Anthopogenic Global Warming Myth or Real ?

DogB said:
But how does the trigger overcome all the positive feedbacks. The world is set to 'hot'.There's little arctic ice and snow to reflect the sunlight, there's heaps of CO2 and methane to trap the heat.

These are powerful effects. Any trigger event must be massively powerful to overcome them - correct?
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Nope. The trigger doesn’t need to overcome the feedback because the feedback amplifies whatever the trigger is doing.

Lets say the earth has finished it’s warming in response to the forcing that occurred and then the forcing is backed off a bit. In this case you get a small amount of cooling that cases the oceans to absorb CO2, less CO2 in the atmosphere cools the earth further, causing the ocean to absorb more CO2. IOW you have the same positive feedback pushing temperatures down.

As I said before there is some hysteresis, but it can’t be insurmountable otherwise the small effect of Milankovic cycles wouldn’t be able to kick us in and out of glaciations.
 
DogB said:
That requires a cooling forcing to be able to overcome all of the positive feedbacks.

If a change in Milankovich phase is sufficient to trigger a cooling even in spite of all the forcings opposing, why isn’t a Milankovich phase change sufficient to cause all of the warming phase without the influence of CO2 at all?
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Again, positive feedback amplifies whatever the forcing is doing. If there is any drop at all in the forcing (negative forcing), the positive feedback amplifies it.
 
lomiller said:
Nope. The trigger doesn’t need to overcome the feedback because the feedback amplifies whatever the trigger is doing.

Lets say the earth has finished it’s warming in response to the forcing that occurred and then the forcing is backed off a bit. In this case you get a small amount of cooling that cases the oceans to absorb CO2, less CO2 in the atmosphere cools the earth further, causing the ocean to absorb more CO2. IOW you have the same positive feedback pushing temperatures down.

As I said before there is some hysteresis, but it can’t be insurmountable otherwise the small effect of Milankovic cycles wouldn’t be able to kick us in and out of glaciations.
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I know I'm slow but bear with me. I don’t want to put words in your mouth so I’m going to make sure I understand your point.

What you’re saying seems to me to imply some sort of steady ‘warm’ state at which the warming trigger is still operating yet the other positive feedbacks have maxed out and are not continuing to force the temperature higher.

Is that correct?
 
CapelDodger said:
I'm reminded of Tom Lehrer's comment that he was giving up satire because Kissinger got the Peace Prize. There's no room left for satire or parody to work in.

No parody could be more locked onto the Red Threat than Munchkin explicitly is. No parody could be more verbose and clunkingly faux-Classicist. No parody could be more self-basting. No parody could make a more laughable scientific case in all seriousness.

Real people can, of course. Miskolczi is in contention, and Douglass and Christy have just appeared in E'n'E with a show-stopper of a paper which everybody has to address before climate science can possibly move on. It is sad, despairing stuff to which nobody of note pays any attention.

The right is pulling its people and funds out of AGW. They've lost that. They need to concentrate on why the financial crisis is not the fault of the markets but of governments, and Bill Clinton in particular. Notice how quiet it's gone on this front since early September? Even mhaze is just phoning it in; I had to bring up the Douglass and Christy thing myself.
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Do you make sure you say your daily prayer?

The shortest but most heartfelt of our daily prayers has
just three words: “God bless America!
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DogB said:
What you’re saying seems to me to imply some sort of steady ‘warm’ state at which the warming trigger is still operating yet the other positive feedbacks have maxed out and are not continuing to force the temperature higher.
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No the warming trigger/forcing is not still operating, so the positive feedback has also stopped operating. The world is in equilibrium. Temperature and CO2 levels are constant. Then another forcing/trigger (warming or cooling) begins, e.g. another change in the earth's orbit, and the positive feedback of the CO2 amplifies it.
 
DogB said:
I know I'm slow but bear with me. I don’t want to put words in your mouth so I’m going to make sure I understand your point.

What you’re saying seems to me to imply some sort of steady ‘warm’ state at which the warming trigger is still operating yet the other positive feedbacks have maxed out and are not continuing to force the temperature higher.

Is that correct?
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I think a big point that has to be made is that positive feedbacks do not necessarily equate to runaway warming. In its basic form, a positive feedback (such as the oceans releasing CO2 in response to warming) merely serves to amplify a forcing (such as a Milankovitch cycle at the end of an ice age) so that when the earth reaches equilibrium in response to said forcing, it does so at a higher temperature than it would have done otherwise. If you were to take away the original forcing (say by the cycle coming around), the amplification would also be taken away, so you'd be right back where you started with the earth at its original temperature.

