The case for how this flooding looks like climate change is a simple one. July, as you've probably read, was not only the warmest month this year or the warmest July on record. July, according to NASA data, was the warmest month in recorded history, stretching back 136 years.
The world is growing warmer, and that has a number of side effects. One is that higher temperatures increase the rate of evaporation, which leads to things like massive droughts. It also means more moisture in the atmosphere. A warmer atmosphere can also hold more moisture before it falls. For every 1.8 degrees Fahrenheit the temperature of the atmosphere increases, the moisture-holding capacity of the atmosphere increases 7 percent, according to the Centre for Ecology & Hydrology in the United Kingdom.
That's why climate models predict two seemingly contradictory trends: The world will get drier as the number of extreme precipitation events increases.
A government report on the anticipated effects of climate change in the Southeast shows how extreme precipitation events in the region have slowly increased as the world has gotten warmer.
It explains the why and how:
It can be seen that the frequency of extreme precipitation events has been increasing across the Southeast region, particularly over the past two decades. Five of the top ten annual values of this extreme precipitation index have occurred since 1990. Increases in extreme precipitation events are most pronounced across the lower Mississippi River Valley and along the northern Gulf Coast This trend in more intense precipitation events is seen in many other places around the world and may be tied to a warming atmosphere, which has a greater capacity to hold water vapor and therefore has the potential to produce higher rates of precipitation.
These increased precipitation events could be expected to lead to "an increased risk of flooding in urban areas of the region." Or, put in terms of what's happening now in Louisiana:
Donald Trump, who toured the area Friday (against the wishes of Louisiana's Democratic governor), doesn't accept the science behind climate change. In the past, he has regularly tweeted about how climate change isn't real and how "they" changed the name from "global warming" to "climate change" because the original name "wasn't working." (That's not what happened; Republican pollster Frank Luntz recommended the GOP use "climate change" to reinforce purported questions about the science behind it.) Trump once said China invented the idea to get the United States to add new controls on greenhouse-gas emissions. On the campaign trail, he has regularly mocked the idea and argued that the production of American coal — burned in power plants, releasing carbon dioxide gas — should be increased.
(In 2009, Trump's name appeared in an ad calling for action on climate change, but within months he was bashing the idea in the media.)
There's questionable political value in his drawing attention to the issue. Only 16 percent of his supporters think the condition of the environment is a very big problem for the nation, according to new data from Pew Research, compared to 43 percent of Clinton backers. Last summer, Pew tracked an increase in the number of people who expressed concern about climate change, with a wide partisan split on belief that human activity was responsible and on the urgency of the subject.
Few voters consider climate change to be a pressing problem, though. Gallup found that the importance of addressing climate change had a bigger gap between the parties than any other major issue they asked about. But even among Democrats, the subject was below average in importance as a candidate position.
If there were a way to bet on it, I'd happily put money on the Louisiana floods — the result of far more rain falling in the state than fell during Hurricane Katrina — being seen as an early example of the negative effects of the changing climate. In the moment, the subject is very unlikely to come up.