Blowing hot and cold

*Deep freeze *heatwave *flash floods: What on earth is going on with the weather?

The new year has barely started and already extreme weather is making headlines.

A record deep-freeze in the United States, severe flash floods here, a blistering heatwave in Sydney, record low temperatures in normally balmy Bangladesh, plus a severe cold snap across large parts of China. And now blizzards in Hokkaido, while just to the south, Tokyo basks in unusually mild winter weather.

With each passing year, the weather seems to become more extreme, breaking new records and generating major headlines. And scientists say climate change is increasingly to blame.

That is 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 affecting atmospheric circulation, such as high-altitude jet streams, in ways scientists do not fully understand.

EVIDENCE

There is strong evidence that climate change caused by burning fossil fuels and deforestation is increasing the intensity of heatwaves, droughts and coastal flooding.

Extreme heat and longer droughts also mean 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 US, explained the link 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," Dr Mann said.

A 2016 study by the United Nations' World Meteorological Organisation noted strong links to climate change exacerbating a severe summer in Australia in 2013 and Britain's extreme floods in 2014.

The authors cited analysis showing the record summer heat was made at least five times more likely 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 flash floods, extended dry spells or warm periods.

Experts told The Straits Times that the concerns for Singapore would be more droughts and flash flooding, due to increased rainfall.

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 in 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 - annual mean temperature was 28.3 deg C.

Sea levels, too, are rising around the island, which is why the government is raising the height requirement for new reclamations.

CLIMATE LINK TO DEEP FREEZE?

But what about the bitter cold snap in the eastern US?

Some scientists say climate change and cold spells, which occur when cold Arctic air dips south, may be related.

The Arctic is not as cold as it used to be and studies suggest this 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 many other factors are involved. Ocean temperatures in the tropics, soil moisture, snow cover, even the long-term natural variability of large ocean systems, can all 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."

One thing is clear. 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


China renews cold front alert as heavy snow wreaks havoc

BEIJING • China has renewed its alert for a cold front as heavy snow continues to cause great damage in parts of the country, Xinhua news agency reported.

The meteorological authority on Monday evening renewed a yellow alert for a cold snap across the country.

China has a colour-coded weather warning system, with red representing the most severe, followed by orange, yellow and blue.

Temperatures in northern, north-eastern, central and southern China, including parts of Inner Mongolia and Yunnan, are expected to drop by 6 to 8 deg C today.

The lowest temperatures in parts of Shaanxi, Henan, Hubei and Anhui could reach minus 10 to minus 15 deg C, or lower, breaking historical records, Xinhua reported.

In those areas hit by heavy snow, icy roads have been closed, causing massive disruptions to traffic.

Temperatures in northern, north-eastern, central and southern China, including parts of Inner Mongolia and Yunnan, are expected to drop by 6 to 8 deg C today.

Nineteen expressways in north-east China's Liaoning province have been closed or controlled since snow started on Sunday night, according to the local transport authorities.

In Xinyang City, central China's Henan province, heavy snowfall from last Wednesday to Friday killed one person and injured three others. It was the worst since local records began in 1951, Xinhua said. Primary and secondary schools in the city have suspended classes since last Thursday.

The disaster also flattened 26 houses and damaged more than 2,000ha of crops, causing total economic losses of 219 million yuan (S$45 million), Xinhua reported.

In eastern China's Anhui province, quilts and coats have been distributed for residents to shield themselves from the biting cold, following heavy snow since last Wednesday, the worst in Anhui since 2008.

Across the country, the snow has so far affected 1.5 million people and damaged more than 160,000ha of crops. Total economic losses amounted to 3.5 billion yuan.

A version of this article appeared in the print edition of The Straits Times on January 10, 2018, with the headline 'Blowing hot and cold'. Print Edition | Subscribe