Climate scientists have identified a number of positive feedback mechanisms which are considered likely cause global warming to accelerate, if temperatures continue to rise unabated. Some of these feedback effects are expected to increase steadily as temperatures increase, whereas others may start to kick in after temperatures rise above a certain threshold.
But these feedback mechanisms are not generally included in climate models, because they're difficult to quantify; it's not yet clear exactly where the relevant 'tipping points' are, or how quickly each mechanism they would then come into effect.
Of course, that certainly doesn't mean they WON'T happen. It just means that all the major climate models referenced by IPCC, and described by the denialists as "alarmist" propaganda, are in fact conservative. The worst-case-scenarios, with postive feedback accelerating global warming, aren't even included in the models.
On skeptical websites and blogs, the idea runaway global warming, if mentioned at all, is ridiculed and dismissed as "chicken-littlism". But these sites seem remarkably silent about the feedback mechanisms themselves... and what might be wrong with them.
Presumably, since they argue that even the conservative IPCC climate predictions are wild, alarmist exaggeration, skeptics must very have good scientific reasons for thinking that none of these positive feedback mechanisms will actually occur.
I'd like to know exactly what these scientific reasons are -- if they exist at all. Here are some of the positive feedback mechanisms that have been studied, so far.
1. WARMING OCEANS ABSORB LESS CO2 >> CO2 LEVELS RISE FASTER .. MORE WARMING
Warming oceans are more thermally stable. This stability reduces the circulation of nutrients and decreases the biomass of the photoplankton in the ocean -- which play a crucial role in the carbon cycle, removing CO2 from the atmosphere and deposting it on the sea bed. As a result, amospheric CO2 will rise faster, causing more warming.
2. SLOWER HEALING OF OZONE LAYER >> UV KILLS PHYTOPLANKTON.. MORE WARMING
Climate models predict that as the troposphere (the lower part of the atmosphere) warms due to CO2, the outer stratosphere will cool. This is because more of the heat that is reflected from the earth is trapped by greenhouse gases in the troposphere -- and therefore, doesn't get to the stratosphere to warm it up. Replenishment of ozone in the stratosphere is slower at cooler temperatures, so this cooling effect will hold back the slow, gradual healing of the ozone layer. Until it heals completely, harmful UV radiation gets through -- especially in the southern oceans around the antarctic. This reduces the biomass of phytoplankton still further. Less CO2 is taken out of the atmosphere, so global warming is accelerated.
As temperatures rise, artic sea ice will continue to thin and retreat. This thinning reduces the albedo (the net reflectivity of the planet), thus leading to further warming.
4. LONGER TROPICAL DRY SEASON >> FOREST FIRES >> MORE CO2... MORE WARMING
Tropical rain forests are one of the world's biggest "carbon sinks", containing at least as much CO2 as ALL the emissions ever produced by human activity. Rainforest ecologists know that in the past, natural climate changes have caused huge areas of forest to rapidly disappear, to be replaced by savannah. All it takes is an extended dry season, due to rising global temperatures -- making the forests highly vulnerable to wildfires. When they burn, the rainforests will release massive amounts of C02 into the atmosphere, causing further warming.
5. MELTING OF PERMAFROST >> METHANE RELEASED >>... MORE WARMING
Beneath the permafrost in Alaska, Canada, Greenland and Siberia there is buried a vast carbon sink, in the form of methane (from rotted vegetation). As a greenhouse gas, methane is over 20 times more potent than CO2. When the permafrost melts, methane seeps out of the soil underneath. Recent studies in Siberia have found huge areas of tundra in which the permafrost is melting -- and this will continue as temperatures rise. On a conservative assumption that the release of buried methane will be gradual and slow, it's estimated that this would be sufficient to raise temperatures by at least 5 degrees over the next 50 years (thats in addition to the warming due to increased C02).
5. WARMING OCEANS RELEASE METHANE FROM SEABED >>... MORE WARMING
Another huge methane carbon sink is buried at the bottom of the oceans, in the form of deposits called "methyl hydates" or "methyl clathrates". When the temperature of the ocean rises, these icy deposits melt -- and the trapped methane bubbles to the surface. Fortunately, at the moment, this is a rare and localised occurence. The average temperature of the oceans isn't high enough -- YET -- for this process to occur on a large. But as global temperatures rise and the oceans warm, it becomes increasingly likely that this will happen.
