Tom Nelson captures this delicious irony, apparently it isn’t a travesty any more, it’s the sun.
[Trenberth] “Warming” really means heating, and so it can be manifested in many ways. Rising surface temperatures are just one manifestation. Melting Arctic sea ice is another. So is melting of glaciers and other land ice that contribute to rising sea levels. Increasing the water cycle and invigorating storms is yet another…Another prominent source of natural variability in the Earth’s energy imbalance is changes in the sun itself, seen most clearly as the sunspot cycle. From 2005 to 2010 the sun went into a quiet phase and the warming energy imbalance is estimated to have dropped by about 10 to 15%.
…Human induced global warming really kicked in during the 1970s, and warming has been pretty steady since then…Focusing on the wiggles and ignoring the bigger picture of unabated warming is foolhardy, but one promoted by climate change deniers. Global sea level keeps marching up at a rate of over 30 cm per century since 1992 (when global measurements via altimetry on satellites were made possible), and that is perhaps a better indicator that global warming continues unabated.
[Trenberth in Climategate1, 2009] The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t.
Uncertainty about “invigorating storms” must be the new unaccountable travesty.
From an interview after the Moore, OK tornado in Scientific American:
[Q:] I know this kind of extreme weather is part of the territory in the middle of the country, but is climate change going to make such extreme weather more likely or more powerful?
[A: Trenberth] Of course, tornadoes are very much a weather phenomenon. They come from certain thunderstorms, usually supercell thunderstorms that are in a wind shear environment that promotes rotation. That environment is most common in spring across the U.S. when the storm track is just the right distance from the Gulf [of Mexico] and other sources of moisture.
The main climate change connection is via the basic instability of the low-level air that creates the convection and thunderstorms in the first place. Warmer and moister conditions are the key for unstable air. The oceans are warmer because of climate change.
The climate change effect is probably only a 5 to 10 percent effect in terms of the instability and subsequent rainfall, but it translates into up to a 33 percent effect in terms of damage. (It is highly nonlinear, for 10 percent it is 1.1 to the power of three = 1.33.) So there is a chain of events, and climate change mainly affects the first link: the basic buoyancy of the air is increased. Whether that translates into a supercell storm and one with a tornado is largely chance weather.