Some responses to GrahamY:

"The issue is whether the emissions will cause a catastophe or not, and the empirical evidence is they won't."

Big call. What evidence is that then? Exactly how does it support this conclusion? What kind of impacts do you think qualify as a "catastrophe"?

"...unreliable websites like De Smog, Real Climate Deltoid and Greenfyre"

Really? Do you have compelling evidence to back your assertion that they are unreliable - or is this just repeated as if it were a priori true, just because assorted anti-science denial blogs say so? In particular, what is your objection to RealClimate.org? Given that its authors are actual climate scientists, including some at the top of their field, it plays a highly authoritative role in the discussion of climate - not, of course, comparable to the real scientific discourse of peer-reviewed literature, but orders of magnitude more reliable than profoundly ignorant sites like "Watts Up With That", "Climate Audit", etc etc., which have a long and rich history of being either simply wrong or utterly misrepresenting the science.

"I'm assuming, because there has been no rebuttal in response to my last post that we accept the reality of the Medieval Warm Period."

That would depend on what you mean by the "reality" of the MWP. It appears that there was a Medieval Warm Period in some parts of Europe and North America, sure.

Was the local temperature in those regions higher at that time than now? Unlikely, given the evidence.

Was the temperature across the whole of Europe and North America higher at that time than now? Extremely unlikely, given the evidence.

Was the global temperature higher at that time than now? No way.

Some bedtime reading which might help shed some light on the whole MWP thing:

http://www.realclimate.org/index.php/archives/2009/09/hey-ya-mal/
http://tamino.wordpress.com/2007/10/19/not-alike/
http://scienceblogs.com/illconsidered/2006/02/medieval-warm-period-was-just-as-warm.php

Runner, you're hilarious swallowing the "It's been cooling since 1998 myth". I'd love you to link to a 15 or 20 year trend graph that proves that, rather than the little 4 or 5 year cherry-picking deceit you (and others here) choose is your "god" for this subject. Shame on you for being so dishonest in your handling of the science!

http://www.youtube.com/watch?v=y15UGhhRd6M&feature=related

http://www.newscientist.com/article/dn14527-climate-myths-global-warming-stopped-in-1998.html

http://www.newscientist.com/article/dn17808-climate-myths-any-cooling-disproves-global-warming.html

Also, please explain which climatologists were asserting the world was going to hit an ice age in the 1980s, and what percentage of the climate community these people represented? You read it on some pretty little Creationist blog somewhere did you?

The reality seems to be that the media ran away with a minority view and, shock horror, SENSATIONALISED the story way above its scientific merit. This while the rest of the climate community just sat back and went, "Huh?"

So "tie me to an anthill and smear my ears with jam", it was all media hype and "the public" have a negative opinion of 1970's climatology that's not based on any peer-reviewed reality.

http://www.newscientist.com/article/dn11643-climate-myths-they-predicted-global-cooling-in-the-1970s.html

But then again, "the public" includes 10% of Americans that believe they've been abducted by aliens, a significant population that believe the moon landings were faked, and something like 40% that believe there's a government conspiracy to hold back all the evidence for Young Earth Creationism and the world being under 8,000 years old.

I rest my case.

Again, shame on you for propagating the lies and misinformation of the denial-o-sphere.

Eclipse Now, do you accept that you didn't read the graph correctly and that it shows a medieval warm period?

Matt Andrews, you are looking for the empirical evidence. It is right in front of you. The earth has prospered under higher temperatures and higher levels of CO2. There has been no tipping point because of CO2 at higher levels, and in fact temperatures have been lower with CO2 at higher levels than it is now.

We also know from ice cores that CO2 does not drive temperature significantly because it increases after temperature increase and decreases after temperature decrease.

However, we also know from experimental evidence that CO2 is a greenhouse gas.

With respect to unreliable websites. Greenfyre does not pretend to be anything other than partisan. A good example of Deltoid's lack of credibility is the piece we published from Lambert attacking Bolt for attacking An Inconvenient Truth. It made a large number of factual errors, a number of which were picked up in a British court judgement on whether the film was propaganda.