6. THE DOMINO EFFECT: FEEDBACK MECHANISMS TRIGGER EACH OTHER >> MASSIVE WARMING
Of course, if temperatures rise sufficiently to make just ONE of the above feedback mechanism kick in and accelerate the warming trend, this greatly increases the likelihood that other feedback effects will be triggered too -- and within a shorter time frame. If this domino happens, with each feedback mechanism triggering others, the standard IPCC scenario of temperatures gradually rising over the next century (which the skeptics call "alarmist propaganda" may prove hopelessly optimistic. Instead, the climate could rapidly "flip" into a much warmer phase, perhaps 10-15 degrees warmer than it is today.
A CHALLENGE TO SCENTIFICALLY-MINDED SKEPTICS
There are some "moderate" skeptics, like Bjorn Lomborg, who accept that C02 emissions are an important factor in global warming... and that substantially curbing these emissions would indeed mitigate the warming trend. However, they argue that the economic cost of such a policy too great. The best strategy, they say, is just to ACCEPT that temperatures are gradually warming and devote our resources to ADAPTING to ongoing climate change.
On the other hand, the Stern Report argues that the harmful economic impact of the IPCC's conservatively forecast, gradual temperature rises over the next few decades would be very much greater than the cost of taking the proposed measures now. Skeptics disagree with this -- and claim that Stern has got his sums wrong.
However, I don't wish to argue about the Stern report right now. This debate aside, one thing, surely, remains perfectly clear.
If there really IS a serious risk that the present warming trend will trigger drastically accelerated warming, via positive feedback, then the "do nothing, wait and see, cross your fingers and hope for the best" stragegy is reckless in the extreme.
I'm not suggesting here for a moment that skeptics ARE that insane -- On the contrary, I'm assuming that skeptics must be pretty sure that accelerated warming is highly UNLIKELY.
I'd just like to know why.
I would like to see some carefully argued, rational, scientific arguments which explain why EVERY ONE of these feedback mechanisms is EXTREMELY UNLIKELY to occur and cause a serious acceleration of global warming.
If you can't manage that, then it'll be clear to everyone that the accelerated warming scenario is at the very least, a significant possibility -- perhap even a strong likelihood. In that case, we'd obviously be crazy not to take such a risk seriously -- and do everything in our power to prevent such a catastrophe from happening.
In other words, unless skeptics can provide the arguments I've asked for, their position on climate policy really is insane.
No one in their right mind would argue that:
(a) yes, we can't refute the arguments which say that postive feedback mechanisms are likely to occur within the next few decades, if nothing is done to mitigate CO2 emissions... We certainly can't prove that, on the contrary, the risk of accelerated warming is very low.
(b) never mind; let's just ASSUME that the risk is low anyway. Let's HOPE that runaway global warming doesn't happen. Let's play an optimistic game of Russian roulette with the planet -- and continue burning fossil fuels like there's no tomorrow. Surely, the benefits of cheap flights and fast cars are worth the risk?
OVER TO YOU, SKEPTICS!
* Free-thinking does not just mean choosing to believe whatever makes you feel good. There's no thought at all in that. *
Hey, I got news for you. Climate always change. It's a natural thing to happen and has been happening for a very long time indeed without any help from humans. So unless you tell me it matters that we control man made CO2, this post is pointless. So let's assume that you are omnipotent and can control man made CO2 at whatever level you want, can you then claim you can MAKE the climate? and can this claim be backed by any peer reviewed science?
which shows the relationship for Ozone is somewhat more complex than blaming warming in addition to CFC's.
3. Sea ice is at it's greatest in winter when it's dark all day round at the poles so what use is the white albedo then?. It retreats in the summer when it's light, always has done since the ice age. The white area in the summer receives only glancing light from the sun because of the latitude so only ever likely to be a minor feedback.
4. Global Average Temperature has not risen since 1998.
5. the range of IPCC reported warming over the next 100 years is between 1.5 deg C and 11. deg C. You indicate that we will get a 5 deg C contribution from Tundra over 50 years. Have IPCC ignored this or excluding Tundra are they predicting a temperature increase between - 3.5 deC and 8 deg C?
