Smoky Sun and Moon

The full moon was spectacular where it was visible through the smoke and now clouds. New wildfires broke out across east Central Florida today closing some main roads (SR 40 west of Ormond Beach).



The largest area fire is near the lake house in Deltona at 1,200 acres in the Maytown-Osteen area. Ash was falling on me all afternoon as I tended the gardens and the wildlife.



The sun tried to peek through the smoke but it was mostly just an orange ball. . .



especially as some tall storms built to the west in the late afternoon.



Unfortunately we did not get any of the rain from those nearby thunderstorms.



WICKED DROUGHT

While this is not an unprecedented event for Florida is was brought on in part by the most extreme spring on record for precipitation in the U.S.A.

Nature's fury reached new extremes in the U.S. during the spring of 2011, as a punishing series of billion-dollar disasters brought the greatest flood in recorded history to the Lower Mississippi River, an astonishingly deadly tornado season, the worst drought in Texas history, and the worst fire season in recorded history. In Florida we experienced our 24th driest March-May period since record keeping began.



There's never been a spring this extreme for combined wet and dry extremes in the U.S. since record keeping began over a century ago, statistics released last week by the National Climatic Data Center (NCDC) reveal. Their Climate Extremes Index (CEI) looks at the percentage area of the contiguous U.S. experiencing top 10% or bottom 10% monthly maximum and minimum temperatures, monthly drought, and daily precipitation. During the spring period of March, April, and May 2011, 46% of the nation had abnormally (top 10%) wet or dry conditions--the greatest such area during the 102-year period of record. On average, just 21% of the country has exceptionally wet conditions or exceptionally dry conditions during spring. In addition, heavy 1-day precipitation events--the kind that cause the worst flooding--were also at an all-time high in the spring of 2011. However, temperatures during spring 2011 were not as extreme as in several previous springs over the past 102 years, so spring 2011 ranked as the 5th most extreme spring in the past 102 years when factoring in both temperature and precipitation.

In other words. . . it could have been worse. . . and it could get worse. . .

So what is causing this extreme weather?

Most climate scientists believe it is a combination of a waning La Niña episode in the Eastern Pacific coupled with climate change brought on by an exploding human population the world over. . . and in turn the burning of fossil fuels to satisfy the needs of those humans.

Below: Spring temperature rankings. Note that it was one of the warmest springs on record (in the past 117 years). for much of the South and east of the continent.



So can we say with any certainty that climate change was involved?

Whenever an unprecedented series of extreme weather events occur, it is natural to ask how climate change may be affecting the odds of these events, since our climate is undergoing unprecedented changes. This spring's unusual precipitation pattern--wet in the Northern U.S., and dry in the South--does fit what we'd expect from a natural but unusually long-lived winter La Niña pattern. However, it also fits the type of precipitation pattern climate models expect to occur over the U.S. by the end of the century due to human-caused warming of the climate (though shifted a few hundred miles to the south. This drying of the Southern U.S. and increased precipitation in the Northern U.S. is expected to occur because of a fundamental shift in the large scale circulation of the atmosphere. The jet stream will retreat poleward, and rain-bearing storms that travel along the jet will have more moisture to precipitate out, since more water vapor can evaporate into a warmer atmosphere. The desert regions will expand towards the poles, and the Southern U.S. will experience a climate more like the desert regions of Mexico have now, with sinking air that discourages precipitation.



Above: The future: simulated change in precipitation during winter and spring for the years 2089-2099 as predicted by fifteen climate models assuming continued high emissions of heat-trapping carbon dioxide. Note that Florida will become still 25-30% drier.

A hotter climate will dry out the soil more, making record intensity droughts like this year's in Texas more probable. So, is it possible that the record extremes of drought and wetness this spring in the U.S. were due to a combination of La Niña and climate change. It is difficult to disentangle the two effects without doing detailed computer modelling studies, which typically take years complete and publish. One weakness in the climate change influence argument is that climate models predict the jet stream should retreat northwards and weaken due to climate change. Indeed, globally the jet stream retreated 270 miles poleward and weakened during the period 1970 - 2001, in line with climate model expectations. Thus, a stronger and more southerly jet stream over the U.S. during the spring is something we should expect to see less and less of during coming decades.

Below: During the past 50 years there has been a pronounced drying over the Southeast and Southwest U.S.