This report by the minority staff of the House Committee on Natural Resources lays out the case for believing that recent weather extremes, such as storms, disasters, heat waves, and drought, are being caused by global warming and climate change. The report states:
Scientists have been investigating the link between extreme weather events and man-made global warming for years. They now generally agree that global warming pollution plays a role, along with natural factors such as El Nino or La Nina, in shifting the odds toward extreme events. In fact, NOAA recently concluded, after looking through 50 years of weather data, that droughts like the record 2011 Texas drought was made "roughly 20 times more likely" because of global warming. Indeed, observations have shown that certain extremes—high heat, heavy precipitation and floods, duration and intensity of droughts and extremes related to higher sea levels—have increased over the last half of the century.
Global warming has stacked the deck with extra jokers, making some weather events more frequent and severe and increasing the chances of an event far outside the norm.
The multitude of extreme weather events in the United States during 2012 are consistent with scientists' understanding that global warming is increasing the odds of heat waves, heavy precipitation, droughts and wildfires.