Temperaturas nada extraordinarias. Ya no hay Palo de Hockey ni Mann que valga
Los mete miedos necesitaban un icono gráfico y semántico para convencernos de que el fin del mundo estaba próximo, si no dejábamos de ser malos. Y llegó Michael Mann con su “palo de hockey”, conejo sacado de la chistera con estadística bastarda, diciendo que la temperatura actual no tenía precedentes en los últimos 1.500 años.
¿Y el famoso período Cálido Medieval?
¡Un cuento!, proclamaba Mann. O en todo caso un fenómeno local circunscrito al área de Europa y Groenlandia, donde no había forma de esconderlo. Pero a nivel global, ahora hace un calor como nunca, y la culpa solo puede ser del hombre pecador.
Pues no. El Palo de Hockey era trampa y las investigaciones más modernas vuelven a rescatar el Período Cálido Medieval. Como es un asunto relativamente abstruso no se puede estar hablando de él con frecuencia. Pero es muy interesante saber si las temperaturas actuales son extraordinarias, o muy normales. Por eso aprovecho para traer una entrevista que Von Storch señala en su blog, donde le preguntan al eminente paleoclimatólogo austríaco Reinhard Böhm sobre el asunto.
Es en alemán, así que solo voy a enlazarla y a poner el hiper resumen final del propio Böhm. Y también aprovecharé para poner enlaces a los estudios recientes que citan en la entrevista (estos son en inglés).
Menschen im Gespräch: Teil II
--W.v.B.: Muy estimado Herr Dr. Böhm, me gustaría que me hiciera un breve resumen de las respuestas que nos ha dado, por favor.
Dr. Böhm: Se las daré muy breves:
-
Período Cálido Medieval, sí.
-
En algunas regiones, como en los Alpes, incluso cuantificables, y similar calor entre las temperaturas de le Edad Media y las últimas décadas del sglo XX.
-
De hemisférico a global, también, pero no tan fácil de cuantificar.
-
Físicamente todavía no está afinado del todo, pero vamos camino.
W.v.B. Ich danke für das Gespräch!
–
Enlaces:
Uno previo, ajeno a este artículo, pero probablemente la mejor recopilación de literatura científica sobre el PCM por todas partes:
Algunos citados en la entrevista de Böhm:La similitud de registros entre los Alpes, Groenlandia, y Bermuda, sugieren un gran impacto del PCM a en el Hemisferio Norte. La diferencia de temperatura con la Pequeña Edad de Hielo (1600 - 1850) es por término medio de unos 1,7ºC. Esta diferencia es significativamente mayor que la que da el informe del IPCC.
Joint analysis of GSTH and meteorological data bring us to the following conclusions. First, ground surface temperatures in the Medieval maximum during 1100–1200 were 0.4 K higher than the 20th century mean temperature (1900–1960). The Little Ice Age cooling was culminated in 1720 when surface mean temperature was 1.6 K below the 20th century mean temperature. Secondly, contemporary warming began approximately one century prior to the first instrumental measurements in the Urals. The rate of warming was +0.25 K/100 years in the 18th century, +1.15 K/100 years in the 19th and +0.75 K/100 years in the first 80 years of the 20th century. Finally, the mean rate of warming increased in the final decades of 20th century. An analysis of linear regression coefficients in running intervals of 21 and 31 years, shows that there were periods of warming with almost the same rates in the past, including the 19th century.
The identification of a MWP sensu lato in New Zealand adds an important new datum to the debate concerning its large-scale occurrence and supports Broecker’s[2001] argument that it was indeed global. The identification of a MWP sensu lato in NewZealand adds an important new datum to the debate con-cerning its large-scale occurrence and supports Broecker’s[2001] argument that it was indeed global.
