Is recent wacky weather a sign of climatic change?
This winter's wackiness seems particularly pronounced.
The past month has seen snowstorms in Texas and the Persian Gulf, but balmy breezes and springlike temperatures in Moscow and Siberia.
Motorists have been washed off freeways by torrential rains in normally sunny Southern California and blown off the road by hurricane-force winds in Britain. Bavarian beer gardens were doing a booming business in the dead of winter, while canals were so low from dry weather in Venice that boats ran aground.
What's with the all the wacky weather? Across the country and around the world, Mother Nature is going to extremes.
Los Angeles recently received more rain in two weeks than it normally receives in a year. The rain sent a wall of mud sliding down a mountainside in Ventura County, flattening a score of houses and killing 10 people.
Heavy rains have also caused deadly landslides in San Paulo, Brazil, and Tijuana, Mexico.
On Christmas day, Brownsville, Texas, recorded its first measurable snowfall in 109 years. Other Texas cities such as Corpus Christi, Galveston and Victoria saw more snow in one night than they have had in several decades combined.
Stranger still was the snow that fell and accumulated for the first time in recorded history in the United Arab Emirates, a tiny Persian Gulf nation where temperatures normally top 120 degrees in the summer.
Meanwhile, spring came early to a broad swath of northern Europe. For nearly two weeks, Russia experienced its warmest January temperatures since weather observation began in 1879. Bears at the St. Petersburg zoo awakened from hibernation two months early and a big ice hockey match had to be called off when the rink melted. A weather station in Prague recorded its warmest January temperatures in 230 years of record keeping.
Every year has its weather extremes, but this winter's wackiness seems particularly pronounced, raising the question of whether these are random variations of nature or signals of human-induced climate change.
The short answer, said Raymond S. Bradley, director of the Climate System Research Center at the University of Massachusetts, is that scientists still don't have enough information about many kinds of weather phenomena to know for certain.
"You are always going to have some part of the world that's going to experience extreme drought, extreme low temperatures, extreme weather of some sort, but getting a hold of the whole picture and saying that this is different now from what it was 50 years ago is very hard to do," Bradley said.
The 10 warmest years since global record keeping began in the late 19th century have all occurred since 1990. Last year was the fourth warmest year, 2003 was the third warmest.
Many scientists believe these rising temperatures are too pronounced to be a natural variation in climate, but are instead the result of man-made emissions of carbon dioxide and other "greenhouse gases" that have built up in the atmosphere, trapping heat.
Climate models generally predict this heat will cause the world's hydrological cycle to speed up -- more rapid spring snow melts and greater evaporation that increases drought, but also puts more moisture into the atmosphere, leading to more severe rain and snowstorms.
Meanwhile, the frequency of Atlantic hurricanes has also increased. There were 15 named tropical storms in 2004 -- the average is 10 -- and nine of them struck the United States, including four hurricanes that ripped through Florida. The last time four hurricanes struck a single state in one year was 1886 in Texas.
But perhaps the most bizarre twist to the 2004 hurricane season was in March, when Caterina, the first recorded hurricane to develop in the South Atlantic, made landfall along the southern coast of Brazil. Scientists had thought water and air temperatures were too cold in the South Atlantic to permit the formation of hurricanes and, until Caterina, none had been recorded in 48 years of satellite observation.
The United States also experienced a record 1,717 tornadoes last year, topping the previous high of 1,424 tornadoes in 1998, which is also the warmest year on record.
"I think some scientists are now beginning to think the warming has already caused some of these changes," said Aiguo Dai, a scientist at the atmospheric research center, "but I personally don't think there is solid evidence to confirm that yet."