Here are some excerpts of articles/essays on the matter (continually updated): click this red.
Is this [high summer heat] the result of global warming—the rise in Earth's temperature fueled by increased greenhouse gases in the atmosphere?
"You can't point your finger and say, This is caused by global warming," said Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research in Boulder, Colorado.
Jim Laver, the NOAA [U.S. National Oceanic and Atmospheric Administration] climate scientist, said that anytime a summer heat wave rolls through or a hurricane hits, humans naturally want to know if global warming has something to do with it.
"It's normal to bring up those questions," he said. "And we try to explain [the answers] by the best science we have available." For now, a direct link between global warming and short-term weather events is impossible to prove, he said.