Science a GoGo's Home Page Forums General Discussion Climate Change Forum Updating Temperature Proxies

The great majority of paleoclimatology is tied to the instrumental record as best as can be done, although some use nearby stations, some use climatological data, etc.--the uncomfortable truth is that no matter how hard one blogs, you cannot make long, well-calibrated instrumental records appear at the sites where you decide to collect an ice core or lake core or
tree ring, and the long instrumental records are almost never collected in places suitable for ice-coring or lake-coring or tree-ring coring, so some long-distance or otherwise relations must be sought. Really, a textbook on the subject would be a good place to start (check Paleoclimatology in the college library), or even better, see the free, online, authoritative report from the National Academies at
http://books.nap.edu/catalog.php?record_id=11676
McIntyre is obviously an interested and dedicated individual, but does not sit in the mainstream of research on this topic, has not done too much refereed original research on it(primarily but not exclusively blogging), and is often (rightly or not) associated with one end of the political spectrum. If you are getting much information from such a source before checking
with, say, the National Academies, you are well off course for a
dispassionate consideration of the issues.

The results reported in this paper are partially in accordance with other studies that support the hypothesis of a moisture related signal in bristlecone pine. Wright and Mooney (1965) concluded that bristlecone pine responds to a precipitation gradient rather than to cool alpine temperatures. Similar results were reported from a three year ecophysiological study of bristlecone pine by Fritts (1969). Such findings are not unexpected since the White Mountains are xeric with annual precipitation not exceeding 41.5 cm. Graybill and Idso (1993) and Graybill and Funkhouser (1999) compared tree-ring widths from the western United States, including one of the sites investigated in this study (Patriarch Grove), and found similar results: a low correlation with temperature that prevents use for temperature reconstruction, a negative correlation with the previous year’s temperature, and a highly significant tree growth response to spring precipitation. Bunn et al. (2003) and Tang et al. (1999) implicated soil moisture sensitivity especially in the strip-bark trees.

Guys - thanks for enlightening me. My mental model had always been that temperatures HAVE been varying through time. Hence the mideaevel warm period and the mini ice age.

Not that one cannot compare proxies to instrumental records, but that there often is a longer distance between them than one would want, so a bit more finesse is required than simply running a regression off the nearest site.

The other issue you raise is now discussed as the "divergence problem". It is entirely a tree-ring issue so far as I know (no problem with borehole temperatures, lake biota, or any number of other indicators), and shows up as some ring-width histories failing to track the size of the most-recent warming even though they tracked the earlier-century warming well. There are many hypotheses; some of them would have no implications for temperature of Medieval Warmth, say (introduced pests reducing growth recently, other air pollutants such as tropospheric ozone reducing growth recently); whereas other hypotheses would affect the amplitude of medieval warmth (too much warmth causing drying so that tree switches from primarily temperature to primarily moisture influence could have happened in Medieval times as well). There is a discussion in the NRC report.

Notice that the fluctuations in the past have been used in model testing, but have not been used in model tuning, nor do they have much to do with attribution of prediction of climate change. If it should happen to turn out that the past fluctuations were a bit bigger than we suspect, this in no way affects attribution of recent warming to CO2--we have satellites now showing that the sun is not changing, cosmic-ray monitors showing that they
are not changing, ocean-temperature records showing that heat is going into the ocean not coming out, and other things that allow attribution now with high confidence. The efforts to use the divergence problem to argue that the Medieval warmth was warmer than previously reconstructed are typically used politically to suggest that the current warmth is natural. That is high-level nonsense, as the Medieval warmth is simply not used as part of
the attribution effort. What might come out of discovery of a warmer Medieval warmth is evidence that the long-term feedbacks are stronger than we suspected--the revisionism addresses the temperature change, not the causes of the temperature change, so a larger change from unmodified causes means a more-sensitive climate system. Causes were different then than now, but the causes load on many of the same feedbacks, so anything done to
increase our estimates of past variability should also cause concern about the future, because we will be loading on those feedbacks too.

Virtually always, the arguments about past variability are used, when they enter the political arena, in an attempt to reduce concerns about global warming. The science is exactly reversed; the more variable the past, the more worry for the future. (And yes, with a highly variable past, you can hope for an exact cancellation of human effects, but you can also fear a great amplification. There is absolutely no reason to believe that nature will somehow time itself to exactly offset us, and a more-variable hence higher-feedback past would indicate bigger future changes.)

Virtually always, the arguments about past variability are used, when they enter the political arena, in an attempt to reduce concerns about global warming. The science is exactly reversed; the more variable the past, the more worry for the future. (And yes, with a highly variable past, you can hope for an exact cancellation of human effects, but you can also fear a great amplification. There is absolutely no reason to believe that nature will somehow time itself to exactly offset us, and a more-variable hence higher-feedback past would indicate bigger future changes.)

right now the ranges don't show us being cancelled out anytime soon. Right now, real-world observations and not wishful thinking generally show that most scenarios have been underestimated, with much less overestimated

One last thing: we have a refereed scientific literature for a reason. Any issue that you see raised about climate change that has not been published in a mainstream refereed journal, you
should dismiss until the author does so. This is a necessary but not sufficient condition - incorrect things make their way into the refereed literature as well But it's at least a first
cut at deciding what's worth spending your time on. Anyone who won't subject their ideas to formal peer review...well, let the buyer beware. I've done this in a good number of forums, and have been overloaded with blogs from either side of the "debate" and we really aren't going to get far.--Chris