Y lo del óptimo medieval es mentira, ya me dirás donde lo ves más alto que el presente en esta recopilación de reconstrucciones...pero en fin...una mentira mil veces repetida...
Es muy dificil decir algo con certeza absoluta, porque aunque tengamos un millon de observaciones que lo confirman, a lo mejor la observacion un millon y uno echa por tierra nuestra teoria.
Se ha dicho que el optimo medieval era un fenomeno local. Puede que sea asi, lo malo es que con tantos sitios que lo muestran hay que buscar una zona global un poco retorcida:
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- Giraudi: Late Holocene glacial and periglacial evolution in the upper Orco Valley, in: Quaternary Research, 71, 2009.
- Mangini et al.: Reconstruction of temperature in the Central Alps during the past 2000 yr froma y180 stalagmite record, in: Earth and Planetary Science Letters 235, 2005.
- Büntgen et al.: Summer Temperature Variations in the European Alps, AD 755-2004, in: Journal of Climate, Volume 19, 2006.
- Dahl-Jensen et al.: Past Temperature Directly from the Greenland Ice Sheet, in: Science, Vol. 282, 9. October 1998.
- Vinther et al.: Climatic signals in multiple highly resolved stable isotope records from Greenland, in: Quaternary Science Reviews, Volume 29, Issues 3-4, February 2010.
- Paul et al.: Diatom-inferred climatic and environmental changes over the last ~9000 years from a low Arctic (Nunavut, Canada) tundra lake, in: Palaoegeography, Palaeoclimatology, Palaeoecology, Volume 291, Issues 3-4, 15. May 2010.
- Ran et al.: Diatom-based reconstruction of palaeoceanographic changes on the North Icelandic shelf during the last millennium, in: Palaoegeography, Palaeoclimatology, Palaeoecology, Article in Press, Corrected Proof.
- Tandong et al.: Temperature and methane records over the last 2ka in Dasuopu ice core, in: Science in China, Vol. 45, No. 12, Dezember 2002.
- Demezhko und Golovanova: Climatic changes in the Urals over the past millennium - an alnalysis of geothermal and meteorological data, in: Climate Past, 3, 2007.
- Cook et al.: Evidence for a 'Medieval Warm Period' in a 1,100 year tree-ring reconstruction of past austral summer temperatures in New Zealand, in: Geophysical Research Letters, Vol. 29, No. 14, 2002.
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Ljungqvist:
"Temperature proxy records covering the last two millennia: a tabular and visual overview"
Here, the first systematic survey is presented, with graphic representations of most quantitative temperature proxy data records covering the last two millennia that have been published in the peer-reviewed literature. In total, 71 series are presented together with basic essential information on each record. ... Both the Medieval Warm Period, the Little Ice Age and the 20th century warming are clearly visible in most records, whereas the Roman Warm Period and the Dark Age Cold Period are less clearly discernible.
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/ljungqvist2009/ljungqvist2009recons.txt Temperature Proxy Records Covering the Last Two Millennia