Freeman Dyson (the smartest man in the world, still) published a reproof in the Boston Globe, chiding the Paris Conference and attendees for believing that "the science is settled":

The IPCC believes climate change is harmful; that the science of climate change is settled and understood; that climate change is largely due to human activities, particularly the release of carbon dioxide into the atmosphere by industrial societies; and that there is an urgent need to fight climate change by reducing the emissions of carbon dioxide.

Ten days later, the Globe published a scolding reply to Dyson by two MIT professors, co-signed by another six.  This alleged that "[s]o much more is understood about climate change than skeptic admits," expressing their dismay at the ignorance and naiveté of Dyson, poor clod.

The following questions should be addressed to the MIT chaps, and there are footnotes for those less specialized:

1. If the surface temperature of Venus is completely explained by the adiabatic lapse rate (1) of its atmosphere, 92 times thicker than ours, then why isn't our surface temperature explained the same way?  If you replace our atmosphere with 100% nitrogen, the math works out the same.

2.  Granted that water vapor and the other GHGs have some effect (2), why don't they correlate – at all – with the major swings in climate over the past 3 million years?  The end-Ordovician (Hirnantian) Ice Age, 440 million years ago, began when CO2 was around 4,000 ppm and lasted a few million years.  At the end of that time, with 85% of marine life extinct, when the frigid oceans had gobbled up atmospheric CO2 to around 3,000 ppm, the globe suddenly began to warm up, getting back to the previous 22°C with astonishing speed.  You haven't the faintest idea why it cooled so fast and so far, or why it warmed so fast and so far.  After all, that was the time of the cool(er) young(er) sun.  It's not just The Pause that doesn't fit your model.

3. The Earth has spent half of the previous 600 million years around 22°C, which makes it look as though there's a tight lid at that number.  Why doesn't that entail strong negative feedback and no "tipping point"?

4. We don't know why the P-T extinction (3) warming (to at least 28°C) occurred so fast, nor why it was so brief.  What brought the temperature down to 22°C again?  Why didn't it "run away"?

5. Why is the lowest temperature around 12°C?  When "snowball Earth" occurs, with glaciers almost down to the equator, why doesn't the albedo (4) force more cooling, more ice, more reflectance, and more cooling down to the Stefan-Boltzmann equilibrium (5) of 255°K (0°F)?

6. In other words, why has the Earth's temperature been so stable, ranging from 285°K to 295°K since the end of the Hadean Age 3 billion years ago?  That's a median of 290°K (62°F), ±2%.  Climate stability needs an answer, not climate change.

7. If CO2 is close to saturated right now, and its effectiveness declines logarithmically, why is it dangerous to produce more?  After all, it's currently close to the lowest it's been for the last 600 million years.

8. If it's suspicious for skeptics to get paid by Big Oil (they wish!), why isn't it suspicious for you to be paid by grants from governments who want to tax and spend?  Weren't the Climategate emails enough evidence for you?

Dyson's point is not that he knows the answers.  His point is that you don't even know that you don't know the answers.  Here he discusses CO2.

Best of luck with your grants.

(1) Adiabatic refers to temperature change without addition or subtraction of heat (energy), as when compressed gas gets warm and expanding gas gets cool.  Thus, the Earth's air temperature varies directly with altitude (the lapse rate), about 3°F per 1,000 feet.

(2) Greenhouse gases absorb infrared radiation at different wavelengths with varying potency, and then immediately re-radiate in all directions, including down.  Their major effect is to cool the stratosphere.

(3)  As the Permian Ice Age was ending 250 million years ago (Fig.1), temperatures rose fairly rapidly to the 22°C "lid," then suddenly exploded to 28°C (82°F) or more, very briefly, causing the extinction of 60% (land, including most insects) to 90% (marine) species.  Ancestors of the dinosaurs and of mammals, among others, survived.  That was the only time that average global temperature exceeded 22°C.  The current average global temperature is 15°C.

(4) Albedo is the reflectance of a surface, about 0.9 for fresh snow and 0.07 for charcoal.  Venus's albedo is about 0.75, making it the brightest object in the sky other than the moon.  Earth's 0.3 is mostly cloud, ice, and snow.

(5) The Stefan-Boltzman equation can be used to calculate the sun's input and the earth's output radiation at equilibrium: 6°C for a perfect black body or, allowing for Earth's albedo of 0.3, -18°C or 255°K

Addendum: The 2012 annual meeting of the American Meteorological Association had several members addressing the idea that "CO2 does not drive the Earth's climate," including this one.

Images have been updated.  —Ed