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Climate reconstruction
Impacts of climate extremes on tree growth: the example of the 1976 severe summer drought in Western Europe
A) Annual variation in tree-ring width and density in a Pinus sylvestris sample from the Rhone Valley in Southern Switzerland - note the narrow and low-density ring formed in 1976.
B) Summer climate conditions and growth anomalies across central and western Europe in 1976. The 1976 summer was both hot and dry (red colors), causing narrow rings at many tree sites where growth is known to be limited by precipitation amounts (P; triangles) or mixtures of thermal and hydrological limitations (M; squares).
C) 500 years of growth extremes across Europe. Years where more than 1/3 of the regional growth series (maximum of 15) showed growth extremes are labeled.
Figure extended from Babst et al. (2012). Click on picture to enlarge.

Instrumental records demonstrate a rapid warming at regional to global scales as well as large changes in the Earth’s water cycle during the past 50- 100 years. But what causes these trends and are they unusual?

Tree-ring data offer one of the few opportunities to reconstruct variations in the Earth’s climate at annual-resolution, and thereby place recent instrumental records in the context of climate system variability prior to the industrial era. Such long-term records are crucial to test climate models’ abilities to hindcast changes over the past millennium and thus improve predictions for the next centuries.

WSL researchers specialize in the collection, production and analysis of tree-ring width, maximum latewood density, and stable isotopes measurements to quantify past climate change across the globe. 

Selected publications

Neukom R, Gergis J, Karoly D, Phipps S, Wanner H, Curran M, Elbert J, Gonzalez-Rouco F, Linsley B, Moy A, Mundo I, Raible C, Steig E, van Ommen T, Vance T, Villalba R, Zinke J, Frank D (2014) Inter-hemispheric temperature variability over the last millennium. Nature Climate Change. doi:10.1038/nclimate2174

Esper J, Frank DC, Timonen M, Zorita E, Wilson RJS, Luterbacher J, Holzkämper S, Nievergelt D, Verstege A, Büntgen U (2012) Millennial-Length Temperature Reconstructions Adjusted for Orbital Forcing. Nature Climate Change. doi:10.1038/nclimate1589.

Treydte K, Schleser GH, Helle G, Frank DC, Winiger M , Haug GH, Esper J (2006) The 20th-century was the wettest period in Northern Pakistan over the past millennium. Nature. 440, 1179-1182. doi:10.1038/nature04743

Hemispheric temperature reconstructions and model simulations

In the upper panel, reconstructions of Northern Hemisphere temperatures are shown in orange and a new ensemble of Southern Hemisphere temperature reconstructions in blue. The lower panel shows the same for model simulations.
Note that both the models and reconstructions show warmth during the most recent decades is unprecedented within the past millennium. (Source: Neukom et al. 2014 Nature Climate Change). Click on picture to enlarge.