Tuesday, November 27, 2012

New paper shows extreme weather was less common over past 30 years compared to past 2 centuries

A paper published today in Environmental Research Letters reconstructs climate extreme events between 1500 and 2009 from tree ring data throughout Europe and shows extreme events have been relatively less common over the past 30 years in comparison to the past 2 centuries. The data also shows the 20th century [1900-2009] had 24 years with the climate extreme index at 2 or greater vs. 27 years during the 19th century. The paper adds to several other peer-reviewed papers demonstrating that extreme weather is less common with global warming.
Blow-up of the last 230 years from the bottom graph below. Number of extreme events shown on vertical axis. The 20th century had two highly extreme years in 1948 and 1976, whereas the 19th century had three. The 20th century had 24 years with climate extreme index => 2 vs. the 19th century had 27 years with climate extreme index => 2.

Note from the paper:
"In the pre-instrumental period, spatial patterns of reconstructed growth extremes become less distinct with decreasing site replication back in time. Yet—while we refrain from making direct comparisons with early instrumental data (e.g. Bohm¨ et al 2010)—it is clear from our results that climatically driven and spatially pervasive extensive growth extremes occurred in Europe during the past centuries." 

500 years of regional forest growth variability and links to climatic extreme events in Europe

Flurin Babst1, Marco Carrer2, Benjamin Poulter3, Carlo Urbinati4, Burkhard Neuwirth5 and David Frank1,6
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Climatic extreme events strongly affect forest growth and thus significantly influence the inter-annual terrestrial carbon balance. As we are facing an increase in frequency and intensity of climate extremes, extensive empirical archives are required to assess continental scale impacts of temperature and precipitation anomalies. Here we divide a tree-ring network of approximately 1000 sites into fifteen groups of similar high-frequency growth variability to reconstruct regional positive and negative extreme events in different parts of Europe between 1500 and 2008. Synchronized growth maxima or minima within and among regions indicate eighteen years in the pre-instrumental period and two events in the 20th century (1948, 1976) with extensive radial growth fluctuations. Comparisons with instrumental data showed that the European tree-ring network mirrors the spatial extent of temperature and precipitation extremes, but the interpretation of pre-instrumental events is challenged by lagged responses to off-growing season climate extremes. We were able to attribute growth minima in subsequent years to unfavourable August–October conditions and to mild climate during winter months associated with respiratory carbon losses. Our results emphasize the importance of carry-over effects and species-specific growth characteristics for forest productivity. Furthermore, they promote the use of regional tree-ring chronologies in research related to climate variability and terrestrial carbon sink dynamics.

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