"1) During previous interglacials, CO2 levels declined after peaking at higher/equivalent levels than our present level"

— Do you have a link for this? As far as I know, we are at the highest levels of Co2 in a million years or so. It takes GEOLOGICAL time to get to higher levels than today.

2) "mystery sink"

— Thank God it is there, and move on to how we can reduce Co2 because despite its existence we're STILL too high for safety! (However, I bet you it has something to do with charcoal in forests absorbing Co2 as it becomes a home to growing fungi).

"3) I have read, and others have posted, that the effectiveness of CO2 as a greenhouse gas declines 'exponentially' with its concentration and that current CO2 levels already trap most of this radiation and further CO2 will have very little effect - like further coats of black paint on a window (as another poster described it). To what extent is this true?"

— I don't pretend to do the math or physics myself, but check this out.
http://www.scienceforums.net/forum/showpost.php?p=498994&postcount=46

"So one problem here is that the values are presented on a graph with a linear scale, when the effects are not linear. A change from 200 ppm to 1000 ppm of CO2 is going to have the same effect on forcing as the increase from 1000 ppm to 5000 ppm. An ideal blackbody at 295K radiates almost 15% more energy than one at 285 K, even though that's only a 3.5% increase in temperature."

1000ppm is game over! (We need to be under 350).

4) "Opportunity cost"
Please watch this argument (by a science teacher).
http://www.youtube.com/watch?v=zORv8wwiadQ

1. Opportunities? Discover if we can be energy secure, clean (free of coal mercury pollution), and run a society without fossil fuels before we RUN OUT!

2. Stop paying people we don't like very much for oil?

3. If we stopped paying $10 billion in subsidies a year to fossil fuel companies, renewables would be ECONOMICALLY competitive! Our coal is ARTIFICIALLY cheap! Point 2:
http://eclipsenow.wordpress.com/2007/06/10/refuel-on-renewables/

Excellent post Eclipse.

Will respond more fully over the weekend, but in the meantime:

1. Sorry, forgot to update for my realisation that CO2 levels have not been this high for millions of years (further reading reveals that there is some variation between studies as to CO2 levels over geological time, but it definitely seems we are at least close to the highest CO2 levels in millions of years.

Nevertheless, even if the higher CO2 levels occurred millions of years ago, the question is still relevant.. why was there no runaway greenhouse effect back then?

2. While you may be right about the mystery sink... "thank God..." this clearly demonstrates a big hole in our understanding of the CO2 system.

3. You said "1000ppm is game over" - maybe you are right about this, or maybe not. That's kind of the point of this excersise for me.

The graph you linked to is very interesting. Shows a much weaker correlation between CO2 and temp than the Vostok ice cores (which cover only relatively recent history).
Will do some more reading on this before I comment further.

4. Interesting video. Basically uses an argument I found very pursuasive for a time, but which I now see as flawed. Deserving of its own post in reply, but in short he does not properly deal with opportunity cost, and IMO misrepresents the alternatives.

More later.

4.1 Totally agree with this argument.

4.2 Ditto.

4.3 Think this is an overstated issue. The figures don't show that the price of fossil fuels is significantly cheaper because of subsidies.

Will post more on this later, but again, thanks Eclipse for having a stab at my questions. Some food for thought.

“Nevertheless, even if the higher CO2 levels occurred millions of years ago, the question is still relevant.. why was there no runaway greenhouse effect back then?"

Kalin1

In an earlier post, I advised there was a runaway greenhouse effect “back then,” therefore where is your evidence to support your reiteration? I also suggested you access palaeontologist, Dewy McLean’s hypothesis on the K-T extinctions to which you responded:

“My point was that there was no runaway greenhouse gas effect despite higher CO2 levels. I am aware of no widely accepted theory that explains why increased CO2 levels today will cause a runaway effect, but did not during previous periods of high CO2. The question of past extinctions caused by climate change or CO2 concentrations is not relevant to the runaway greenhouse effect issue (though I will try to read up on Dewey McLean's hypothesis when I get a chance.”

Please note that Dewey's McLean's apolitical research commenced in the 70’s – well before any public debate on climate change:

http://74.125.153.132/search?q=cache:6-zo_Ic1mTYJ:filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/pages/studentv.html+dewey+McLean,+dewey+Volcanism-induced+trans-Cretaceous-Tertiary+disorganization+of+the+biosphere:&cd=3&hl=en&ct=clnk&gl=au

You claim that the current greenhouse effect is irrelevant to one that could be caused by a volcanic eruption. Why is that? Both anthropogenic and natural causes of hazardous emissions can change the biosphere from orderly to chaotic.

