You have an excellent summary. The only points I would take issue with are the criticism of the paleoclimate findings and the comment that there have been no breakthroughs in climate science during the past five years.

While you are probably more familiar with the National Academies assessment than I am, my impression is that they did endorse the interpretation that the warmth of the last half century is unusual. This is not exactly the same thing as accepting without question the specific model of the "hockey stick" presented in 1998 by Mann, Bradley, and Hughes. Even those authors have admitted deficiencies in their original approach to combining proxy data with historical and instrumental records.

Extending back to AD 1300 is new in AR4 and does reflect significant improvements in paleoclimate reconstructions, particularly the sampling resolution for ice cores. I also think the separate consideration of methane is a "breakthrough" of sorts that will continue to be very useful.

The biggest breakthroughs that I have seen are in extending detailed paleoclimate reconstructions back even further, particularly into the Tertiary for the Arctic. We now know that the Arctic was completely ice-free following the Paleocene-Eocene Thermal Maximum (PETM). That may not be on the front burner for those blogging about anthropogenic global warming, but it does have some huge implications. We are also starting to understand how rapid melting of ice sheets played a role in many of the Quaternary interstadials and "Heinrich events."

Sean-

I think you're confusing two things:
the Earth has been warming for at least 500 years, and perhaps 1000 or more.  This is discussed on the top half of page 8.

We can (mostly) attribute warming over the last 50 years to humans.  This is discussed at the bottom of page 8.

Hope this helps clarify what I said.

In discussions surrounding the new IPCC report, I have found there are people that want an "extremely likely" or "virtually certain" degree of confidence that human activities have caused global warming before they act, citing the major economic and corporate shifts required.

Although an argument could be made that shifting from fossil fuels has many other advantages along with mitigation of global warming, the fact that science can not always deliver a 99% confidence level, particularly for complicated systems seems to cause hesitation for some to act.  Perhaps it is a lack of scientific understanding of risks, a stricter observance of the precautionary approach, or maybe it is just another way of staying in denial.

In any event, could you please provide a few examples of other issues where the scientific degree of uncertainty was 90% or less.  I think placing the 90% certainty in context would help those outside of statistics appreciate that societies have made major decisions based on a lesser degree of certainty in the past.

Glad I found this site, and you folks, with all your opinions. As the chief wrangler of the brand-new Great Green America Fest (dot com) we're trying to gather as many sources as we can to offer the patrons here (in July 2007) as many opportunities as we can for them to learn on their own, for their own futures.

I mostly studied beer for the past 50 or so years, but then, as we say in Zen, "I woke up."

Thanks, all, for being here and giving a damn. Feel free to email me some ideas, observations, whate'er!

Glad I found this site, and you folks, with all your opinions. As the chief wrangler of the brand-new Great Green America Fest (dot com) we're trying to gather as many sources as we can to offer the patrons here (in July 2007) as many opportunities as we can for them to learn on their own, for their own futures.

I mostly studied beer for the past 50 or so years, but then, as we say in Zen, "I woke up."

Thanks, all, for being here and giving a damn. Feel free to email me some ideas, observations, whate'er!

Hey, I just made a correlation.    There are more scissors in the world than ever before.   Because there are more people, there are more scissors in the world...and many of them are still the old fashioned kind (without the big plastic handle that us left handers can't use).

It's a direct correlation with Global Heating.

Oh yes, in the Renaissance,  there was  brief Heating Period, and scissor production fell -- but records were sketchy then!

I am running a new Intergovernmental Panel on limiting scissor production....this will then cause us not to heat up so fast.

Andrew,

Thanks for the clarification.  Alles Klar.

Sean

If the police had a tip-off about planes flying into the World Trade Center, I would expect them to act, even if the likelihood of the tip-off being accurate were only 1%.

If scientists were sure that there were a 10% probability of a known asteroid obliterating all life on earth in 30 years time I would personally be prepared to undergo a fair deal of financial hardship to avoid that event even though 9 out of 10 times that effort would be wasted. I mightn't be willing to work in a salt mine in Siberia for the next 30 years but I would be willing to take a hit on my "quality of life" by spending time and money avoiding that possibility.

So should we be willing to act upon global warming when the probability of it being man-made is (properly) 92.5%, by IPCC judgment, and it may not hit us fully for quite some time. It will not be a catastrophic event like the asteroid and there is a 7.5% chance that we will be wasting our time.

To me, my decision depends on a trade-off between, on the one hand: how much I value the world as it is against the world as it will become with accelerating global warming and on the other hand: how much I value the other things I could do with my time and money if I were not preoccupied by this issue.

 From what I have read, if you change your level of income, either up or down, you may find it pleasant/unpleasant for a while but after that you adjust your expectations to your new circumstances and are just as happy as before (as long as your income doesn't drop below the poverty line). Furthermore I believe that if others are also making a sacrifice then a cut in income is more tolerable (as happened during WW II).

So I am not impressed by the argument that we shouldn't act because we will take an economic hit (though I agree that Ethiopians could validly make such a claim). I am also not impressed by the economic argument because there is a 92.5% probability that I have (unknowingly) bought my ease and wealth at the future cost of Ethiopians, Chinese peasants and the like.

A further argument for inaction I have heard is that money spent on global warming would be better spent on helping the world's poor directly, ie via charity. I can't see the relevance of this. I am not acting out of charity by spending money on global warming (although my actions will indirectly help poor countries). By tackling global warming I am really acting in my own self-interest to maintain the world as it is because I value (and hopefully my children will also value) its diversity of wildlife, etc. So any money devoted to global warming should come out of selfish expenditures - my priority would be various subsidies, defence expenditure, etc which have no relevance to charitable funds which should logically remain unaffected.