Query: Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.

Relevant passages:
Michael E. Mann <=SEP=> Michael E. Mann ( born 1965 ) is an American climatologist and geophysicist , currently director of the Earth System Science Center at Pennsylvania State University , who has contributed to the scientific understanding of historic climate change based on the temperature record of the past thousand years . He has pioneered techniques to find patterns in past climate change , and to isolate climate signals from noisy data .   As lead author of a paper produced in 1998 with co-authors Raymond S. Bradley and Malcolm K. Hughes , Mann used advanced statistical techniques to find regional variations in a hemispherical climate reconstruction covering the past 600 years . In 1999 the same team used these techniques to produce a reconstruction over the past 1,000 years ( MBH99 ) which was dubbed the `` hockey stick graph '' because of its shape . He was one of eight lead authors of the `` Observed Climate Variability and Change '' chapter of the Intergovernmental Panel on Climate Change ( IPCC ) Third Scientific Assessment Report published in 2001 . A graph based on the MBH99 paper was highlighted in several parts of the report , and was given wide publicity . The IPCC acknowledged that his work , along with that of the many other lead authors and review editors , contributed to the award of the 2007 Nobel Peace Prize , which was won jointly by the IPCC and Al Gore .   Mann was organizing committee chair for the National Academy of Sciences Frontiers of Science in 2003 and has received a number of honors and awards including selection by Scientific American as one of the fifty leading visionaries in science and technology in 2002 . In 2012 he was inducted as a Fellow of the American Geophysical Union and was awarded the Hans Oeschger Medal of the European Geosciences Union . In 2013 he was elected a Fellow of the American Meteorological Society , and awarded the status of distinguished professor in Penn State 's College of Earth and Mineral Sciences .   Mann is author of more than 200 peer-reviewed and edited publications . He has also published three books : Dire Predictions : Understanding Global Warming ( 2008 ) , The Hockey Stick and the Climate Wars : Dispatches from the Front Lines ( 2012 ) , and , together with co-author Tom Toles , The Madhouse Effect : How Climate Change Denial Is Threatening Our Planet , Destroying Our Politics , and Driving Us Crazy ( 2016 ) . In 2012 , the European Geosciences Union described his publication record as `` outstanding for a scientist of his relatively young age '' . Mann is also a co-founder and contributor to the climatology blog RealClimate .

Divergence problem <=SEP=> The divergence problem is an anomaly from the field of dendroclimatology , the study of past climate through observations of old trees , primarily the properties of their annual growth rings . It is the disagreement between the temperatures measured by the thermometers ( instrumental temperatures ) and the temperatures reconstructed from the latewood densities or , in some cases , widths of tree rings in the far northern forests .   While the thermometer records indicate a substantial late 20th century warming trend , 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 .

Temperature record of the past 1000 years <=SEP=> For information on the description of the Medieval Warm Period and Little Ice Age in various IPCC reports see MWP and LIA in IPCC reportsThe temperature record of the past 1,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 150 years at a global scale . Large-scale reconstructions covering part or all of the 1st millennium and 2nd millennium have shown that recent temperatures are exceptional : the Intergovernmental Panel on Climate Change Fourth Assessment Report of 2007 concluded that `` Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely '' the highest in at least the past 1,300 years . '' The curve shown in graphs of these reconstructions is widely known as the hockey stick graph because of the sharp increase in temperatures during the last century . As of 2010 this broad pattern was supported by more than two dozen reconstructions , using various statistical methods and combinations of proxy records , with variations in how flat the pre-20th-century `` shaft '' appears . Sparseness of proxy records results in considerable uncertainty for earlier periods .   Individual proxy records , such as tree ring widths and densities used in dendroclimatology , are calibrated against the instrumental record for the period of overlap . Networks of such records are used to reconstruct past temperatures for regions : tree ring proxies have been used to reconstruct Northern Hemisphere extratropical temperatures ( within the tropics trees do not form rings ) but are confined to land areas and are scarce in the Southern Hemisphere which is largely ocean . Wider coverage is provided by multiproxy reconstructions , incorporating proxies such as lake sediments , ice cores and corals which are found in different regions , and using statistical methods to relate these sparser proxies to the greater numbers of tree ring records . The `` Composite Plus Scaling '' ( CPS ) method is widely used for large-scale multiproxy reconstructions of hemispheric or global average temperatures ; this is complemented by Climate Field Reconstruction ( CFR ) methods which show how climate patterns have developed over large spatial areas , making the reconstruction useful for investigating natural variability and long-term oscillations as well as for comparisons with patterns produced by climate models .   During the 1,900 years before the 20th century , it is likely that the next warmest period was from 950 to 1100 , with peaks at different times in different regions . This has been called the Medieval Warm Period , and some evidence suggests widespread cooler conditions during a period around the 17th century known as the Little Ice Age . In the hockey stick controversy , contrarians have asserted that the Medieval Warm Period was warmer than at present , and have disputed the data and methods of climate reconstructions .