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23 October 2009

Higher trends but larger uncertainty and geographic variability in 21st century temperature and heat waves

Published online before print September 8, 2009, doi: 10.1073/pnas.0904495106
PNAS September 15, 2009 vol. 106 no. 37 15555-15559

Higher trends but larger uncertainty and geographic variability in 21st century temperature and heat waves
Auroop R. Gangulya,1, Karsten Steinhaeusera,b, David J. Erickson IIIc, Marcia Branstetterc, Esther S. Parisha, Nagendra Singha, John B. Drakec and Lawrence Bujad
+ Author Affiliations

aGeographic Information Science and Technology Group, Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831;
bDepartment of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556;
cComputational Earth Sciences Group, Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831; and
dNational Center for Atmospheric Research, Boulder, CO 80305
Edited by Stephen H. Schneider, Stanford University, Stanford, CA, and approved July 31, 2009 (received for review April 23, 2009)

Abstract
Generating credible climate change and extremes projections remains a high-priority challenge, especially since recent observed emissions are above the worst-case scenario. Bias and uncertainty analyses of ensemble simulations from a global earth systems model show increased warming and more intense heat waves combined with greater uncertainty and large regional variability in the 21st century. Global warming trends are statistically validated across ensembles and investigated at regional scales. Observed heat wave intensities in the current decade are larger than worst-case projections. Model projections are relatively insensitive to initial conditions, while uncertainty bounds obtained by comparison with recent observations are wider than ensemble ranges. Increased trends in temperature and heat waves, concurrent with larger uncertainty and variability, suggest greater urgency and complexity of adaptation or mitigation decisions.

climate change extremes regional analysis
Footnotes

1To whom correspondence should be addressed. E-mail: gangulyar@ornl.gov
Author contributions: A.R.G. designed research; A.R.G. and K.S. performed research; D.J.E., M.B., J.B.D., and L.B. contributed new reagents/analytic tools; K.S., E.S.P., and N.S. analyzed data; and A.R.G., K.S., and D.J.E. wrote the paper.
The authors declare no conflicts of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0904495106/DCSupplemental.

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