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Comparative Study
. 2005 May 24;102(21):7465-9.
doi: 10.1073/pnas.0502286102. Epub 2005 May 17.

Human-modified temperatures induce species changes: Joint attribution

Terry L Root  1 , Dena P MacMynowski, Michael D Mastrandrea, Stephen H Schneider
Affiliations
Comparative Study

Human-modified temperatures induce species changes: Joint attribution

Terry L Root et al. Proc Natl Acad Sci U S A. .

Abstract

Average global surface-air temperature is increasing. Contention exists over relative contributions by natural and anthropogenic forcings. Ecological studies attribute plant and animal changes to observed warming. Until now, temperature-species connections have not been statistically attributed directly to anthropogenic climatic change. Using modeled climatic variables and observed species data, which are independent of thermometer records and paleoclimatic proxies, we demonstrate statistically significant "joint attribution," a two-step linkage: human activities contribute significantly to temperature changes and human-changed temperatures are associated with discernible changes in plant and animal traits. Additionally, our analyses provide independent testing of grid-box-scale temperature projections from a general circulation model (HadCM3).

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Figures

Fig. 1.
Fig. 1.
For each year, the occurrence dates (Julian) of spring phenological traits are averaged over all Northern Hemisphere species exhibiting statistically significant changes in those traits (n = 130). These averages are plotted against the following. (A) Year with a –3.2 day change per decade. (B) The average modeled spring (March, April, and May) temperatures including only natural forcings at each study location (r = 0.22, P < 0.23). (C) Identical to B but including only anthropogenic forcings (r = –0.71, P < 0.001). (D) Identical to B but including both natural and anthropogenic forcings (r = –0.72, P ≤ 0.001).
Fig. 2.
Fig. 2.
Frequency of correlation coefficients calculated between species' phenological traits and modeled spring (March, April, and May) temperatures for all species showing phenological changes (n = 145) assuming NF (A), AF (B), or CF (C). The striping indicates that all of the indicated correlation values are statistically significant (P < 0.1).
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