Your 2nd 5. See 1. Oceans are cooling.
6. If 6 happens then governments will implement seeding of the atmosphere with some form of reflective particles, but given 1-5 when will we get to 6?
Some interesting points here, for me to get my teeth into.
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Originally posted by Son of Mulder: 1. Oceans are currently cooling.
Thanks for the link to this paper, it's very interesting. If you read it through, you'll notice that it doesn't suggest that there is an ongoing cooling trend... and it certainly doesn't predict that cooling will continue. It describes a short-term, two-year "cooling event", i.e., a dip in an otherwise upward warming trend, which the author compares with a similar event between 1980 and 1983... after which temperatures continued to rise, as they have since 1955.
As the introduction states: "These increases provide strong evidence of global warming. Climate models exhibit similar rates of ocean warming, but only when forced by anthropogenic influences."
This is a common fallacy. It's true that according to NASA's global temperature estimates (which are the basis of NOAA reports), 1998 was the hottest year on record. However, that's not surprising: there was an El Nino in 1998 which tends to raise temperatures a little anyway.
In any case, if you take the *average* of global temperatures between 1998 and 2006 -- and compare that with the average of the eight years up to and including 1998, you'll find that the past 8-year average is higher than the previous 8 years... which means that temperatures are still rising.
Incidentally, while the Met Office's Hadley Center's temp record agrees very closely with the Nasa data, there are some discrepancies. According to Hadley, 2005 was warmer that 1998 - and of course, there was no El Nino in 2005. It's considered quite likely that 2007 will be another record year, since we're apparently due for another El Nino.
Bottom line: global temperatures are still rising.
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2. Ozone hole has been mending since CFC's removed from market.
which shows the relationship for Ozone is somewhat more complex than blaming warming in addition to CFC's.
No, it hasn't mended, -- as the Science Daily article reports, it's *started* to heal, which is great; however, the process is slow; 20 years after the Montreal protocol and still in 2005 there was the biggest antarctic hole ever!
Anyway, I'm not blaming warming on increasing CFCs -- they're not increasing... and their direct effect on global warming is insignificant. The mechanism we're talking about here is indirect. The point is that increased warming will slow down the healing process; in the meantime, UV radiation coming through the Antarctic hole is killing off lots of phytoplankton... which would otherwise be doing the very useful job of absorbing CO2 out of the atmosphere.
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3. Sea ice is at it's greatest in winter when it's dark all day round at the poles so what use is the white albedo then?. It retreats in the summer when it's light, always has done since the ice age. The white area in the summer receives only glancing light from the sun because of the latitude so only ever likely to be a minor feedback.
OK, this is an interesting and intelligent argument, I'll have to look into it. It puzzles me, because according to the current theory of the mechanism which causes the shift between ice age and warm interglacial, the reduction of ice cap albedo is an important factor. This was realised when it was figured out that the Milankovich mechanism (which gets the temperatures rising to start with) only accounts for about 10% of the total warming trend -- so there have to be feedback mechanisms. The obvious one is CO2, being released from warmer oceans (with the much debated 800-year time lag). But I understand that this CO2 forcing isn't enough to account for all of the remaining 90%... and it's thought that decreasing ice albedo makes a major contribution.
Good argument though...
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4. Global Average Temperature has not risen since 1998.
See above.
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5. the range of IPCC reported warming over the next 100 years is between 1.5 deg C and 11. deg C. You indicate that we will get a 5 deg C contribution from Tundra over 50 years. Have IPCC ignored this or excluding Tundra are they predicting a temperature increase between - 3.5 deC and 8 deg C?
I think you'll find the latests IPCC forecasts for end of century temperatures compared to 2000 figures is between a "low scenario" of +1.8°C and a "higher scenario" of +4.0°C. These are expected decadal averages; the likely range of temperatures at the higher scenario is estimated at +2.4 to _6.4°C, i.e., +4.3 to +11.5° FAHRENHEIT. (I understand the latter figure has been inadvertently misquoted by some journalists as centigrade).
To answer your question, these forecasts in the "summary for policy makers" don't estimates of additional warming due to methane emissions from melting permafrost. There will be discussion of this mechanism in the full report, which is due out soon.