De Smog specialises in flaming people. For a while, because of its propaganda, I thought that Fred Singer, one of the discoverers of the Van Allen belts was a tobacco industry lobbyist.

Real Climate is a sophisticated astro-turfing operation associated with Environmental Media Services, a PR company that does very well out of spinning environmental causes.

What is your evidence for saying that the Medieval Warm Period was not global? This was accepted by everyone, including the IPCC before Mann's Hockey Stick. Now that the Hockey Stick has been completely discredited the onus is on you to show studies or evidence that say it wasn't global.

The data I referenced says that the temperature was higher than now. On the same page of Wikipedia that Ecplise points to there is also a temperature reconstruction showing that for most of the last 10,000 years it has been warmer than now.

I'm happy to argue the toss with you, but you need to get yourself across the evidence and the arguments first.

“What's your evidence for saying that the Medieval Warm Period was not global?”

Graham – There's ample literature suggesting that the Medieval Warm Period was not global but regional:

http://www.sciencedaily.com/releases/2003/10/031020055353.htm

However, if I were you, I’d refrain from using the MWP as a basis for your GW denial, considering there's limited data currently available on the MWP.

“De Smog specialises in flaming people. For a while, because of its propaganda, I thought that Fred Singer, one of the discoverers of the Van Allen belts was a tobacco industry lobbyist.”

I can fully understand why Q&A becomes frustrated when you peddle such rubbish:

1. DeSmog has a reputation for providing accurate information on climate change

2. Fred Singer IS a tobacco lobbyist:

http://tobaccodocuments.org/pm/2040165576-5577.html

3. To accredit Singer with discovering the VA belts is specious.

4. While Singer was a team member, the Van Allen belts were named after American physicist, James Van Allen, who discovered them in 1958. A Soviet researcher, S Vernov, was also accredited with discovering the outer Van Allen belt, based on data sent back from Sputnik 2.

Only Singer brags of “his” discovery of the VA belts.

5. However, Singer was recognised as being the first to publish predictions on the existence of trapped radiation in the earth's magnetic field and was recognised for his research on rocket and satellite technology, remote sensing, cosmic rays etc.

Unfortunately for your argument, Singer exemplifies the ignorance of rocket scientists who were experimenting with the ionosphere without understanding it.

A mishap took place over the south Atlantic where the Van Allen belts dip towards the earth. The second rocket boost of Skylab produced a large burn, causing a massive ionospheric hole as reported by M Mendillo in 1975. Other ignoramuses we know are the maniacs who detonated over 100 nuclear bombs even before they knew of the role the VA belts played in protecting Earth.

Eighty five year old Singer is a member of the predominantly right-wing corporate funded greed merchants and rampaging eco-vandals who've long been discredited by reputable climate scientists. Alas, those facts completely demolish your credibility Graham.

GrahamY,

"Eclipse Now, do you accept that you didn't read the graph correctly and that it shows a medieval warm period?"
Are we even looking at the same graph!?

You seem to think the graph has proved the MWP to be hotter than today.

Except that it doesn't really SHOW us today... the trends of the last few decades are so condensed that only one real measurement, the black line of the UK met office shows up.

As in, it REALLY shows UP... the black line is off the charts but you can see where the projection ends up for 2004 (marked by *). It absolutely blitzes *anything* in the MWP.

But hey, if you just put your thumb over the last inch of the graph you won't have to admit that unfortunate fact and will have perfected the art of cherry-picking, and be ready for the big leagues, maybe a presentation at the Heartland institute? Sorry about the attitude, but I just can't believe your still questioning me about that graph, I thought you were joking.

http://en.wikipedia.org/wiki/File:2000_Year_Temperature_Comparison.png

Eclipse now, you asked for peer-reviewed evidence of the MWP and I gave it to you. Now you're trying to shift the goalposts. You can't take an instrumental record and splice it onto a reconstruction. That is just bad science. If you want to take the reconstruction up to the present then you have to use the proxies up until the present.

But even if I accept your argument (which I don't) that it is warmer now than the Medieval Warm Period that doesn't negate the Medieval Warm Period. So are you going to admit that there was a Medieval Warm Period or are you going to continue to be a denier?