Dear Lord Stern, In the Stern Review, you say with regard to the Hockey Stick controversy, >>Much discussion has focused on whether the current trend in rising global temperatures is unprecedented or within the range expected from natural variations. … [¶] Climate change arguments do not rest on “proving” that the warming trend is unprecedented over the past Millennium. … However, they [the National Research Council] state that in some regions the warming is unambiguously shown to be unprecedented over the past millennium. Stern Review, Part I, Box 1.1, p. 6. Ignoring that science is never about "proving" matters anyway, you argue that being unprecedented is not determinative. Good. But then you conclude after some discussion and by (peer-reviewed?) authority that the unprecedented warming is unambiguously true. This argument is inconsistent. Further, you rely on the present levels of GHGs being unprecedented: >>Current levels of greenhouse gases are higher now than at any time in at least the past 650,000 years. Fn 5 >>Fn 5: Siegenthaler et al. (2005) using data from ice cores. The same research groups recently presented analyses at the 2006 conference of the European Geosciences Union, which suggest that carbon dioxide levels are unprecedented for 800,000 years. Stern Review, Part I, ¶1.2, p. 2 Assuming your facts were true for the moment, you seem to adopt the argument that because the modern warming and modern CO2 concentrations, in particular, are unprecedented that CO2 is known to be the cause of warming. This is the common error of using correlation in place of modeling cause. In fact before any human influence, the warming dominantly preceded the CO2. Therefore CO2 could not have been the cause, and further the shape of the CO2 increase followed Henry's Law showing that it dominantly came from surface waters. This result validates the model that warming adds CO2 by the mechanism of outgassing, and no reason exists that that process is not on-going in the modern era. Henry's Law demands it be so. Now to the facts: Your statement cited from ¶1.2 is common in the IPCC and peer reviewed literature, but is false without a major qualification. It would be correct to say, Current levels of greenhouse gases AVERAGED OVER A FEW MINUTES are higher now than at any time in at least the past 650,000 years AVERAGED OVER MANY DECADES. Mathematics demands it be so. As you have elsewhere noted, this interval refers to ice core records, and the 650,000 figure comes from the Vostok data set. Ice core analysis releases gas from firn ice, and firn ice requires perhaps as little as 40 years, and more likely 70, to several thousand years to close. This means that the ice core method, actually like all detection and measurement processes, is a low pass filter. All such processes measure the average over the aperture, in both time and space. Ice core data reduction is no exception, and is extraordinarily slow. This applies not only to the greenhouse gases, CO2 in particular, but also to temperature determined from the non-greenhouse gases, deuterium or oxygen isotopes. The gases collected are the total during the time that the aperture is open. When comparing with past methods, modern instruments may be considered instantaneous. Ice core data greatly reduces the true variability by what is known as a variance reduction ratio. They produce extremely long term averages. Furthermore, Vostok sampling, for example, has an interval of about 1,400 years. If the firn ice closes in 40 years, the probability of including an event like the modern record from Mauna Loa is about 3%. No amount of signal processing can fix this problem. What can be said about the past records of temperature and GHGs is that the answer lies somewhere between (1) a 97% confidence that it would have been missed altogether for short firn closure times, and (2) the magnitude of the ancient gases is reduced to, say, about 3% of the average modern level for long closure times, that is, on the order of a few millennia or less. In summary, the Vostok record would have missed a short event like the MLO 50-year rise in CO2, or the temperature rise since the Little Ice Age, because it skipped the event altogether or because the event was lost in the long time required for the firn to close. The statements that the modern record is unprecedented for either temperature or CO2 are invalid. The conclusion that CO2 is the cause cannot be validated based on these considerations, and in fact is invalid in a climate model that would include the following effects that IPCC and the peer-reviewed climatologists err to omit: (1) the on-going natural warming processes, (2) the outgassing of GHGs under Henry's Law, (3) the saturation effect of GHG absorption under the Beer-Lambert Law, and (4) the powerful negative cloud albedo feedback that stabilizes Earth's climate in the warm state. The flat-Earther is myopic -- his horizon is fore-shortened. He doesn't see that the ships in the distance go down by the waterline. We each need to see that the proxie records, whether from tree rings or ice cores, are down by the waterline. Anthropogenic Global Warming is analogous to the flat Earth. It is the flat Earth climate.