SYDNEY, Aug. 12 (Xinhua) -- As Australia's unseasonably wet, chilly and windy winter lingers on, the other side of the world has been subjected to a summer of record-breaking heat and widespread fires.
Trying to understand the intricate relationship between such contrasting extreme conditions during this era of climate change has become a task of ever-increasing importance.
Jet streams, which are strong air currents swirling high in the Earth's atmosphere, have contributed greatly to extreme weather events worldwide in recent months, according to an eminent Australian meteorological expert.
University of Technology Sydney's (UTS) Dr Milton Speer told Xinhua that global warming in recent decades had altered the structure and position of jet streams which, in turn, has led to a slowing down of major weather systems.
Explaining the punishing conditions throughout the past few months, Speer noted that in both hemispheres, the jet streams have moved closer to the Earth's poles, meaning that the usual weather systems have either been pushed too far north or too far south to bring their usual moderating influences.
In Europe, the main cold frontal systems were too far north, he said.
"In eastern Australia during the warmer months earlier in the year, a prolonged period of moist, onshore flow containing coastal low-pressure troughs provided record rainfall," he said.
"In that case there was very little effect from drier air in cold frontal systems because they were too far south of the continent."
He also noted that higher than average sea surface temperatures near the coast, earlier this year, meant there was more moisture available to the atmosphere which caused larger rainfalls.
Throughout eastern Australia's long spell of stormy conditions, La Nina has become an all-too familiar name in weather forecasts and raises the questions as to whether that oceanic and atmospheric phenomenon is becoming more regular and more intensive.
Such questions, however, are difficult to answer, Speer said, noting that the previous strongest double La Nina years were 1973-1976 and 1915-1917, yet there was less rainfall in eastern Australia during those times.
Extreme weather specialist Dr Meagan Carney of the University of Queensland (UQ) is equally measured when it comes to making La Nina predictions.
"It is true that the number of La Nina patterns is greater than in recent years; however, we would need data quite far back to make conclusions on whether the number of returns is something that we expect for the system," she told Xinhua.
"Historical records are really the key to determining whether an extreme event, like sequential La Nina patterns, is happening more frequently," she said. "The scientific community is very careful about making conclusions on the reasons we may be observing such a change."
So, as the southern hemisphere approaches its warmer seasons, can Australians expect similar sweltering conditions that Europe and the United States have suffered?
"We have already seen an increase in days when daily maximum temperatures break records in parts of Australia including an increase in the number of consecutive hot days," Speer said.
"For example, in southwestern Australia last summer various locations broke the number of consecutive days over 40 degrees Celsius. In eastern Australia, the trend is also for increasingly hot summers with severe fire seasons."
Speer noted again that "these conditions are the result of accelerated global warming experienced in recent decades."
Carney, however, cautioned against making too many assumptions about what summer will hold in store for Australia.
"The complexity of a climate system and the influence of land masses and the sea on weather impact our ability to make conclusions on global connections of extreme weather events," she said.
"What we can say ... is that climate change has certainly had an impact on how often we observe extremes. We know the probability of experiencing extreme weather events, including heat waves and flooding events, is increasing." ■
