Paleoclimatology dates back to the 19th century, and the concept of examining varves in lake beds and tree rings to track local climatic changes was suggested in the s. This was the basis of a "schematic diagram" featured in the IPCC First Assessment Report of beside cautions that the medieval warming might not have been global.
History of climate change science and Description of the Medieval Warm Period and Little Ice Age in IPCC reports Paleoclimatology influenced the 19th century physicists John Tyndall and Svante Arrhenius who found the greenhouse gas effect of carbon dioxide CO2 in the atmosphere to explain how past ice ages had ended.
Bradley showed that annual varves in lake beds showed climate cycles, and A. Douglass found that tree rings could track past climatic changes but these were thought to only show random variations in the local region. It was only in the s that accurate use of tree rings as climate proxies for reconstructions was pioneered by Harold C.
In Hubert Lamba pioneer of historical climatologygeneralised from temperature records of central England by using historical, botanical and archeological evidence to popularise the idea of a Medieval Warm Period from around tofollowed by a cold epoch culminating between and They used "a short-cut method" based on their earlier paper which showed that 9 instrumental stations could adequately represent an extensive gridded instrumental series, and reconstructed temperatures from to on the basis of their compilation of 20 time-series.
These records were largely instrumental but also included some proxy records including two tree-ring series. Their method used nested multiple regression to allow for records covering different periods, and produced measures of uncertainty.
The reconstruction showed a cool period extending beyond the Maunder Minimumand warmer temperatures in the 20th century.
This was the first based entirely on non-instrumental records, and used tree rings. From this, they concluded that recent warming was anomalous over the year period, and went as far as speculating that these results supported the hypothesis that recent warming had human causes.
The report discussed the difficulties with proxy data, "mainly pollen remains, lake varves and ocean sediments, insect and animal remains, glacier termini" but considered tree ring data was "not yet sufficiently easy to assess nor sufficiently integrated with indications from other data to be used in this report.
BradleyMalcolm K. Climate proxy temperature data was needed at seasonal or annual resolution covering a wide geographical area to provide a framework for testing the part climate forcings had played in past variations, look for cycles in climate, and find if debated climatic events such as the Little Ice Age and Medieval Warm Period were global.
Reconstructions were to be made of key climate systems, starting with three climatically sensitive regions: Areas where more data was needed were to be identified, and there was a need for improved data exchange with computer-based archiving and translation to give researchers access to worldwide paleoclimate information.
These included a study of 1, years of tree ring data from Tasmania which, like similar studies, did not allow for possible overestimate of warming due to increased CO2 levels having a fertilisation effect on tree growth. It noted the suggestion of Bradley et al.
Bradley and Phil Jones composited historical records, tree-rings and ice cores for the Northern Hemisphere from up to the s to produce a decadal reconstruction. It concluded that the "Little Ice Age" period was complex, with evidence suggesting the influence of volcanic eruptions.
It showed that temperatures since the s were higher than earlier in the year period, an indication of other factors which could most probably be attributed to human caused changes increasing levels of greenhouse gases. In this method, also known as "Composite Plus Scale", selected climate proxy records were standardized before being averaged compositedand then centred and scaled to provide a quantitative estimate of the target temperature series for the climate of the region or hemisphere over time.
This method was implemented in various ways, including different selection processes for the proxy records, and averaging could be unweighted, or could be weighted in relation to an assessment of reliability or of area represented.
There were also different ways of finding the scaling coefficient used to scale the proxy records to the instrumental temperature record. Eddy had earlier tried to relate the rarity of sunspots during the Maunder Minimum to Lamb's estimates of past climate, but had insufficient information to produce a quantitative assessment.
A reconstruction of Arctic temperatures over four centuries by Overpeck et al. It stated that in this record, warming since the late 19th century was unprecedented.
The section proposed that "The data from the last years are the most useful for determining the scales of natural climate variability". Recent studies including the reconstruction by Hughes and Diaz questioned how widespread the Medieval Warm Period had been at any one time, thus it was not possible "to conclude that global temperatures in the Medieval Warm Period were comparable to the warm decades of the late 20th century.
In at least some areas, the recent period appears to be warmer than has been the case for a thousand or more years". Tree ring specialist Keith Briffa 's February study showed that this problem was more widespread at high northern latitudes, and warned that it had to be taken into account to avoid overestimating past temperatures.The Hockey Stick: The Most Controversial Chart in Science, Explained Climate deniers threw all their might at disproving the famous climate change graph.
Here's why they failed. Hockey Stick End Table Plans. Hockey stick controversy - WikipediaIn the hockey stick controversy, the data and methods used in reconstructions of the temperature record of .
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Since the hockey stick paper in , there have been a number of proxy studies analysing a variety of different sources including corals, stalagmites, tree rings, boreholes and ice cores.
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