denying 2000 years of the medieval warm period, little ice age on every continent here we go again. for five or so years believers didn’t really mention the medieval warm period. too bruised by the embarrassment of hockey stick zombie failures. but it’s an inconvenient era they have to rub out because none of the expert models can explain what caused it, and it’s hard to panic about same temperatures that edward the confessor survived with oxen and carts. and it’s hard to call the modern warmth “man-made” if nature created something just like it 1,000 years ago. by michael collett, abc, environmental copy and paste promoter climate scientists writing in the journal nature have found there is no evidence for “globally coherent warm and cold periods” over the past 2,000 years prior to industrialisation. that’s significant, because climate change deniers have sometimes pointed to epochs like the so-called “little ice age” or “medieval warm period” to argue that the current global warming is one among multiple similar global climate events. but what the research actually shows is that other “peak warming and cooling events” over the past two millennia appear to have been localised, whereas the human-caused global warming observed over the past 150 years is unparalleled in its global scale (not to mention its absolute temperatures). who’s denying a million raw data points? this new global temperature reconstruction by the pages consortium miraculously agrees with the models yet disagrees with hundreds of stalagmites, corals, ice cores, trees, lake sediments, mud from the ocean floor, pollen dust and 6,000 boreholes. it disagrees with the history of peoples like the vikings. it disagrees with plants that grew and with trees that survived “above the snowline” that shouldn’t. this map shows just some temperature estimates from all around the world during medieval times relative to today. many of these papers come from craig idso at co2science.org who maintains the medieval warm period project. back in 2009 when i did this map for the skeptics handbook ii it was a first. even then, there were already 442 separate research institutes from 41 countries which had published papers showing the mwp.* also thanks to luning and vahrenholt, and the team at notrickszone. the latest paper is trying to claim that all these temperatures were not recorded at the same time and that it wasn’t global. but when proxies are combined it’s obvious it was. even in our modern warm period, there are still warm and cold records being set at the same time. medieval times were no different. it’s only by collating and combining many proxies that we can see “the average”. 18 proxies tell us the world was the same or warmer 1,000 years ago craig loehle in 2008 used 18 non-tree-ring proxies which included greenland borehole data, conroy lake pollen, isotopes from chesapeake bay, sargasso sea, caribbean sea, results from caves in south africa, the swiss alps, sea surface reconstructions from norway, the northern pacific and the south atlantic and other proxies too. temperatures were higher 1000 years ago, and cooler 300 years ago. we started warming long before cars and powerstations were invented. there’s little correlation with co2 levels. here’s what 120 proxies from the northern hemisphere tell us ljungqvist et al combined 120 proxies of all different kinds and found this pattern for the last 12 centuries across the northern hemisphere. then there’s christiansen et al 2012 who followed 32 proxies from the northern hemisphere back to the year 0 ad. here’s the medieval warm period in china here’s the medieval warm period in antarctica, and the little ice age: just in case you thought there wasn’t enough from the southern hemisphere. rosenthal et al 2013 put out quite the zinger of a paper. they’ve reconstructed the temperature of the water flowing out of the pacific to the indian ocean over the last 10,000 years and as deep as 900m. the indonesian throughflow is pretty significant in global ocean currents. clearly that water was warmer 1000 years ago than it was circa 1970. it was even warmer again in the holocene. 3000 hot and cold years in a south african cave south african cave last 3000 years source: holmgren 2001. see also here and here in african reconstructions. the southern ocean 7000 year record also shows long term cooling as well as the roman warm period. then there’s 10,000 mostly hotter years in greenland no paleoclimate discussion is complete without gisp: 6,000 boreholes show it was global just some of the places these boreholes have been dug. they stick a thermometer down a hole, and all over the world there is a pattern that repeats as temperature changes on the surface travel gradually down through the rocks. sure, the resolution is bare bones. the data is “smoothed”. we can’t use boreholes to know if things were warmer than today and we can’t tell how long ago that big last surge in warmth was, but where boreholes come into their own is in showing us just how global that last big warm spell was. below is the latest iteration of a graph that went through a savage evolution from 1997 – 2008. what stayed constant was that boreholes always showed a medieval warm period and a little ice age, that is, except for the time huang et al “lost” nearly 20,000 years of data. in the graph above, if the assumption about the speed of heat flow is shifted to line up the coolest point with other proxies in 1680 and the warmest point to somewhere around 1000 – 1200 the amplitude would increase (see the jaw dropping 1997 original paper which claimed it was much warmer in medieval times). these papers are by no means the only important ones. there are so many others… so go tell the world — everywhere we look the world was hotter and colder in the last 1000 years, the last 10,000 years and the last billion. h/t george, david b, original steve, peter fitzroy. climate data has long verified, that m.w.p. and l.i.a. were worldwide, when a co2 dearth, all over the earth, to the warming and cooling applied. — ruairi background information: references pages 2k consortium. consistent multidecadal variability in global temperature reconstructions and simulations over the common era. nature, 2019 doi: 10.1038/s41561-019-0400-0 christiansen, b. and ljungqvist f. c. (2012). the extra-tropical northern hemisphere temperature in the last two millennia: reconstructions of low-frequency variability. climate of the past, 8(2):765–786, 2012. [abstract] [pdf] [nasa copy] [discussion on ca noted a lack of complete archives and code] holmgren, k., tyson, p.d., moberg, a. and svanered, o. 2001. a preliminary 3000-year regional temperature reconstruction for south africa. south african journal of science 97: 49-51. loehle, c. 2007. a 2000 year global temperature reconstruction based on non-treering proxy data. energy & environment 18:1049-1058) and the subsequent correction with better confidence intervals loehle, c. and hu mcculloch. 2008. correction to: a 2000 year global temperature reconstruction based on non-treering proxy data. energy & environment 19:93-100 [cached copy here] ljungqvist, f. c., krusic, p. j., brattström, g., and sundqvist, h. s (2012).: northern hemisphere temperature patterns in the last 12 centuries, clim. past, 8, 227-249, doi:10.5194/cp-8-227-2012, 2012. [abstract] [pdf] or try this [pdf] [co2science discussion] lüning, s., m. gałka, f. vahrenholt (2019): the medieval climate anomaly in antarctica. palaeogeogr., palaeoclimatol., palaeoecol., doi:10.1016/j.palaeo.2019.109251 sources: loehle 2007, haung and pollack 1997, see co2science.org for all the other peer reviewed studies to go with every orange dot on the map. mcintyre & mckitrick 2003 and 2005, and update, mann et al 1998, briffa 2006, and monckton “what hockey stick” (science and public policy institute paper) quansheng ge et al, characteristics of temperature change in china over the last 2000 years and spatial patterns of dryness/wetness during cold and warm periods, advances in atmospheric sciences (2017). doi: 10.1007/s00376-017-6238-8 yair rosenthal1,*, braddock k. linsley2, delia w. oppo3 (2013) pacific ocean heat content during the past 10,000 years, science 1 november,vol. 342 no. 6158 pp. 617-621 doi: 10.1126/science.1240837 [sciencemag.org ] ______________________ * the world map was created by looking at studies listed on co2science.org. craig idso divided up studies into three different levels. level 1 is the most useful, because they are able to tell us, not just whether the world is warming or not, but but also give a number. the level 2 studies just tell us whether things were warmer or cooler at that location, and with a specific timeframe. the level 3 studies are useful for pinpointing the time frame of the warming. all three levels are represented by orange dots. the numbers come from the level 1 studies. i did not put all the positive ones i could find because there were so many, but i included all the negatives i came across. there were 57 studies of a level 1 category (bound to be more now). there was clearly a warm period and it was clearly global.
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