Post image for Is Flood Magnitude in the USA Correlated with Global CO2 Levels?

No — or, more precisely, not  yet — conclude R.M. Hirsch and K.R. Ryberg of the U.S. Geological Survey in a recent study published in Hydrological Sciences Journal.

“One of the anticipated hydrological impacts of increases in greenhouse gas concentrations in the atmosphere is an increase in the magnitude of floods,” note Hirsch and Ryberg. Righto! Google “global warming” and “flood predictions,” and you’ll find more than 2.7 million sites where this hypothesis is affirmed or at least discussed. The researchers explain:

Greenhouse gases change the energy balance of the atmosphere and lead to atmospheric warming, which increases the water-holding capacity of the atmosphere, which in turn, potentially changes the amount of precipitable water.

Sounds plausible, but all weather is local or regional, and a lot more goes into making weather than average global temperature.  In addition, all flooding is local or regional, and a lot more goes into determining flood risk than local or regional weather patterns.

As Hirsch and Ryberg point out, “human influences associated with large numbers of very small impoundments and changes in land use also could play a role in changing flood magnitude,” and “at time scales on the order of a century it is difficult to make a quantitative assessment of the changes in these factors over time.”

That, however, did not stop good ol’ Al Gore from claiming that global warming is responsible for a decade-by-decade increase in the number of large floods around the world (An Inconvenient Truth, p. 106). Gore’s source was a chart from the Millennium Ecosystem Assessment (Figure 16.5, p. 448): [click to continue…]