In the meantime, let's assume for the sake of argument that the permafrosts WILL melt and that the methane emitted will contribute about +5°C to global temperatures. Adding this to the IPCC forecasts, we get a decadal average in 2100 of between +6.8°C and +9.0°C.
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Your 2nd 5. See 1. Oceans are cooling.
See above.
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6. If 6 happens then governments will implement seeding of the atmosphere with some form of reflective particles, but given 1-5 when will we get to 6?
If six happens, there may not be enough time to develop these technologies. I think emission reduction strategies are our best bet for at least slowing down the warming trend -- and buying ourselves some time to come up with solutions like this.
Anyway, given that global temperatures are still, in fact, rising -- and that ocean temperatures are fully espected to rise with them, not withstanding the occasional 2-3 year temperature "dips" -- we may well get to 1-5 sooner than you think.
* Free-thinking does not just mean choosing to believe whatever makes you feel good. There's no thought at all in that. *
Roger58, I started this thread to have a dialog about scientific matters with reasonable, open-minded skeptics -- like Son of Mulder. He understood the point of my original posting... but you just wade in with grossly offensive insults and abuse.
For the record: no, I DON'T look forward to environmental catastrophe. I have a family - and I don't want to see the next generation growing up in an ever more unstable, dangerous world.
I actually quite like of this planet -- and with few highly annoying individual exceptions, I'm quite fond of humanity too. I'd therefore kinda prefer it if we don't render the place unfit for human habitation.
No, I'm not against development, I'm 100 per cent for it -- and I don't want everything to go "backwards." I'm just in favour of smart, resource-efficient, development -- not the stupid kind.
* Free-thinking does not just mean choosing to believe whatever makes you feel good. There's no thought at all in that. *
If you read it through, you'll notice that it doesn't suggest that there is an ongoing cooling trend... and it certainly doesn't predict that cooling will continue. It describes a short-term, two-year "cooling event",
This is about actual measurement any further statment about blip etc is speculation. We'll have to wait and see.
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In any case, if you take the *average* of global temperatures between 1998 and 2006 -- and compare that with the average of the eight years up to and including 1998, you'll find that the past 8-year average is higher than the previous 8 years... which means that temperatures are still rising.
No I'm afraid the record shows temperatures were rising and now they've tended to flatten. So you'd expect an earlier 8 year average to be lower than the most recent 8 years
2.
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Anyway, I'm not blaming warming on increasing CFCs -- they're not increasing... and their direct effect on global warming is insignificant. The mechanism we're talking about here is indirect
In your original posting you were suggesting that warming was slowing the replenishment of Ozone because it caused Troposphere cooling. My point was that many other factors affect Ozone as indicated in the article. So I'm not sure how reasonable your assertion is in today's circumstances.
3.
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It puzzles me, because according to the current theory of the mechanism which causes the shift between ice age and warm interglacial, the reduction of ice cap albedo is an important factor
Puzzles me as well additionally if it's much whiter then it's going to radiate less heat (Boltzmann). So there's a warming effect of white albedo in the dark I'd have thopught.
4. See 1.
5. Looks like we wait for IPCC on this one but I'd be particularly to hear what the assessed probability of tundra melting is.
6.
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If six happens, there may not be enough time to develop these technologies
Given the levels of uncertainty about how great or small the threat of runaway warming is I'd bet your bottom dollar that governments are seriously developing such a contingency plan.
No I'm afraid the record shows temperatures were rising and now they've tended to flatten. So you'd expect an earlier 8 year average to be lower than the most recent 8 years
Whoops, I inadvertently typed the above in the quote box. It was my reply to the average temperature debate.
Originally posted by TheHeretic: Roger58, I started this thread to have a dialog about scientific matters with reasonable, open-minded skeptics -- like Son of Mulder. He understood the point of my original posting... but you just wade in with grossly offensive insults and abuse.
For the record: no, I DON'T look forward to environmental catastrophe. I have a family - and I don't want to see the next generation growing up in an ever more unstable, dangerous world.
I actually quite like of this planet -- and with few highly annoying individual exceptions, I'm quite fond of humanity too. I'd therefore kinda prefer it if we don't render the place unfit for human habitation.
