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56:, many tree rings from such sites do not display a corresponding change in their maximum latewood density. In some studies this issue has also been found with tree ring width. A temperature trend extracted from tree rings alone would not show any substantial warming since the 1950s. The temperature graphs calculated in these two ways thus "diverge" from one another, which is the origin of the term.
122:, hypothesizes that "beyond a certain threshold level of temperature the trees may become more stressed physiologically, especially if moisture availability does not increase at the same time." Signs suggestive of such stress are visible from space, where satellite pictures show "evidence of browning in some northern vegetation despite recent warming."
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for the period 1600–1950. Before around AD 1600, the uncertainty of temperature reconstructions rises due to the relative paucity of data sets and their limited geographic distribution. As of 2006, these uncertainties were considered too great to allow conclusion on whether the tree ring record
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in some fashion. The divergence might represent changes to other climatic variables to which tree rings are sensitive, such as delayed snowmelt and changes in seasonality. Growth rates could depend more on annual maximum or minimum temperatures, especially in temperature limited growth regions (i.e.
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Twenty-year smoothed plots of averaged ring-width (dashed) and tree-ring density (thick line), averaged across all sites, and shown as standardized anomalies from a common base (1881–1940), and compared with equivalent-area averages of mean April–September temperature anomalies (thin solid line).
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diverges from other proxies during this period. In more recent studies evidence suggested that the divergence is caused by human activities, and so confined to the recent past, but use of affected proxies can lead to overestimation of past temperatures, understating the current warming trend.
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The explanation for the divergence problem is still unclear, but is likely to represent the impact of some other climatic variable that is important to modern northern hemisphere forests but not significant before the 1950s.
76:'s February 1998 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.
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The deviation of some tree ring proxy measurements from the instrumental record since the 1950s raises the question of the reliability of tree ring proxies in the period before the
88:. The wide geographic and temporal distribution of well-preserved trees, the solid physical, chemical, and biological basis for their use, and their annual discrimination make
37:, the study of past climate through observations of old trees, primarily the properties of their annual growth rings. It is the disagreement between
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The problem of changing response of some tree ring proxies to recent climate changes was first identified through research in Alaska conducted by
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Briffa, Keith R.; Schweingruber, F. H.; Jones, Phil D.; Osborn, Tim J.; Shiyatov, S. G.; Vaganov, E. A. (12 February 1998),
182:; Schweingruber, F.H.; Jones, P.D.; Osborn, T.J.; Harris, I.C.; Shiyatov, S.G.; Vaganov, E.A.; Grudd, H. (29 January 1998).
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particularly important in pre-instrumental climate reconstructions. Tree ring proxies are essentially consistent with other
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In 2012, Brienen et al. proposed that the divergence problem was largely an artifact of sampling large living trees.
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45:) and the temperatures reconstructed from latewood densities or, in some cases, from the widths of tree rings in
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230:"On the 'Divergence Problem' in Northern Forests: A review of the tree-ring evidence and possible causes"
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fertilization from tree ring studies: The potential role of sampling biases"
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D'Arrigo, Rosanne; Wilson, Rob; Liepert, Beate; Cherubini, Paolo (2008).
184:"Trees tell of past climates: but are they speaking less clearly today?"
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Other possible explanations include that the response to recent rapid
485:"Climategate, global warming, and the tree rings divergence problem"
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high latitudes and altitudes). Another possible explanation is
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Climatic
Research Unit documents#Climate reconstruction graph
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Surface temperature reconstructions for the last 2,000 years
334:"Is a Warmer Climate Wilting the Forests of the North?"
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While the thermometer records indicate a substantial
462:. Washington, D.C.: National Academies Press. 2006.
553:Curiosity Rises With Trees' Strange Growth Spurt
285:Jacoby, Gordon C.; D'Arrigo, Rosanne D. (1995).
504:Brienen R.J.W.; Gloor E.; Zuidema P.A. (2012).
483:Velasquez-Manoff, Moises (December 14, 2009).
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54:late 20th century warming trend
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490:The Christian Science Monitor
358:10.1126/science.267.5204.1595
514:Global Biogeochemical Cycles
291:Global Biogeochemical Cycles
188:Phil. Trans. R. Soc. Lond. B
237:Global and Planetary Change
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506:"Detecting evidence for CO
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39:instrumental temperatures
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332:Taubes, Gary (1995).
101:Possible explanations
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535:10.1029/2011GB004143
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129:might be delayed or
47:far northern forests
526:2012GBioC..26B1025B
424:1998Natur.391..678B
350:1995Sci...267.1595T
303:1995GBioC...9..227J
249:2008GPC....60..289D
138:due to atmospheric
116:Columbia University
94:proxy measurements
31:divergence problem
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469:978-0-309-10225-4
311:10.1029/95GB00321
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43:thermometers
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25:et al. 1998.
578:Dendrology
567:Categories
520:: GB1025.
166:References
80:Importance
366:0036-8075
319:1944-9224
131:nonlinear
60:Discovery
390:39083329
382:17808119
149:See also
140:aerosols
522:Bibcode
440:4361534
420:Bibcode
374:2886731
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209:1692171
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21:From
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