to be mediated by direct variation of insolation rather than cosmic rays, and concluded: "Hence within our assumptions, the effect of varying solar activity, either by direct solar irradiance or by varying cosmic ray rates, must be less than 0.07 °C since 1956, i.e. less than 14% of the observed global warming." Carslaw (2009) and Pittock (2009) review the recent and historical literature in this field and continue to find that the link between cosmic rays and climate is tenuous, though they encourage continued research. US EPA (2009) commented on research by Duplissy et al. (2009):The CLOUD experiments at CERN are interesting research but do not provide conclusive evidence that cosmic rays can serve as a major source of cloud seeding. Preliminary results from the experiment (Duplissy et al., 2009) suggest that though there was some evidence of ion mediated nucleation, for most of the nucleation events observed the contribution of ion processes appeared to be minor. These experiments also showed the difficulty in maintaining sufficiently clean conditions and stable temperatures to prevent spurious aerosol bursts. There is no indication that the earlier Svensmark experiments could even have matched the controlled conditions of the CERN experiment. We find that the Svensmark results on cloud seeding have not yet been shown to be robust or sufficient to materially alter the conclusions of the assessment literature, especially given the abundance of recent literature that is skeptical of the cosmic ray-climate linkage See also Climate change adaptation Climate change denial Climate change mitigation Climate resilience Environmental effects of aviation Notes References , pp. 332–333. Referred to by : . Open-access article. , pp. 18235–18270. Referred to by : , pp. 955–958. Referred to by : (pb: ). (pb: ). . Summary for Policymakers available in Arabic, Chinese, French, Russian, and Spanish. . Climate Change 2013 Working Group 1 website. . Archived page: The source appears to incorrectly list the Society of Biology (UK) twice. . L09820. , pp. 483–487. Referred to by : Public-domain sources External links How much of the recent increase is due to human activities? (RealClimate, 2005) Climate change and global warming (U.S. EPA) Climate change assessment and attribution Environmental impact of the energy industry Climatology