No, I'm not against development, I'm 100 per cent for it -- and I don't want everything to go "backwards." I'm just in favour of smart, resource-efficient, development -- not the stupid kind.
Well Herry (you don't mind if I call you Herry do you?), you started this thread because something puzzled you and you wanted some people to help you find an answer.
If you look up the word 'sceptic' in the OED, you'll see its definition is 'a person inclined to question or doubt accepted opinion'. So, when you think about it, it follows that there is no such thing as the 'close-minded sceptic' the first sentence of your reply alludes to.
So, now that we know this, your initial question can be re-phrased as: Can open-minded people - who are inclined to question accepted opinion - help me find out why the world isn't going to end?
Next, you say you "started this thread to have a dialog about scientific matters" and yet when I use a broad range of scientific enquiry to help you with the important question you are stuck to find an answer to, you claim the science is grossly offensive, insulting and abusive to you.
Needless to say, it will be difficult for you to find an answer (and for me to help you - as you asked me to) whilst you hold on to this view of science. As an illustration, your question would then need to be phrased as: Can grossly offensive, insulting and abusive people help me find out why the world isn't going to end without being grossly offensive, insulting and abusive?
or, meaning exactly the same for you: Can scientifically-minded people help me find out why the world isn't going to end without being scientifically-minded?
Clearly your question is going to remain unanswered here. That is: SOMETHING (other than the world) has got to end before you can begin moving forward with the enquiry you are stuck with.
Its useful to ask yourself at this point if you REALLY do want your question answered at all?
From your reply, it's obvious to see that your experience of the current world you live in is one that's "ever more unstable, dangerous" and potentially catastrophic for you - on top of containing people you find grossly offensive, insulting and abusive. So, it would be fair to say, you don't currently feel your world is much of a place you enjoy being in. And carrying this view around makes it understandable to me why you harbour a wish that your current world will end.
So, your fully-formed question would be better understood and answered if you presented it as: Can open-minded people help me find out why my unstable, dangerous, catastrophic, grossly offensive, insulting and abusive world isn't going to end - as I wish it would - so that I can replace it with the world I want to be in and then get on with life with my family instead of spending so much time on the internet?
When you are able to reach this point of honesty we can all recognise it as a 'development' and work together to begin finding a real answer to your question. But if you keep insisting on excluding your own human nature out of your enquiry all about nature itself (by claiming open-minded people are being 'personal' when they invite your nature to be included), then you'll remain stuck.
I wish half as much effort had been put into finding negative feedback mechanisms as in finding positive ones.
I think there is at least one major one, plus a limiter:
FASTER PLANT GROWTH - NEGATIVE FEEDBACK
Increased temperatures (particularly if coupled with increased precipitation) ought to increase plant and tree growth, thereby providing a larger carbon sink. I believe this is happening in the Amazon.
CO2 HAS LIMITED HEAT ABSORBING ABILITY - LIMITER
As the concentration of CO2 in the atmosphere increases, the marginal ability to absorb heat decreases rapidly. Therefore more of the "excess heat" should escape into the upper atmosphere and away.
In addition, there is another giant unknown, which might well act as a negative feedback:
INCREASED CLOUD COVER - POSSIBLE NEGATIVE FEEDBACK
This could cut either way, but if the increased cloud cover that higher CO2 possibly causes stops the sun's heat from reaching the surface, then this will be a negative feedback. However, it will also serve to trap more heat under the cloud level.
All of which speaks to me of the need to spend some research funding on studying and modelling these potential negative feedbacks.
Originally posted by Son of Mulder: [Re. 3-year drop in ocean surface temperatures] This is about actual measurement any further statment about blip etc is speculation. We'll have to wait and see.
It's more than just speculation. As the article mentions, ocean surface temperatures have been rising at least since at 1955. That's exactly what you'd expect, given rising global temperatures, due to rising greenhouse gas emissions. Of course, just like the global temperature record, the graph isn't a straight line -- sometimes there are dips. However, if global temperatures continue to rise, ocean temperatures will also rise; that's inevitable.
So the suggestion that the recent dip is actually the start of a long term cooling phase is speculation... and fairly wild speculation at that, given that there is no theoretic reason to suggest that this is likely.