The whole 'trigger' or 'tipping point' relates to a hysteresis in the feedbacks (say due to ice coverage). This means that the net feedback is suppressed to an extent until the temperature reaches a critical point. When it reaches this point, the total feedback suddenly increases and therefore the equilibrium temperature jumps up. However, similar logic regarding restoration still applies; if you were to reduce your forcing, you would go back down the other side of the hysteresis curve until you reached another (lower) critical temperature, at which point, the system would tip back in the opposite direction and the feedbacks go back to the way they were and you could return to where you started again.

The iffy bit with today's situation is where our comfort zone exists with respect to this hysteresis. A worry is that if the earth as we know and love it is in a metastable state, once the tipping point is reached, we won't be able to get back to where we were without going through a phase of extreme cooling first (which would, in effect, reset the feedbacks).
 
DogB said:
Don’t they remain warming feedbacks until the cooling begins?

The oceans have to cool. They have to cool while the CO2 is still in the atmosphere, while the methane is as well, while the Arctic remains ice free.

That requires a cooling forcing to be able to overcome all of the positive feedbacks.
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No, the positive feedbacks apply to the cooling forcing. "Forcings" and "feedbacks" are quite different things : feedbacks only exist in regard to a forcing, they have no independent existance.

Consider the Milankovich cycle. When it enters a warming phase the planet warms up accordingly and feedbacks (positive and negative) influence how much it warms. Eventually the Milankovich cycle reaches a peak; at this point there is no forcing and no feedback. The planet is at equilibrium. CO2 still has the effect of keeping the planet warm, but it's a constant effect because the CO2 level is constant.

Then the cycle enters its cooling phase and the feedbacks start up again. The oceans cool a little and take up more CO2; ice and snow-cover expand a little and albedo goes up. Gradually a new glaciation builds.

(Glaciations form more slowly than they end because it's physically easier to lose ice than it is to gain it. When ice melts gravity carries the water away, but for ice to form water-vapour must first be lifted against gravity to get it out of the oceans. But that's something of a digression. The feedbacks are the same in both cases.)

If a change in Milankovich phase is sufficient to trigger a cooling even in spite of all the forcings opposing, why isn’t a Milankovich phase change sufficient to cause all of the warming phase without the influence of CO2 at all?
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All becomes clear by distinguishing forcings from feedbacks.

The Milankovich cycle cannot of itself cause interglacials (even with albedo feedback) because its effect is too slow. The warming phase would be over before it had any significant impact. That was the theory's big problem before the CO2 and H2O feedbacks were recognised.
 
DogB said:
I know I'm slow but bear with me. I don’t want to put words in your mouth so I’m going to make sure I understand your point.

What you’re saying seems to me to imply some sort of steady ‘warm’ state at which the warming trigger is still operating yet the other positive feedbacks have maxed out and are not continuing to force the temperature higher.

Is that correct?
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That’s pretty much correct. Systems with positive feedback generally either blow up, oscillate or converge to a final value depending on the amount of forward open loop gain and the feedback ratio.


Since there is no forward gain in the climate system, it's normally stable unless you hit a situation were the feedback ratio is large. I.E. you hit a range where a very small increase in temperature could release a large amount of CO2 or Methane or a small drop in temperature could cause a large amount of CO2 to be absorbed.

After you hit one of these non-linearities it is harder to go back the other way. If we manage to thaw the permafrost in Siberia, forcings would have to drop below current levels just to bring temperatures back down, and with forcings below current levels it's possible temperature could keep going down until there was a complete glaciation.
 
That actually makes perfect sense!!!! So much so that I actually feel a bit of a goose at the moment.

Thank you all for your patience and reasoned conversation.

I must admit I’m not so happy to have my comfortable sceptic bubble burst but the truth must out. So tell me, what should I be doing to prepare? I live 30km and 55metres elevation away from the ocean. I live in a subtropical city (Brisbane, Australia) in a robust (cyclone rated) modern house.

Should I be worried about anything in particular?
 
DogB said:
That actually makes perfect sense!!!! So much so that I actually feel a bit of a goose at the moment.

Thank you all for your patience and reasoned conversation.

I must admit I’m not so happy to have my comfortable sceptic bubble burst but the truth must out. So tell me, what should I be doing to prepare? I live 30km and 55metres elevation away from the ocean. I live in a subtropical city (Brisbane, Australia) in a robust (cyclone rated) modern house.

