You are being ridiculous, again.

Mike

That was just before it all blew up in their faces because it was found that CO2 is a lagging indicator of warming and not a cause — a point which you are determined not to address.

I've addressed this point repeatedly in comments in Discussion. As you would know if you took the trouble to read what I say, for example to you, directly, on Aug 7, 2012 at 9:05 PM.

I thought we'd sorted this out :-)

The CO2-warming lag during deglacials doesn't 'falsify' anything. CO2 is a feedback to the initial orbital forcing. Hence the lag. Its effect is to amplify the initial forcing (it's a positive feedback) which makes CO2 a necessary part of the process that leads from orbital forcing to interglacial. The process itself is a demonstration that feedbacks net positive.

One of the interesting things about orbitally forced deglaciation is that the total amount of solar energy reaching the earth's surface is barely increased. Yet it's enough to end an ice age. It's the *regional and seasonal* effect that triggers melting of the NH ice sheet which gets the feedback ball rolling. Just increased summer insolation at high Northern latitudes. How could this end an ice age unless feedbacks net positive?

Put another way, how can an insensitive climate system dominated by negative feedbacks behave like earth's climate system under these circumstances?

This is one of the many non-joys of 'debating' with 'sceptics'. You explain stuff, and five minutes later the same old crap comes round on the carousel again. Ad infinitum. Ad nauseam. And

Now do you understand this point, finally? Nobody argues that CO2 terminated glacials. That is a straw man. During deglaciation, CO2 is treated as a *feedback* to the initial orbital forcing. A feedback. Okay? So it *lags* the original forcing. Okay?

So the 'sceptic' argument about CO2 lagging T during deglaciation 'falsifying AGW' is a perversion of the actual scientific perspective. Aka complete crap.

Sorry Mike, but as for the rest of the tripe about 'Santer is evil' and 'what is the scientific mainstream?' and 'have they looked for anything else?' - it's not worth a response. If our roles were reversed, and this was a mainstream rather than a contrarian blog, I would suspect you of trolling.

Not a single word of that quote is empirical evidence that CO2 causes warming.

You might want to go back to the discussions upthread and on the 'best evidence revisited' thread about the relationship between CO2 and T over deep time (eg the entire Cenozoic).

As I said to Philip earlier, it all fits together.

"It all fits together" is not empirical evidence. It's hand-waving.

And you are doing what, exactly?

:-)

If you know of any evidence that the major change in forcing over the Cenozoic *wasn't* CO2, please share it.

Mike

I am not going to dispute your second paragraph because I don't know whether you are correct or not.
And neither do you.

Here's what I take it we are talking about:

One of the interesting things about orbitally forced deglaciation is that the total amount of solar energy reaching the earth's surface is barely increased. Yet it's enough to end an ice age. It's the *regional and seasonal* effect that triggers melting of the NH ice sheet which gets the feedback ball rolling. Just increased summer insolation at high Northern latitudes. How could this end an ice age unless feedbacks net positive?

Put another way, how can an insensitive climate system dominated by negative feedbacks behave like earth's climate system under these circumstances?

It's like holding one of those little geography class globes near a desk light. If you tilt the axis a bit you can increase the intensity of light up near the top without increasing the *total amount* of light falling on the globe as a whole.

The key thing here is that the degree of axial tilt varies slowly but cyclically over time (the obliquity cycle).

The earth's orbit around the sun also gradually varies between circular and slightly elliptical, but again the cycle is regular (orbital eccentricity).

Put the two consistently repeating but different cycles together and roughly every 100,000 years summer insolation at high northern latitudes peaks. But *total* global insolation rises only slightly.

The peak summer orbital forcing at high NH latitude apparently initiates glacial terminations by melting and destabilising the NH ice sheet. But it is not sufficient to account for the full warming that occurs during deglaciation. This requires a synergy of positive feedbacks - or a healthy peck of fair dust. Otherwise, nothing much could happen and the climate system would have got stuck in a glacial state.

Orbital dynamics is pretty iron-clad, which leaves us with positive feedbacks and a moderately sensitive climate system.

I can see that I haven't yet explained this to your satisfaction, so I hope this helps.

Odd. You skipped a whole comment there. See Aug 14, 2012 at 10:30 PM.

Just how many more times do I have to ask you to show the empirical evidence that it was?

Follow the references in HS12. Are those reconstructions of paleoatmospheric CO2 wrong? Why? Where's the evidence?

This whole discussion is the one of the insane ones I've read - not counting sane participants.

The evidence from paleoclimatic reconstructions spanning periods encompassing millions of years a stretch, is used as the basis for firm predictions of what will happen in the coming few years. This is the definition of madness.

Aug 15, 2012 at 3:52 AM | shub>>>>>

We should be used to BBD's trolling techniques by now.

There is NO empirical evidence for any of his assertions repeated ad nauseum.

He just likes to make a lot of noise and arguing with him just encourages him further, as with his new best friend Philip - who I don't recall seeing till a couple of weeks ago.

Everything BBD says is pure speculative garbage. He calls himself a sceptic regarding climate discussions and then plays chief groupy to his hero Hansen.

In fact, he'll say anything at all to get the response his narcissistic ego so craves - ignore him, he's just another version of ZDB.

As I've tried to point out several times, it is not plausible that the Milankovitch effect is directly responsible
for the glacial transitions, with or without help from CO2.

Aug 15, 2012 at 9:30 AM | Philip Richens>>>>

So what do you suggest IS responsible?

Philip

As I've tried to point out several times, it is not plausible that the Milankovitch effect is directly responsible for the glacial transitions, with or without help from CO2.

See Shakun et al. (2012). Warning: people who insist that CO2 lags T during deglaciation are going to have an unpleasant surprise. Those with open minds simply wondering *how* high-latitude NH forcing triggers deglaciation will find much of interest.

This is why the naïve invocation of orbitals is certainly incorrect.

You are in the minority there, so a little less certainty would be appropriate. It's interesting to see the rise of 'Milankovitch denial' hand in hand with elephant blindness though.

Mike

The point here is not what caused warm periods (which were probably not globally synchronous anyway) this side of the Holocene Thermal Maximum. The problem is what happens when you increase CO2 forcing in a demonstrably sensitive climate system.

Energy begins to accumulate, both in the oceans and the atmosphere. Natural variability continues, as does negative forcing from anthropogenic sulphate aerosols, but the CO2 signal slowly begins to emerge. The results look like this.

This discussion has taken in three general things: the relationship between CO2 and T over *deep time*; the demonstration that the climate system is at least moderately sensitive (which *requires* that feedbacks net positive) and the implications this has if CO2 forcing is substantially increased.

Argue with the physics all you like; it's foolish and it changes nothing. You are surrounded by empirical evidence that CO2 forcing is causing energy to accumulate - slowly at present - in the climate system. Have a look at Arctic ice, or the latest about the Greenland Ice Sheet, or check up on permafrost melt - google is your friend. The evidence - solid, empirical evidence - is everywhere. Only you refuse to see it. And I can't help you with elephant blindness I'm afraid.

shub

It is the same crap propaganda from science communicators. Don't recycle them.

Got any examples of your own?

Eh? This *was* my own example. If you have an example of it being used elsewhere, please link. I'd be interested to see. You aren't by any chance just saying *anything you can think of* in an attempt to delegitimise me, are you? I'm shocked, I tell you, shocked.

Although not as much as I was by this:

If the earth tilts a 'little' - just as our friend here quotes from his catechism - does that produce a 'small' change in forcing?

That's *proof* that you have completely failed to understand Milankovitch forcing, despite repeated explanations. You should be embarrassed.