Way back in the 80s and 90s, skeptics used to point out that "two or three warm years doesn't prove global warming." Absolutely correct; but of course, there have been an awful lot of record-breaking years lately. And the point cuts both ways. In a period in which ocean temperatures have steadily risen for decades -- just as we'd expect, given rising GHGs -- one or two years of slight cooling doesn't tell us that the warming trend has stopped. It didn't stop in the 1980s, when temperatures dipped and then continued to rise. And with GHGs still rising, there's no good reason to expect that they won't continue to rise for decades to come.
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[Re. Temperatures flattening since 1998] No I'm afraid the record shows temperatures were rising and now they've tended to flatten. So you'd expect an earlier 8 year average to be lower than the most recent 8 years
This "temperatures flattening since 1998" claim crops up a lot on skeptical websites -- but I've not been able to find any peer-reviewed papers which say this. Can you give me a reference?
By the way, it seems I was incorrect in saying that NASA identify 1998 as the hottest year on record. It seems they did, until they analysed their data from 2005... and found it was hotter, in spite of the fact that temperatures weren't boosted by an El Nino.
So there doesn't seem to be any good evidence to suggest that temperatures have "flattened" since 1998. Once again, may I remind you of the long-forgotten skeptical argument: "a few unusually warm years doesn't confirm global warming". Absolutely correct -- however:
every year since 1917 has been warmer than 1917 every year since 1956 has been warmer than 1956 every year since 1992 has been warmer than 1992 every year since 1976 has been warmer than 1976 the ten hottest years on record occured in the last 15 the 20 hottest years on record occured in the last 25
That seems like pretty good evidence to me. In this context, after the exceptionally warm year of 1998 -- boosted 0.2°C above the trend line by that years' El Nino -- a few very slightly cooler years DOES NOT TELL US THAT TEMPERATURES ARE FLATTENING... particularly, since this period includes the still hotter year of 2005 (WITHOUT the added effect of an El Nino), and four more of the six hottest years on record.
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[Re. slowed healing of ozone layer and UV harm to phytoplankton] In your original posting you were suggesting that warming was slowing the replenishment of Ozone because it caused Troposphere cooling. My point was that many other factors affect Ozone as indicated in the article. So I'm not sure how reasonable your assertion is in today's circumstances.
I'm inclined to agree. Once again, you've prompted me to look up some very interesting papers, which come differing conclusions. The Science daily article you linked to refers to two recent papers:
1. http://www.sgo.fi/Events/ltt-2006/LTT2006_abstracts/Wea...ndersen_abstract.pdf The abstract states that: "Although recent data suggest that total column ozone abundances have at least not decreased over the past eight years for most of the world, it is still uncertain whether this improvement is actually attributable to the observed decline in the amount of ozone-depleting substances in the Earth\'s atmosphere. The high natural variability in ozone abundances, due in part to the solar cycle as well as changes in transport and temperature, could override the relatively small changes expected from the recent decrease in ozone-depleting substances. Whatever the benefits of the Montreal agreement, recovery of ozone is likely to occur in a different atmospheric environment, with changes expected in atmospheric transport, temperature and important trace gases. It is therefore unlikely that ozone will stabilize at levels observed before 1980, when a decline in ozone concentrations was first observed."
On the other hand: the other paper cited is far more optimistic. 2. http://ciencia.nasa.gov/headlines/y2006/images/ozone/preprint.pdf The abstract states that: "Multiple satellite and ground-based observations provide consistent evidence that the thickness of Earth’s protective ozone layer has stopped declining since 1997.... [this and other studies are] consistent with a leveling off of stratospheric abundances of chlorine and bromine, due to the Montreal Protocol and its amendments... [However] Even with this evidence that the Montreal Protocol and its amendments are having the desired, positive effect on ozone above 18 km, total column ozone is recovering faster than expected due to the apparent transport driven changes at lower altitudes. Accurate prediction of future levels of stratospheric ozone will require comprehensive understanding of the factors that drive temporal changes at various altitudes, and partitioning of the recent transport-driven increases between natural variability and changes in atmospheric structure perhaps related to anthropogenic climate change."
So, I think we can agree that the jury is out on the rate of recovery of the ozone layer and the effects this may have on possible UV-related feedback mechanisms.