Should I be worried about anything in particular?
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It's great to see reasoned questions. I am strictly an amateur at this, and it is amazing the breadth of knowledge required to understand this complex topic. Also great to see some very informed people contributing to these threads.
 
DogB said:
That actually makes perfect sense!!!! So much so that I actually feel a bit of a goose at the moment.

Thank you all for your patience and reasoned conversation.

I must admit I’m not so happy to have my comfortable sceptic bubble burst but the truth must out. So tell me, what should I be doing to prepare? I live 30km and 55metres elevation away from the ocean. I live in a subtropical city (Brisbane, Australia) in a robust (cyclone rated) modern house.

Should I be worried about anything in particular?
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IIRC, most people seem to think Australia in general is likely to get hotter and drier. However, once you go beyond simply saying 'the world is going to heat up', the predictions start to get less and less certain, especially when you want to know about weather patterns. For instance, predicting the effect of climate change on storm frequency and severity, while being a worthy topic of research and good headline-grabber to boot, is far from being an exact science right now.
 
http://news.bbc.co.uk/1/hi/sci/tech/7692963.stm

"The team from the university's Centre for Polar Observation and Modelling - part of the UK's National Centre for Earth Observation - found that last winter the ice had thinned by an average of 26cm (0.9ft) below the 2002-2008 winter average.

Dr Giles added that the data also showed the western Arctic experienced the greatest impact, where the ice thinned by up to 49cm (1.6ft)."

I know this is from the loony BBC, but it appears to have some data.
 
DogB said:
That actually makes perfect sense!!!! So much so that I actually feel a bit of a goose at the moment.

Thank you all for your patience and reasoned conversation.

I must admit I’m not so happy to have my comfortable sceptic bubble burst but the truth must out. So tell me, what should I be doing to prepare? I live 30km and 55metres elevation away from the ocean. I live in a subtropical city (Brisbane, Australia) in a robust (cyclone rated) modern house.

Should I be worried about anything in particular?
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The biggest threats you face are probably drought and economic disruption resulting from issues at cities closer to sea level. As Spud1k says, there a lot more questions around regional projections then global ones. There is increasing confidence in continental scale projections but take anything below that with a grain of salt..

Barring something like a major release of CO2/Methane from the Artic we are looking at the loss of about half the ice in West Antarctica and Greenland over the next few centuries which amounts to about 6m so you are in no particular threat from sea level rise. To get 50m most of Antarctica would need to melt, which would probably take 1000+ years and isn’t currently projected to happen.
 
DogB said:
http://ap.google.com/article/ALeqM5ibwC_yqdCtXd24mBJe6lMkwnUBaAD9415G5O0

I like my steak and I like my flat screen TV. This is getting depressing.
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Move to Ireland, raise cattle, and install solar panels and a windmill. That should cheer you up no end. With lines of supply that short you'll have nothing to worry about.

Except cattle-thieves, of course. The Irish are notorious for that ... Not so much recently, though (the worst offenders were transported, and good riddance, I say).
 
Mr Clingford said:
http://news.bbc.co.uk/1/hi/sci/tech/7692963.stm

"The team from the university's Centre for Polar Observation and Modelling - part of the UK's National Centre for Earth Observation - found that last winter the ice had thinned by an average of 26cm (0.9ft) below the 2002-2008 winter average.

Dr Giles added that the data also showed the western Arctic experienced the greatest impact, where the ice thinned by up to 49cm (1.6ft)."

I know this is from the loony BBC, but it appears to have some data.
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26cm does seem a lot, but I'd like to more context. Such as where that leaves the average - a metre, five, ten?

http://www.nceo.ac.uk/ has a graph of anomalies, which does suggest a plummet. It also contains

"The Envisat satellite that provided the UCL scientists with their data doesn't cover the whole of the North Pole. Because of the satellite's orbit, there's a hole north of 81.5 degrees, which is about 600 miles shy of the North Pole. But a team, including Laxon, at the Centre for Polar Observation and Modelling has designed a satellite - CryoSat-2 - to plug this hole.

CryoSat-2 is the first radar satellite specifically designed to measure ice thickness. It will do this with greater resolution than is possible with Envisat and so will give scientists a much more detailed picture of what is happening to ice in the Arctic. CryoSat-2 is being prepared for launch at the end of 2009. "
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We're soooo going to own Arctic Ice about the time it's not there anymore.
 
Political spin, and affective for most viewers, is "tripe"? I suppose that depends on what you want done.
 
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