrench permanently leading to the commencement of the next Ice Age proper.  How will we in Britain cope with winter temperatures of -50C across the South with glaciers building up over all land north of Birmingham (not to mention the effects of radiation fall-out if the cooling had originally been caused by nuclear war)??

 

Ian

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