But the growth of rice has various inputs -- water, fertilizer, seed quality -- all of which can alter yields in a more significant manner than climate change. The correlation between climate change and rice yields is valid only if it can be shown that warmer nights are not caused by confounding factors such as an urban heat island effect, said Cassman.
The Indian temperature analysis was done using temperature measurements from 120 weather stations in the country, collected between 1901 and 2007, according to Kanikicharla. Particular cities, especially in northern India, have shown cooling trends in recent years due to aerosols, which act as coolants in the atmosphere.
But the large-scale pattern of trends is toward warming, said Kanikicharla.
All 120 weather stations were close to cities with more than 100,000 people over the time measurements were taken. This reduces variability due to the urban heat island effect, in which the temperature increase in urban areas can be attributed to city surfaces trapping heat, he said.
"There is no such thing as a village, really, in India," he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500