Dynamical evidence for causality between galactic cosmic rays and interannual variation in global temperature.
As early as 1959, it was hypothesized that an indirect link between solar activity and climate could be mediated by mechanisms controlling the flux of galactic cosmic rays (CR) [Ney ER (1959) Nature 183:451-452]. Although the connection between CR and climate remains controversial, a significant body of laboratory evidence has emerged at the European Organization for Nuclear Research [Duplissy J, et al. (2010) Atmos Chem Phys 10:1635-1647; Kirkby J, et al. (2011) Nature 476(7361):429-433] and elsewhere [Svensmark H, Pedersen JOP, Marsh ND, Enghoff MB, Uggerhøj UI (2007) Proc R Soc A 463:385-396; Enghoff MB, Pedersen JOP, Uggerhoj UI, Paling SM, Svensmark H (2011) Geophys Res Lett 38:L09805], demonstrating the theoretical mechanism of this link. In this article, we present an analysis based on convergent cross mapping, which uses observational time series data to directly examine the causal link between CR and year-to-year changes in global temperature. Despite a gross correlation, we find no measurable evidence of a causal effect linking CR to the overall 20th-century warming trend. However, on short interannual timescales, we find a significant, although modest, causal effect between CR and short-term, year-to-year variability in global temperature that is consistent with the presence of nonlinearities internal to the system. Thus, although CR do not contribute measurably to the 20th-century global warming trend, they do appear as a nontraditional forcing in the climate system on short interannual timescales.
Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201; aatsonis@uwm.edu robert.may@zoo.ox.ac.uk gsugihara@ucsd.edu.
Anastasios A
AA
Tsonis
Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093;
Ethan R
ER
Deyle
Department of Zoology, University of Oxford, Oxford OX1-3PS, United Kingdom; and aatsonis@uwm.edu robert.may@zoo.ox.ac.uk gsugihara@ucsd.edu.
Robert M
RM
May
Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093; aatsonis@uwm.edu robert.may@zoo.ox.ac.uk gsugihara@ucsd.edu.
George
G
Sugihara
Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201;
Kyle
K
Swanson
Department of Mathematical Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201;
Joshua D
JD
Verbeten
Key Laboratory of Middle Atmosphere and Global Environment Observations, Institute for Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China.
Geli
G
Wang
causality; climate variability; convergent cross mapping; cosmic rays; global temperature