IPCC Third Assessment Report, 2001 Hockey stick graph

ipcc wg1 co-chair sir john t. houghton showing ipcc fig. 2.20 hockey stick graph @ climate conference in 2005

the working group 1 (wg1) part of ipcc third assessment report (tar) included subsection on multi-proxy synthesis of recent temperature change. noted 5 earlier large-scale palaeoclimate reconstructions, discussed mann, bradley & hughes 1998 reconstruction going 1400 ad , extension 1000 ad in mann, bradley & hughes 1999 (mbh99), while emphasising substantial uncertainties in earlier period. mbh99 conclusion 1990s have been warmest decade, , 1998 warmest year, of past millennium in northern hemisphere, defined 66-90% chance , supported reconstructions crowley & lowery 2000 , jones et al. 1998 using different data , methods. pollack, huang & shen 1998 reconstruction covering past 500 years gave independent support conclusion, compared against independent (extra-tropical, warm-season) tree-ring density nh temperature reconstruction of briffa 2000.

its figure 2.21 showed smoothed curves mbh99, jones et al. , briffa reconstructions, modern thermometer data red line , grey shaded 95% confidence range mbh99. above it, figure 2.20 adapted mbh99. figure 5 in wg1 technical summary b (as shown right) repeated figure without linear trend line declining ad 1000 1850.

this iconic graph adapted mbh99 featured prominently in wg1 summary policymakers under graph of instrumental temperature record past 140 years. text stated that, in northern hemisphere, 1990s warmest decade , 1998 warmest year in past 1,000 years. versions of these graphs featured less prominently in short synthesis report summary policymakers, included sentence stating increase in surface temperature on 20th century northern hemisphere have been greater other century in last thousand years , , synthesis report - questions.

the working group 1 scientific basis report agreed unanimously member government representatives in january 2001 @ meeting held in shanghai, china. large poster of ipcc illustration based on mbh99 graph formed backdrop when sir john t. houghton, co-chair of working group, presented report in announcement shown on television, leading wide publicity.