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Global Temperature - Not so anomalous now

Craig Loehle

Historical data provide a baseline for judging how anomalous recent temperature changes are and for assessing the degree to which organisms are likely to be adversely affected by current or future warming. Climate histories are commonly reconstructed from a variety of sources, including ice cores, tree rings, and sediment. Tree-ring data, being the most abundant for recent centuries, tend to dominate reconstructions. There are reasons to believe that tree ring data may not properly capture long-term climate changes..... In this study, eighteen 2000-year-long series were obtained that were not based on tree ring data. Loehle (2007) obtained data for long series that had been previously calibrated and converted to temperature by their respective authors. Essentially no tree ring data were used. After an extensive search, all data were used that had at least 20 dates over the 2000-year period.....


The Medieval Warming Period (MWP) was significantly warmer than the bimillennial average during most of the period 820 - 1040 AD. The Little Ice Age was significantly cooler than the average during most of 1440 - 1740 AD. The warmest tridecade of the MWP was warmer than the most recent tridecade, but not significantly so.


More discussion here

See below for the global distribution of the proxies included in the study.



I've always had a problem with the use of any proxies in the creation of predictive models, especially tree ring data.

From what I have seen, the predictions made by climate change models can be affected by very small changes in parameters or factors. Yet if one looks at tree rings they are quite variable and also quite narrow. Thus making accurate measurements of the exact width (as opposed to vague generalisations) must be quite hard.

Similarly temperature is but one of the natural variables that can effect rate of growth. Off the top of my head I can list three (rainfall, changes in the amount of nutrients in the soil and hours of sunshine) that may also have their influence quite seperate from temperature.

Whether the scientists took cognisence of these other factors isn't apparent. But to my mind, proxies, like tree rings, can provide trend indicators at best. Speaking as an engineer, that's not the sort of info one would wish to use in predictive models of the sort of complexity climate models must contain.

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