National Geographic: Impoverished farmers in South Asia and southern Africa could face growing food shortages due to climate change within just 20 years, a new study says. Increasing levels of greenhouse gases, including carbon dioxide, are heating up the planet, with droughts and shifting rainfall patterns predicted for many parts of the world. "The majority of the world’s one billion poor depend on agriculture for their livelihoods," said the lead author of the new study, David Lobell …