One can only hope that the planet does not decide to deal humans a natural catastrophe when humans already emit massive amounts of CO2 on a daily basis - impacting on the biosphere’s equilibrium.

You appear not to have any interest in the empirical evidence of man's carbon footprint - the rapid species extinctions, emerging zoonotic diseases, chronic dryland salinity, soil degradation, increased cancer rates in humans and animals, atmospheric and ambient air pollution, dead trees, mass fish and bird deaths, forest depletion and toxic (ie. hydrocarbons etc), dying rivers in Australia.

Feel free to deny any relevance between climate change and anthropogenic causes, but please provide another theory. However, unless you are totally oblivious to the state of Australia's environment, I daresay you would be hard pressed to provide a credible theory that lacks any anthropogenic cause and effect.

Good revision of the conversation there Proto. I also referred Kalin to the ABC's "Crude" super-greenhouse effect which was quite severe and out of control compared to today's climate, so I don't know why Kalin keeps saying the climate never 'ran away' before, just look at the ELE wiki I referred to earlier!

Also different, modern civilisation is here this time. We want to support the 6.5 billion of us on planet earth. We also NEED to preserve biodiversity and ecosystem services which are of unmeasurable economic value.

So here's the challenge, in previous climate shifts trees and plants and their accompanying animal and insect species gradually migrated into the more comfortable zones. As some areas warmed, seeds sprouted there that had never grown before and the forest 'moved'. As those areas then later cooled again a hundred thousand years later, the cooler species took over again.

How do ecosystems migrate with our cities and agriculture in the way? We've created artificial "ecosystem islands" surrounded by unfriendly "oceans" of us! We're going to have to pay biologists and ecologists to relocate ecosystems! "Ecosystem parks" will start to emerge. This is already being discussed in the Australian scientific community. Imagine the expense!

However, as this is occurring much faster than most gradual climate shifts in the past, even the wilder ecosystems NOT surrounded by us are having trouble adapting fast enough. Flannery documents the loss of the golden toad as one of the first climate change extinctions. He used to visit the site as a field biologist.
http://en.wikipedia.org/wiki/Golden_toad

But again, back to more selfish questions. All those glaciers we see retreating across the roof of the world? What happens when 1 to 2 billion Indians and Chinese begin to starve?
http://www.earth-policy.org/Updates/2008/Update71.htm

Conservative:
What’s your view on global warming?

“I don’ think we have anything to worry about with this 23 year old global warming stuff because old Mother Nature is going to do what it’s going to do, the way it’s always done it before and we can’t stop it, no way. Volcanoes, fossils and comet-hits come to mind? Let’s continue taking care of our planet and progress to making life even better for more people of the world.”

Liberal:
What’s your view on global warming?

“Well I suppose we must be doing something to our earth. You can’t deny that. That’s obvious to anyone. Just look around and see the garbage and the dirty air and our polluted seas and lakes. And what’s wrong with helping the planet anyways? We can’t just keep doing what we do to the planet forever like this. Sooner or later it’s going to catch up with us. We are obligated to leave this planet in good shape for our children. And it’s better to be safe than sorry.”

MeMe,
Conservative in 50 years:

"What, we're at war with China and India? What food crisis? Why didn't the scientists TELL US the glaciers were retreating? What, I thought that global warming thing was a myth... WHAT? They could MEASURE the heat Co2 traps, and CALCULATE HOW MUCH EXTRA ENERGY WAS BEING TRAPPED? WHY DIDN'T ANYONE TELL ME!? Oh really? And us non-scientists were supposed to BELIEVE them!? No, I'm not an expert on climatology but I just thought.... what's that bright light? bzzzzzzzz..........."

But that's a cheap shot and is basically not really relevant.

I know this is real hard for you MeMe but physics and chemistry are not really all that political. They'll just do their thing even if you voted Sarah Palin in as President for life of the good old boys "Joe-6-pack club" wink wink.

Yes nature could wipe us out.

Yes it has dumped heaps of Co2 into the atmosphere in the past.

And YES you obviously HAVEN'T read any of the recent posts because we've just covered all that!

You've again proved what a non-engaging trolling retard you truly are. If this site were properly moderated you'd have been banned about 20 pages ago. I've seen it happen before. At this point I don't care if I get a ban for crankiness, because unmoderated sites are often just not worth belonging to.