STOCKHOLM — Though you can't make a direct link between Australia's killer floods and climate change, they do hold a warning for the future: Scientists predict such extreme weather events will increase both in intensity and frequency as the planet warms.
Raging floodwaters have swamped thousands of homes and businesses in Queensland, leaving at least 25 people dead and dozens more missing since late November. Rail lines and highways have been washed away in what is shaping up to become Australia's costliest natural disaster.
The flooding follows a spate of severe natural disasters in the past year. While the most deadly was Haiti's earthquake, extreme weather also killed thousands of people across the globe, including a scorching heat wave that choked Russia in the summer and devastating floods that engulfed more than 60,000 square miles (150,000 square kilometers) in Pakistan.
"The Earth is delivering a message to us. And the message is that more extreme weather is becoming the norm rather than the exception," said John Magrath, a climate change researcher at British charity Oxfam.
He said there is a misconception that global warming only means higher temperatures. "It actually means more energy in the climatic system, which stimulates extremes and more chaotic behavior," Magrath said.
Droughts and floods are expected to become more severe as global temperatures climb. Less clear is the impact on wind patterns and ocean currents, factors that could alter climate in potentially dramatic ways not fully understood yet.
Last year tied with 2005 as the warmest on record, with combined global land and ocean surface temperatures rising 1.12 degrees Fahrenheit (0.62 degrees Celsius) above normal, the National Oceanic and Atmospheric Administration said Wednesday.
In the U.S., it was the 23rd warmest year on record and the 14th year in a row with an annual temperature above the long-term average, according to NOAA's preliminary analysis.
Meanwhile, the extent of Arctic sea ice in the summer – a key indicator of global warming – was at its third lowest level, behind 2007 and 2008.
Most atmospheric scientists attribute most of the warming seen in recent decades to gases released into the air by industrial processes and gasoline-burning engines.
Australia's floods, which started in late November, have been linked to the La Nina weather phenomenon, which refers to cooler than normal surface sea temperatures in parts of the Pacific, causing disruptions in weather patterns. La Nina occurs naturally, and the link to climate change remains unclear, said Omar Baddour of the World Meteorological Organization.
"But as we know, extreme events whether their cause is due to La Nina or El Nino or other factors, will be more intense in the era of climate change," he added.
Reinsurer Munich Re counted nearly 1,000 natural disasters in 2010 – nine-tenths of them weather-related – the second highest number since 1980. The resulting economic losses totaled $130 billion, the German company said earlier this month.
"The high number of weather-related natural catastrophes and record temperatures both globally and in different regions of the world provide further indications of advancing climate change," Munich Re said.
Scientists caution against drawing conclusions about climate change from a single storm, flood, cold snap or heat wave. Natural variability is and will always be a factor when it comes to extreme weather.
Still, single events can be useful in highlighting shortcomings in our preparedness for a warmer world more prone to extremes, said Markku Rummukainen, a climate scientist at Lund University in Sweden.
"For example, that Hurricane Katrina hit New Orleans does not have to have anything to do with climate change, but it revealed vulnerabilities that hadn't been considered," said Rummukainen, who is also involved in drafting the next report by the U.N.'s expert panel on climate change. "It remains to be seen what conclusions can be drawn in Australia."