The circular fields of green are the result of pivot irrigation in the desert of Saudi Arabia. In a new study, Puma, M. J., and B. I. Cook (2010), Effects of irrigation on global climate during the 20th century, J. Geophys. Res.,
115, D16120, it is suggested that widespread irrigation is altering local weather patterns and probably masking the effects of global warming through a process that reduces surface temperature via changes to the Bowen ratio. Just another example of how complex the climate system really is.