I have long stated the dangers of scientists refusing to take strong stands connecting weather events to climate change. I understand why they have done this–science is not about certainty, is ideally not too connected to politics, and you can’t 100 percent connect a specific weather event to climate change, although that is rapidly changing. But part of the problem as well is that scientists aren’t really trained to communicate their findings to the general public. What this has done in the real world is cede far too much ground to climate deniers, obscuring the facts and making doing something about climate change all the more difficult.
But it’s absolutely crucial to connect current weather events to climate change. Using the recent extreme flooding in Louisiana and other record rains Union of Concerned Scientists climate scientist Astrid Caldas makes the case as to how they are a consequence of climate change.
Louisiana, August 2016: “I’m going home to see if I have a home”.
Ellicot City, Maryland, July 2016: “Oh my god. There’s people in the water”.
West Virginia, June 2016: “23 dead, thousands homeless after devastating flood”.
What do these events (and 5 more since April 2015) have in common? They were all considered very low probability, and the National Oceanic and Atmospheric Administration’s Hydrometeorological Design Studies Center created maps of annual exceedance probabilities (AEPs) for all of them. AEP is the probability of exceeding a given amount of rainfall for a given duration at least once in any year at a given location. It is an indicator of the rarity of rainfall. These maps are created for significant storm events that typically have AEPs of less than 0.2% (i.e, exceed 500-year average recurrence interval amounts). For Louisiana, the probability analyzed was for the worst case 48-hour rainfall. For Ellicott City, it was for the worst case 3-hour rainfall. And for West Virginia, the June 23-24 event became a map for the worst case 24-hour rainfall.
In other words, just in the past 17 months, 8 rain events that are considered very low probability (i.e., less than 0.2%) occurred. Three happened in the past 3 months. Flooding like this should happen very rarely – there are AEP maps for only 18 more events, one of which was in 1913, all others having occurred since 2010. As our hearts go out to the families affected by the flooding, we may be asking; is this a series of unfortunate events? Certainly. The sheer loss of life and property is staggering, and heartbreaking. Totally unexpected? Unfortunately, the answer is hardly.
NOAA and NASA just released their global temperature data for the month of July 2016, and again, it was a record warm month. Not only the warmest July on record, but also the warmest month ever on record. According to NOAA, this is the 15th record warm month in a row, starting with May 2015. One can’t help but notice that over these 15 months, 8 rain events were off the probability charts, so to speak. Yes, climate change fingerprint is on these events, including the Louisiana flood, considered the worst natural disaster in the US since hurricane Sandy. Special conditions mainly fueled by climate change were behind this record event.
As much as local conditions affect rainfall events individually, global warming is among the main reasons why we are seeing places that never flooded before, such as Baton Rouge areas and Ellicott City, being swallowed by not only deep but very fast rising waters. Development and urbanization also play a big role in these events, as rainwater swells rivers that no longer have wide, protective margins, and hits impervious surfaces that do not allow for ground penetration – water that has nowhere to go but along streets and between buildings down the easiest path it can find, based on topology and gravity. Here and here are some good resources that elaborate on the aforesaid factors.
The 2014 National Climate Assessment stated: Heavy downpours are increasing nationally, especially over the last three to five decades. The heaviest rainfall events have become heavier and more frequent, and the amount of rain falling on the heaviest rain days has also increased. Increases in the frequency and intensity of extreme precipitation events are projected for all U.S. regions.
Even though Louisiana is not among the areas that had seen the most increase in heavy precipitation events, the Southeastern US saw an increase of 27 percent from 1958 to 2012. The straightforward explanation for heavier downpours is that warmer air can contain more water vapor than cooler air. Indeed, global measurements show that there is more water vapor in the air now. It follows that there is more water to come down when it rains. Other factors also affect precipitation patterns, which I have explored a bit further here. Even if one cannot directly attribute individual events specifically to climate change, the latter is behind an increased likelihood of them happening, and also of them becoming more extreme. Extreme rainfall is one type of extreme event on which the effects of climate change are better understood, according to a recent report by the National Academies of Sciences, Engineering, and Medicine that I explore in this blog.
Now, it’s never going to be a precise 1:1 correlation between climate change and a given event. But despite that, scientists have to send a strong message that it is climate change causing catastrophic flooding that creates havoc on communities and costs taxpayers millions or even billions of dollars in each event. It’s not only in our interests to take strong action to mitigate climate change and start preparing for the inevitable, but it’s the most important issue of our time. We can’t allow oil companies and those who want to deny climate change because they hate the dirty hippies to win the public opinion battle. With each major event, the message has to be over and over again that climate change is at least partially responsible and without a real program to fight and mitigate this, it’s going to happen over and over again. Unfortunately, we are far from even such a widespread communications strategy, not to mention a real agenda on what to do or the political will outside of a few leaders like Sheldon Whitehouse or Ed Markey to even make a stink about it.