You cannot point at a single weather event and say that climate change is responsible for it. Weather has always happened, even before there was manmade climate change. But, a pattern of events can be used to paint a picture. That is what we are now seeing.
Weather in the U.S. has been very extreme the last few years. A notable example of this is the severe drought that was experienced in Texas. It may have been the most severe drought every recorded in Texas and covered almost the entire state. This, deniers will say, was the result of naturally occurring weather patterns. Texas has had droughts before and will have them in the future. While this statement is true, it is not complete. What we are seeing is the number and severity of Texas droughts are both increasing. These increases correlate with the rise in global temperatures.
Texas and the U.S. are not the only places to experience severe weather the last few years. It has been a worldwide phenomenon. Some of this is natural. Some of the disasters are actually manmade without global climate change. By changing water drainage humans caused the extensive flooding in Thailand last year in what would have been an otherwise relatively normal event.
But some of the extreme weather can be attributed to global warming.
The basic lesson is that the world's weather system is a heat engine. At a fundamental level, it takes in energy and produces weather. Add more energy and you get more weather. Add lots more energy and you get lots more weather. Crank up the energy and you crank up the engine.
Now, this year, the Midwest U.S. is having a drought. It is so severe that it is affecting the crops, which is sure to have an impact on food prices later on. Now, farmers in Nebraska using surface water are told to stop irrigating. That isn't going to help.
As global temperatures continue to rise we will see weather that is more severe and we will see it more often.