Proxy data are our only source of knowledge of temperature variability in the period prior to instrumental temperature measurements. Until recently, very few quantitative palaeotemperature records extended back a millennium or more, but the number is now increasing. 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. This overview will hopefully assist future palaeoclimatic research by facilitating an orientation among available palaeotemperature records and thus reduce the risk of missing less well-known proxy series. The records show an amplitude between maximum and minimum temperatures during the past two millennia on centennial timescales ranging from c. 0.5 to 4°C and averaging c. 1.5–2°C for both high and low latitudes, although these variations are not always occurring synchronous. 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.--
Más literatura:
- Barclay, D.J., Wiles, G.C., and Calkin, P.E. 2009. Tree-ring crossdates for a first millennium AD advance of Tebenkof Glacier, southern Alaska. Quaternary Research, 71: 22–26.
- Cook, T.L., Bradley, R.S., Stoner, J.S. and Francus, P., 2009: Five thousand years of sediment transfer in a high arctic watershed recorded in annually laminated sediments from Lower Murray Lake, Ellesmere Island, Nunavut, Canada. Journal of Paleolimnology, 41: 77–94.
- Esper, J. and Frank, D.C., 2009: IPCC on heterogeneous Medieval Warm Period. Climatic Change, 94: 267–273.
- Ge, Q., Zheng, J., Fang, X., Man, Z., Zhang, X., Zhang, P., and Wang, W.-C., 2003: Winter half-year temperature reconstruction for the middle and lower reaches of the Yellow River and Yangtze River, China, during the past 2000 years. The Holocene, 13: 933–940.
- Ge, Q.S., Zheng, J.-Y., Hao, Z.-X., Shao, X.-M., Wang, W.-C., and Luterbacher, J., 2010: Temperature variation through 2000 years in China: An uncertainty analysis of reconstruction and regional difference. Geophysical Research Letters, 37: 10.1029/2009GL041281.
- Jones, P.D., Briffa, K.R., Osborn, T.J., Lough, J.M., van Ommen, T.D., Vinther, B.M., Luterbacher, J., Wahl, E.R., Zwiers, F.W., Mann, M.E., Schmidt, G.A., Ammann, C.M., Buckley, B.M., Cobb, K.M., Esper, J., Goosse, H., Graham, N., Jansen, E., Kiefer, T., Kull, C., Küttel, M., Mosley-Thompson, E., Overpeck, J.T., Riedwyl, N., Schulz, M., Tudhope, A.W., Villalba, R., Wanner, H., Wolff, E. and Xoplaki, E., 2009: High-resolution palaeoclimatology of the last millennium: A review of current status and future prospects. The Holocene, 19: 3
- Mann, M.E., Zhang, Z., Rutherford, S., Bradley, R.S., Hughes, M.K., Shindell, D., Ammann, C., Faluvegi, G., and Ni, F., 2009: Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly. Science, 326: 1256–1260.
- Moberg, A., Sonechkln, D.M., Holmgren, K., Datsenko, N.M., and Karlén, W., 2005: Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature, 433: 613–617.
- Neukom, R., Luterbacher, J., Villalba, R., Küttel, M., Frank, D., Jones, P.D., Grosjean, M., Wanner, H., Aravena, J.-C., Black, D.E., Christie, D.A., D’Arrigo, R., Lara, A., Morales, M., Soliz-Gamboa, C., Srur, A., Urrutia, R., and von Gunten, L., 2010: Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries. Climate Dynamics: in press.
- Yang, B., Braeuning, A., Johnson, K.R., and Yafeng, S., 2002: General characteristics of temperature variation in China during the last two millennia. Geophysical Research Letters, 29: 1324.
- Wanner, H., Beer, J., Bütikofer, J. Crowley, T., Cubasch, U., Flückiger, J., Goosse, H., Grosjean, M., Joos, F., Kaplan, J.O., Küttel, M., Müller, S., Pentice, C. Solomina, O., Stocker, T., Tarasov, P., Wagner, M., and Widmann, M., 2008: Mid to late Holocene climate change – an overview. Quaternary Science Reviews, 27: 1791–1828.