New Video: Weather? or Climate Change?

September 8, 2016

After a summer of high profile extreme weather events across the US, and the world, weather experts have been hearing one question more than any other – “Is this weather, or climate change?”

When I interviewed TV weathercasters in June, I asked the question myself. Here, TV Met Dan Satterfield answers, with help from leading Atmospheric and ocean scientists.

Climate.gov:

..heavy downpours along the Gulf Coast of the United States have increased since the middle of the last century. That trend is consistent with what climate experts have predicted would happen as greenhouse gases warmed the planet: more water vapor in the air to fuel extremely heavy rain.

By itself, that general connection isn’t conclusive evidence that global warming had a hand in the mid-August downpour in Louisiana. Now, however, a preliminary analysis of the event led by climate scientists at NOAA’s Geophysical Fluid Dynamics Laboratory found that warming due to greenhouse gases has made—conservatively—events like the one in August at least 40% more likely and 10% more intense.

la_rain_summaryfinal_620

Because the devastating flooding occurred due to the rainfall over the entire region, the scientists drew a geographical box around the part of the Gulf Coast impacted by the event, and studied the three-day rainfall totals in the region for the period from August 12-14. Over this region, observations indicate that rainfall amounts observed during the event usually happen somewhere in the region about once every 30 years. At any local site, the extreme rainfall totals were closer to 1-in-500 year events.

baton-rouge-floods-620-revised

Precipitation totals (inches) from August 8-15, 2016. Over two feet of rain was observed in parts of southeastern Louisiana which led to catastrophic flooding, especially in areas around Baton Rouge. NOAA Climate.gov map based on data from AHPS.

 

extremprecipobs

extremerainpredict

Predicted changes in the annual number of days of extreme rainfall across the United States by 2041-2070 as compared to 1971-2000 if greenhouse gases continue to increase at a high rate. By mid-century, some places could experience two or more additional days per year on which the rainfall totals exceed the heaviest rains historically experienced in the area. Maps by NOAA Climate.gov, based on downscaled CMIP3 multi-model data provided by Katharine Hayhoe.

NYTimes:

Climate scientists have long said that a warming atmosphere and oceans should lead to more intense and frequent rainstorms, because there will be greater evaporation, and warmer air holds more moisture. But until recent years most scientists have said it was not possible to link any single event to climate change.

Climate scientists have long said that a warming atmosphere and oceans should lead to more intense and frequent rainstorms, because there will be greater evaporation, and warmer air holds more moisture. But until recent years most scientists have said it was not possible to link any single event to climate change.

 

louisianaflood815

Aerial photo on the left of Denham Springs, Louisiana at the height of the flooding on August 15, 2016, collected by NOAA’s National Geodetic Survey at sites identified by NOAA’s National Weather Service and the Federal Emergency Management Agency. The photo on the right was taken three days later when flood waters had receded

That is changing with the development of attribution studies, which use statistical analysis and climate modeling to compare the likelihood of an event occurring before industrialization, when there were essentially no greenhouse-gas emissions, and now, when the world is putting tens of billions of tons of carbon dioxide into the air each year.

Normally such studies can take months, largely because of the computer time required to run climate simulations. But the Louisiana study is the latest “rapid-response” research intended to determine the effect, if any, of climate change as close to the event as possible, to help inform policy makers and the public.

To speed the research, World Weather Attribution, the loose-knit research team that conducted this study, used models that have already been run. They were developed by NOAA scientists at the Geophysical Fluid Dynamics Laboratory in Princeton, N.J., and are sophisticated enough to capture the many different elements that contribute to weather in the Gulf Coast region, said Karin van der Wiel, a research associate at the laboratory.

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