2010 onwards Hockey stick graph

a 2,000 year extratropical northern hemisphere reconstruction ljungqvist published geografiska annaler in september 2010 drew on additional proxy evidence show both roman warm period , medieval warm period decadal mean temperatures reaching or exceeding reference 1961–1990 mean temperature level. instrumental records of period 1990–2010 possibly above temperature in reconstruction period, though did not appear in proxy records. concluded reconstruction agrees reconstructions moberg et al. (2005) , mann et al. (2008) regard amplitude of variability timing of warm , cold periods, except period c. ad 300–800, despite significant differences in both data coverage , methodology.

a 2010 opinion piece david frank, jan esper, eduardo zorita , rob wilson (frank et al. 2010) noted on 2 dozen large-scale climate reconstructions had been published, showing broad consensus there had been exceptional 20th century warming after earlier climatic phases, notably medieval warm period , little ice age. there still issues of large-scale natural variability resolved, lowest frequency variations, , called further research improve expert assessment of proxies , develop reconstruction methods explicitly allowing structural uncertainties in process.

as several studies had noted, regression-based reconstruction methods tended underestimate low-frequency variability. bo christiansen designed new method (loc) overcome problem, , ljungqvist used loc produce 1,000 year reconstruction published in 2011. showed more low frequency variability , colder little ice age previous studies. extended loc reconstruction using selected proxies had documented relation temperature , passed screening procedure. 2,000 year reconstruction, published in 2012, again showed more variability earlier reconstructions. found homogenous little ice age 1580–1720 showing colder conditions in areas, , defined possibly less homogenous medieval warm period peak around 950–1050, reaching or exceeding mid 20th century temperatures indicated previous studies including mann et al. 2008 , 2009.

ljungqvist et al. 2012 used larger network of proxies previous studies, including use low-resolution proxy data few 2 data points per century, produce reconstruction showing centennial patterns of temperature variability in space , time northern hemisphere land areas on last 1,200 years. @ broad scale, found widespread warmth 9th 11th centuries approximating 20th century mean, dominant cooling 16th 18th centuries. greatest warming occurred 19th 20th centuries, , noted instrumental records of recent decades warmer 20th century mean. spatial reconstruction showed similarities mann et al. 2009 climate field reconstruction, though different resolution meant these not directly comparable. results robust, when significant numbers of proxies removed.

marcott et al. 2013 used seafloor , lake bed sediment proxies, independent of used in earlier studies, reconstruct global temperatures on past 11,300 years, covering entire holocene, , showing on last 1,000 years confirmation of original mbh99 hockey stick graph. temperatures had risen last ice age reach level lasted 10,000 5,000 years ago, in line milankovitch cycles had begun slow decline, interrupted small rise during medieval warm period, little ice age. decline had been interrupted uniquely rapid rise in 20th century temperatures warmest @ least 4,000 years, within range of uncertainties of highest temperatures in whole period, , on current estimates exceed temperatures 2100.