America : Good while it lasted

[Xywalan]

Originally posted by Blog
Alot of non scientists are confused by this and think you can just take out the part that doesn't match no problem. This is not the case, If you're theory isn't valid from 1960 on. What is to say it isn't valid pre 1900? Nothing, that is why you need to find the root cause of why it is not valid from 1960 on and not just pretend like it never happened or keep adding ad hoc conditions to make it work. Its not exactly manipulating the data, its just flat bad science.

This is the MBH98 paper, essentially the source of the "trick" email. Look at page 1 where it says what kind of data they are using: tree ring, ice core, coral and many more. Thus, the tree-ring data matches the other proxies when they are available. Just because we do not understand something, it does not mean we should throw away the available evidence. The observed divergence makes tree-ring data less reliable but given the evidence of past correlation, you cannot just throw away that data. The correct approach is to add more proxies and more data.

And at the time divergence was known:

During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known, but if it is not taken into account in dendroclimatic reconstructions, past temperatures could be overestimated. Moreover, the recent reduction in the response of trees to air-temperature changes would mean that estimates of future atmospheric CO2 concentrations, based on carbon-cycle models that are uniformly sensitive to high-latitude warming, could be too low.

And essentially, this issue doesn't change the big picture because since that time scientists were working on getting reconstructions that did not use tree-ring data. Take a look at this realclimate post that discusses this paper:

abstract. Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature Reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels.

Finally, if you check the debate video that I posted before, none of these really matter. It does not matter whether we have had similar anomalies in the past or whether the temperature in the past was higher than normal. The facts are that at the moment we are vulnerable to sudden increases in temperature, climate sensitivity to CO2 is high (i.e., increasing CO2 will cause noticeable warming), atmospheric CO2 is increase by about 40%, all the increase in CO2 is due to us, and human activity dwarfs the CO2 emitted by volcanos, 100 to 1.