Global is new local

It turns out that the residents of Beijing and Delhi are not the only ones feeling the effects of their cities’ air pollution - an unwanted by-product of coal-fired economic development.

Researchers looking at how Asian pollution is changing weather and climate around the globe and have found pollution from China affects cloud development in the North Pacific and strengthens extra-tropical cyclones.

These large storms punctuate US winters and springs about once a week, often producing heavy snow and intense cold.

Tainted air is known to cross the Pacific Ocean, adding to homegrown air-quality problems on the US West Coast. But now scientists say the story doesn’t stop there - because pollution doesn't just pollute.

Researchers at NASA's Jet Propulsion Laboratory (JPL) and the California Institute of Technology, both in Pasadena, California, are looking at how Asian pollution is changing weather and climate around the globe.

Scientists call airborne particles of any sort - human-produced or natural - aerosols. And the simplest effect of increasing aerosols is to increase clouds.

To form clouds, airborne water vapour needs particles on which to condense. With more aerosols, there can be more or thicker clouds.

During the last 30 years, clouds over the Pacific Ocean have grown deeper, and storms in the Northwest Pacific have become about 10 percent stronger. This is the same time frame as the economic boom in Asia.

JPL researcher Jonathan Jiang and his postdoctoral fellow, Yuan Wang, designed a series of experiments to see if there was a connection between the two phenomena.

They used a numerical model that included weather factors such as temperature, precipitation and barometric pressure over the Pacific Ocean as well as aerosol transport - the movement of aerosols around the Earth.

They did two sets of simulations. The first used aerosol concentrations thought to have existed before the industrial revolution. The other used current aerosol emissions. The difference between the two sets showed the effects of increased pollution on weather and climate.

"We found that pollution from China affects cloud development in the North Pacific and strengthens extra-tropical cyclones," said Wang.

He explained that increased pollution makes more water condense onto aerosols in these storms. During condensation, energy is released in the form of heat. That heat adds to the roiling upward and downward airflows within a cloud so that it grows deeper and bigger.

"Large, convective weather systems play a very important role in Earth's atmospheric circulation," Jiang said, bringing tropical moisture up to the temperate latitudes. The storms form about once a week between 25 and 50 degrees north latitude and cross the Pacific from the southwest to the northeast, picking up Asia's pollutant outflow along the way.

Wang thinks the cold winter that the US east coast endured in 2013 probably had something to do with these stronger extratropical cyclones - and the intense storms could also have affected the upper-atmosphere wind pattern, called the polar jet stream.

Jiang and Wang are now working on a new experiment to analyse how increased Asian emissions are affecting weather even farther afield than North America. Although their analysis is in a preliminary stage, it suggests that the aerosols are having a measurable effect on climatic conditions around the globe.

Closer to home - a gas-fired power station in Spalding, Lincs, UK.                    Photo: Clive Simpson

Jiang says that Asian emissions have made him and some other climate researchers conceptualise Earth differently.

"Before, we thought about the north-south contrast: the northern hemisphere has more land, the Southern Hemisphere has more ocean. This difference is important to global atmospheric circulation and now, in addition, there's a west-east contrast.

“Europe and North America are reducing emissions - Asia is increasing them. That change also affects the global circulation and perturbs the climate."

Report by Clive Simpson freelance journalist

Tragedy in Nepal

Ten years ago this weekend I had just arrived in Kathmandu with my good friend, Tim Scott, where I was to start trekking for the second time amongst the wonderful high peaks and scenery of Nepal.

We joined a party of a dozen international trekkers on a three week hike that would take us across Gokoyo Ri at 5,360 m and through the 5,400 m Cho La pass before trekking to Gorak Shep and ascending the 5,500 m Kala Patar, known as the trekker’s ‘mountain’ overlooking Mt Everest and basecamp.

October in Nepal is a peak season for trekkers to gather and work their way along and up the Himalayan mountain trekking routes. Skies are normally clear by day and the sun often shines before the bitter cold returns at dusk.

But the tragedy that unfolded in Nepal this week was on an altogether unprecedented scale. A series of avalanches followed heavy snowfall and blizzard conditions on Tuesday causing a a nightmare scenario with at least 32 people dead and many more missing.

Most of the fatalities happened as the blizzard reached a point on the Annapurna Circuit 100 miles northwest of the capital, Kathmandu. This too is a well-known trekking route in central Nepal and at about 4,500 m it is close to the circuit’s highest point, the Thorung La pass.

Tourists from countries around the world were caught on the mountain and helicopters saved more than 200 survivors stranded in lodges and huts along the route, according to Nepales authorities.

With snowfall from the storm topping six feet in some places, this is probably the worst disaster in the history of Nepal’s trekking business.

The blizzard was the tail end of cyclone Hudhud, which hit the Indian coast a few days earlier and was reportedly one of the strongest storms on record to affect the region. It made landfall in Andhra Pradesh, India, last Sunday and was the equivalent of a category four hurricane.

Scientists are always reluctant to link any one weather event to climate change but they have pointed out in the past that the Himalayas are especially vulnerable to the increased storm intensity expected to result from climate change.

“Storms in that region are getting stronger,” John Stone, an IPCC lead author and adjunct professor at Carleton University in Ottawa, told the Toronto Star. “It is not inconsistent with what scientists have been saying - by making the atmosphere contain more energy, we have increased the likelihood of more frequent and severe storms.”

The International Centre for Integrated Mountain Development, a regional agency based in Kathmandu that serves eight countries, released a report in May showing that rising temperatures caused Nepal’s glaciers to shrink by almost a quarter between 1977 and 2010 - at an average loss of about 15 square miles per year.

The report also pointed out that Nepal’s average temperature change has been two to eight times greater than the global average and says such changes could bring more intense and frequent floods, avalanches and landslides.

In April this year an avalanche - caused by melting ice from the Khumbu ice fall - killed 16 Nepalese guides near Mt Everest base camp in one of the deadliest disasters in the mountain’s history.

Modern  weather forecasting has reduced the risk of being surprised by a killer storm like the one that struck last weekend but the pronounced warming of the Himalayan climate in recent years has made the icefall more unstable than ever and added to the dangers for both trekkers and mountaineers.

A former British Gurkha officer and avid trekker General Sam Cowan is quoted as saying that “no one should have ventured out to cross Thorung La with the weather as threatening as it was”.

But access to our accustomed news media and forecasts is not always so easy in the high and remote mountains and it is unclear at this stage whether those caught in the storm had the benefit of any warning or not.

 

 

All photos: Clive Simpson