[Re. ice-albedo feedback] Puzzles me as well additionally if it's much whiter then it's going to radiate less heat (Boltzmann). So there's a warming effect of white albedo in the dark I'd have thought. [from your previous posting]Sea ice is at it's greatest in winter when it's dark all day round at the poles so what use is the white albedo then?. It retreats in the summer when it's light, always has done since the ice age. The white area in the summer receives only glancing light from the sun because of the latitude so only ever likely to be a minor feedback.
The albedo effect isn't about radiating heat, its about reflecting light -- so this point is irrelevant. Besides, ice caps are very, very COLD... they don't have a lot of heat to radiate! Their failure to radiate heat certainly isn't going to make the planet *warmer*... If it did, how do you suppose the much larger ice-caps during the ice ages managed to persist for 100s of 000s of years? This objection is a non-starter.
Having throught through your original objections to ice-albedo feedback, it doesn't stands up either. You're right that you can't have an albedo effect without sunshine, so we're talking about the summertime ice-cover... And sure, ice always retreats during the summer. The point is, it is now retreating a great deal MORE, which means that the albedo effect is reduced. Sure, as you point out, the sun is at a lower angle in the sky than it is the tropics -- however, this is offset by the fact that during the summer, the poles get 24 hours of sunlight, rather than 12. So summer ice cover is extremely relevant to the Arctic heat budget.
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[Re. melting permafrosts] Looks like we wait for IPCC on this one but I'd be particularly to hear what the assessed probability of tundra melting is.
I understand there will be data on that in the IPCC report, based on work on melting permafrost in Siberia. Direct studies of the temperatures at which the permafrosts melt and (most crucially) release methane -- and also, the rate at which methane is emitted -- should give us a clearer indication of the scale of the problem and the risk it represents.
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[Re. government contingency plans] Given the levels of uncertainty about how great or small the threat of runaway warming is I'd bet your bottom dollar that governments are seriously developing such a contingency plan.
I hope you're right... but I'd rather hang on to my bottom dollars in case the planet really does go belly up -- and my best chances of survival depend on moving somewhere close to Antartica.
I don't have much faith in Governments' ability to plan in the long-term. They've been dragging their feet on the relatively EASY option of curbing GHG emissions. Planet saving technologies like global sun-reflectors in space would likely cost trillions of dollars, and take decades to develop. The risk is that "uncertainty" will remain an excuse for doing nothing, until its too late.
* Free-thinking does not just mean choosing to believe whatever makes you feel good. There's no thought at all in that. *
Originally posted by TheHeretic: every year since 1917 has been warmer than 1917 every year since 1956 has been warmer than 1956 every year since 1992 has been warmer than 1992 every year since 1976 has been warmer than 1976 the ten hottest years on record occured in the last 15 the 20 hottest years on record occured in the last 25
The difficulty with this is the ON RECORD bit. Records in this context do not go back very far.
There is evidence (of sorts) that the world has been warmer at some points in the last two thousand years - just check out where the Romans grew wine.
[Re. melting permafrosts] Looks like we wait for IPCC on this one but I'd be particularly to hear what the assessed probability of tundra melting is.
I understand there will be data on that in the IPCC report, based on work on melting permafrost in Siberia. Direct studies of the temperatures at which the permafrosts melt and (most crucially) release methane -- and also, the rate at which methane is emitted -- should give us a clearer indication of the scale of the problem and the risk it represents.
Do you know whether they mention anything about evidence of former forests being uncovered by melting permafrost? This would suggest that temperatures at some point were taher higher than they are now.
Originally posted by JL(SFC58,AFCB): FASTER PLANT GROWTH - NEGATIVE FEEDBACK Increased temperatures (particularly if coupled with increased precipitation) ought to increase plant and tree growth, thereby providing a larger carbon sink. I believe this is happening in the Amazon.[QUOTE] You'd think so... unfortunately, it doesn't seem to work that way. It turns out that CO2 uptake varies with temperature; the warmer it gets, the less trees respire. Studies have found that in rain forests, trees grow less in warmer years than cooler ones.
In any case, even if rising CO2 did cause substantially greater tree growth, this would only slow down global warming a little... and it wouldnt be much use if the rain forests go up in smoke, because of longer dry seasons making them vulnerable to forest fires. This is exactly how huge areas of forest have turned to savannah in the past -- if it happens in the Amazon, its estimated that more CO2 would be released into the atmosphere than ALL the human emissions since the start of the industrial revolution.
