Origins: the first paleoclimate reconstructions Hockey stick graph

paleoclimatology influenced 19th century physicists john tyndall , svante arrhenius found greenhouse gas effect of carbon dioxide (co2) in atmosphere explain how past ice ages had ended. 1919 1923, alfred wegener did pioneering work on reconstructing climate of past eras in collaboration milutin milanković, publishing die klimate der geologischen vorzeit (“the climates of geological past”) wladimir köppen, in 1924. in 1930s guy stewart callendar compiled temperature records changes. wilmot h. bradley showed annual varves in lake beds showed climate cycles, , a. e. douglass found tree rings track past climatic changes these thought show random variations in local region. in 1960s accurate use of tree rings climate proxies reconstructions pioneered harold c. fritts.

red line: rescaled ipcc 1990 figure 7.1(c), based on lamb 1965 showing central england temperatures; compared central england temperatures 2007, shown in jones et al. 2009 (green dashed line). shown, mann, bradley & hughes 1998 40 year average used in ipcc tar 2001 (blue), , moberg et al. 2005 low frequency signal (black).

in 1965 hubert lamb, pioneer of historical climatology, generalised temperature records of central england using historical, botanical , archeological evidence popularise idea of medieval warm period around 900 1300, followed cold epoch culminating between 1550 , 1700. in 1972 became founding director of climatic research unit (cru) in university of east anglia (uea), aimed improve knowledge of climate history in both recent , far distant past, monitor current changes in global climate, identify processes causing changes @ different timescales, , review possibility of advising future trends in climate. during cold years of 1960s, lamb had anticipated natural cycles lead on thousands of years future ice age, after 1976 supported emerging view greenhouse gas emissions caused humanity cause detectable global warming a.d. 2000 .

the first quantitative reconstruction of northern hemisphere (nh) annual mean temperatures published in 1979 brian groveman , helmut landsberg. used short-cut method based on earlier paper showed 9 instrumental stations adequately represent extensive gridded instrumental series, , reconstructed temperatures 1579 1880 on basis of compilation of 20 time-series. these records largely instrumental included proxy records including 2 tree-ring series. method used nested multiple regression allow records covering different periods, , produced measures of uncertainty. reconstruction showed cool period extending beyond maunder minimum, , warmer temperatures in 20th century. after around decade elapsed before gordon jacoby , rosanne d arrigo produced next quantitative nh reconstruction, published in 1989. first based entirely on non-instrumental records, , used tree rings. reconstructed northern hemisphere annual temperatures since 1671 on basis of boreal north american tree ring data 11 distinct regions. this, concluded recent warming anomalous on 300-year period, , went far speculating these results supported hypothesis recent warming had human causes.

ipcc first assessment report, 1990, supplement, 1992

publicity on concerns of scientists implications of global warming led increasing public , political interest, , reagan administration, concerned in part political impact of scientific findings, lobbied 1988 formation of intergovernmental panel on climate change produce reports subject detailed approval government delegates. ipcc first assessment report in 1990 noted evidence holocene climatic optimum around 5,000-6,000 years ago had been warmer present (at least in summer) , in areas there had been exceptional warmth during shorter medieval warm period (which may not have been global) ad 950-1250, followed cooler period of little ice age ended in middle late nineteenth century. report discussed difficulties proxy data, pollen remains, lake varves , ocean sediments, insect , animal remains, glacier termini considered tree ring data not yet sufficiently easy assess nor sufficiently integrated indications other data used in report. schematic diagram of global temperature variations on last thousand years has been traced graph based loosely on lamb s 1965 paper, nominally representing central england, modified lamb in 1982. mike hulme describes schematic diagram lamb s sketch on of envelope , rather dodgy bit of hand-waving .

in bradley et al. 1991, working group of climatologists including raymond s. bradley, malcolm k. hughes, jean jouzel, wibjörn karlén, jonathan overpeck , tom wigley proposed project improve understanding of natural climatic variations on last 2 thousand years effect allowed when evaluating human contributions climate change. climate proxy temperature data needed @ seasonal or annual resolution covering wide geographical area provide framework testing part climate forcings had played in past variations, cycles in climate, , find if debated climatic events such little ice age , medieval warm period global. reconstructions made of key climate systems, starting 3 climatically sensitive regions: asian monsoon region, el niño–southern oscillation region , atlantic region. areas more data needed identified, , there need improved data exchange computer-based archiving , translation give researchers access worldwide paleoclimate information.

the ipcc supplementary report, 1992, reviewed progress on various proxies. these included study of 1,000 years of tree ring data tasmania which, similar studies, did not allow possible overestimate of warming due increased co2 levels having fertilisation effect on tree growth. noted suggestion of bradley et al. 1991 instrumental records in specific areas combined paleoclimate data increased detail 18th century.