Smog replaces sunshine in China

Navneet Mendiratta

10 February 2006

The clouds in China have been replaced by the smog, one that has made the country significantly darker than it was some 50 years ago.

According to the researchers from the US Department of Energy’s PNNL (Pacific Northwest National Laboratory) in Washington, there has been a nine-fold increase in fossil fuel emissions over the same half-century period. This has resulted in China getting entrenched in a foggy haze that has absorbed and deflected the rays of the sun.

A team of researchers led by Yun Qian studied records from more than 500 weather stations across China between 1954 and 2001 and found that solar radiation has decreased by two per cent per decade since 1954.

The researchers also found that water evaporation rates across the country have also decreased in the same period by about 3.8 centimetres per decade. And this, concluded the researchers, is due to a dip in solar radiation combined with increased temperatures and wind speeds.

The researchers noted a very clear trend, which indicated that the overcast days had decreased by 0.78% in each decade while the cloud-free days had increased by 0.6% for the same period.

‘This trend strongly suggests that increasing aerosol concentrations (particles, mainly soot and sulphur, that pollute the air) in the past have produced a fog-like haze that has reduced solar radiation (surface heat from sunshine), despite more frequent clear days that should lead to increased solar radiation,’ said the co-author and PNNL fellow Ruby Leung in PNNL’s official release.

For comparison, the researchers quoted last year’s Science report that showed that most of the planet’s surface is brightening. The report had attributed this to air-pollution regulation throughout most of the industrialized world. The report even showed a curious blip in surface brightness in China in mid-1990s.

‘However, the air pollution in China has not decreased in the 1990s, so it is not clear if the short-term increasing trend in solar radiation in China is due to cleaner air, as the Science report suggested,’ Qian said.

But what is worrying the researchers is that considering the growing population and economic activity, the pollution outlook is only likely to get darker. ‘And haze does not only block the solar radiation, it is also infamous for acid rain and respiratory diseases,’ said Qian.

The researchers say that the haze has masked the effects of global warming across large parts of China, particularly in the central and eastern regions, where daily high temperatures have actually been decreasing. And while this may appear as good news, researchers point that any success China has in curbing emissions will accelerate the effects of global warming in those areas when cooling is unmasked.

To add to the concern, last year’s PNAS (Proceedings of the National Academy of Sciences) report on haze, or ‘atmospheric brown clouds’, in South Asia had held air pollution responsible for disrupting water cycle. The research said that as less radiation reaches the surface, the atmosphere may become more stable and clouds more persistant than usual, and less water will evaporate from the surface. As a result less water vapour is available for clouds or precipitation.

Going by the findings, the PNAS had warned that if the emission trends continue to grow, the subcontinent will face twice as many droughts in the next decade. A cause for grave concern.