Deep freeze, heatwave, flash floods: What on earth is going on with the weather?
A record deep-freeze in the United States, severe flash floods in Singapore, a blistering heatwave in Sydney, record low temperatures in normally balmy Bangladesh and a severe cold snap across large parts of China. And now blizzards in Hokkaido, while Tokyo basks in unusually warm weather.
With each passing year, the weather seems to become more extreme, with wild weather making major headlines and breaking new records. And scientists say climate change is increasingly to blame.
That's because the planet's atmosphere and oceans are heating up. Warmer air holds more moisture, bringing more rain and snow. Warmer oceans provide more fuel to power storms.
In short, climate change is giving the weather an extra kick and is also affecting atmospheric circulation, such as high-altitude jet streams, in ways scientists still don't fully understand.
EVIDENCE
There is strong scientific evidence that human-caused climate change caused by burning fossil fuels and deforestation is increasing the intensity of heatwaves, droughts and coastal flooding.
Intense heat and longer droughts are also a recipe for more severe bushfires in places such as South-East Australia and California.
Leading climate scientist Michael Mann, professor of atmospheric science at Penn State University in the United States, explained it simply last year during a presentation published by Climate Reality.
"There are various ways in which climate change can make weather more extreme. Some of them are fairly obvious - if you warm up the planet, you're going to have more frequent and intense heatwaves. Warmer planet, you're going to have more extremely hot days. You tend to see more flooding events, because a warmer atmosphere can hold more moisture, so when it does rain or snow, you actually get more precipitation. The rain and snow falls in larger amounts, and that's something we've seen as well in recent years."
In a study published in 2016 by the UN's World Meteorological Organization, the authors pointed to strong links to climate change exacerbating extreme floods in Britain in 2014 and a severe summer in Australia in 2013.
The authors cited a scientific analysis showing the record heat that summer was made at least five times more likely - a 500 per cent increase in the odds of it occurring - by human-caused warming.
The authors also cited an analysis that concluded climate change had increased the chances of the rainfall behind the 2014 floods by an estimated 43 per cent.
SINGAPORE NOT SPARED
Singapore, too, will face more extreme conditions as the world warms.
The island will not be spared of flash floods, extended dry spells or warm periods.
Experts told The Straits Times that the concerns for Singapore would be increased frequency of droughts and flash flooding, due to increased rainfall over the years.
Government statistics already show a trend of increasingly intense rainfall over the years. The annual maximum hourly rainfall was 80mm in 1980, and 90mm in 2016.
The hottest years in Singapore also took place within the past decade. The year 2016 was Singapore's hottest year, with the annual mean temperature rising to 28.4 deg C. In 2015, 1998 and 1997 - the three other warmest years here - the annual mean temperature was 28.3 deg C.
In the future, the forecast is likely to see higher average annual rainfall, more intense bursts of rain and a greater contrast between the wet months of January to February and the dry months of February and June to September, the government says.
Sea levels, too, are also rising around the island, which is why the government has implemented policies to raise the height of new reclamations.
CLIMATE LINK TO DEEP FREEZE?
But what about the bitter cold snap that has frozen the eastern US? Is that linked to climate change?
Some scientists studying the connection between climate change and cold spells, which occur when cold Arctic air dips south, say that they may be related. But the importance of the relationship is not fully clear yet, the New York Times reported.
The Arctic is not as cold as it used to be - the region is warming faster than any other - and studies suggest that this warming is weakening the jet stream, which ordinarily acts like a giant lasso, corralling cold air around the pole.
The reason a direct connection between cold weather and global warming is still up for debate, scientists say, is that there are many other factors involved. Ocean temperatures in the tropics, soil moisture, snow cover, even the long-term natural variability of large ocean systems all can influence the jet stream.
"There's a lot of agreement that the Arctic plays a role, it's just not known exactly how much," the New York Times quoted Marlene Kretschmer, a researcher at the Potsdam Institute for Climate Impact Research in Germany, as saying. "It's a very complex system."
But one thing is clear, scientists say. When there are weaker temperature gradient between the Arctic and mid-latitudes, the result is weaker winds. Ordinarily the jet stream is straight, blowing from west to east. When it becomes weaker it can become wavy. That makes it more susceptible to disturbances, such as a zone of high pressure that can force colder air southward.
These "blocking" high-pressure zones are often what creates a severe cold spell that lingers for several days or longer, the New York Times said.
As the world continues to warm and as more heat-trapping greenhouse gases are pumped into the atmosphere, expect more weather extremes, scientists say. It's the new normal.
Additional reporting by Audrey Tan
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