[QUOTE]CO2 HAS LIMITED HEAT ABSORBING ABILITY - LIMITER As the concentration of CO2 in the atmosphere increases, the marginal ability to absorb heat decreases rapidly. Therefore more of the "excess heat" should escape into the upper atmosphere and away.
This is sometimes claimed on skeptical websites, but there's no credible scientific basis for it. You certainly won't find any peer-reviewed scientific papers that support this assertion.
If it were true, Venus should be a great deal cooler. Venus has highest planetary surface temperature in the solar system at around 500°C. Being much further away from the sun, Venus only receives about 25% of the solar energy that warms Mercury -- but Venus is still much hotter, because of to the CO2 greenhouse effect.
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INCREASED CLOUD COVER - POSSIBLE NEGATIVE FEEDBACK This could cut either way, but if the increased cloud cover that higher CO2 possibly causes stops the sun's heat from reaching the surface, then this will be a negative feedback. However, it will also serve to trap more heat under the cloud level.
True, it could cut either way... water vapour is a much more potent greenhouse gas than CO2. It partly depends where increasing cloud cover forms; higher up, the warming effect would predominate, where as lower down, you'd get increased reflection.
At present, all we can say is, there MAY be a net negative feedback effect from increased cloud cover but at the moment, we just don't know. We certainly can't sit back and assume that this effect will be sufficient to stabilize temperatures, in spite of rising CO2 levels, plus the various positive feedback mechanisms I've mentioned.
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All of which speaks to me of the need to spend some research funding on studying and modelling these potential negative feedbacks.
Both positive and negative feedback effects are one of the biggest target areas for research funding right now. A lot of work is being done on clouds, especially.
* Free-thinking does not just mean choosing to believe whatever makes you feel good. There's no thought at all in that. *
When I read that the oceans have cooled for 3 years so far this decade and the global average temperature with respect looks pretty flat to me since 1998 I wondered what the connection might be.
For Global average temp ie 1999/2000 look low 2001/2/3 look slightly rising 2004 looks lower and 2005 looks like 1998 so looks like the graph gradient has flattened over the last 8 years vs 1990-1998.
Also 2003-2005 (what happened in 2006?) for the oceans show cooling. May I hypothesise that the heat from the oceans caused the 2005 rise in global average atmospheric temps vs 2001-2004. If not where did the lost ocean heat go? I'd suggest this means the lack of an El Nino is not directly relevant to the 2005 high.
Concerning albedo
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Besides, ice caps are very, very COLD...they don't have a lot of heat to radiate!
But it is relevant when it comes to Infrared radiation from the earth. If we assume average -37 deg C (figure I found for Antarctica) for all polar regions under ice that is still 236 deg K and if we assume average 20deg C for rest of the planet ie 293 deg K,the Boltzman ratio for identical emmissive surfaces would be (236/293)^4 which is about 0.42 so I'd say there is still a significant radiation component from the poles. Now in an area where the ice melts I'd suggest a higher effective ratio ie a relative cooling tendency. If the ice disappears then the polar emissivity will rise towards the rest of the planet so there would be a cooling effect.
Assume rise to 0 deg C ie 273 deg K (273/293)^4 = .75. Therefore an increase in infrared radiation of (.75/.42) = 79% increase for melted polar areas. This must be significant in the overall energy balance of the planet where the whole debate is about an overall positive average forcing of 1 watt per sq metre as I understand it.
Originally posted by TheHeretic: JL - As the concentration of CO2 in the atmosphere increases, the marginal ability to absorb heat decreases rapidly. Therefore more of the "excess heat" should escape into the upper atmosphere and away. -
This is sometimes claimed on skeptical websites, but there's no credible scientific basis for it. You certainly won't find any peer-reviewed scientific papers that support this assertion.
I thought it was well established that the absorption of infrared radiation was a logarithmic function.
I thought it was well established that the absorption of infrared radiation was a logarithmic function.
The absorption spectrum is well known and the factors are included in climate models. I do not know the details, but additional heat would broaden the spectral lines which will increase the maximum radiation that can be absorbed.
