• 
• 

Published on October 29, 2007

Wonder why you have difficulty sleeping? Stress or an associated medical condition are often the cause.

An atmospheric scientist recently suggested steadily rising temperatures at night might also be contributing to restless nights.

Atsamon Limsakul, a climate-change researcher at the environmental research and training centre of the Environ-mental Quality Promotion Department, examined 50-plus years of meteorological records.

Like other studies around the world, he found average temperatures in this country were on the rise.

Of particular concern is that the minimum temperature has risen at a much faster rate than the maximum temperature, which may be affecting our psyche.

"The rise in maximum and minimum temperatures at different rates has caused a progressive narrowing of daily temperature ranges, meaning the night does not become much cooler than day," Atsamon explained.

"High temperatures cause stress, especially for those living in urban areas. When the temperature does not drop much at night, bodies can't cool down from the heat. The stress that accumulates from the daytime is more likely to stay with us through the night," he added.

"Temperature also plays a crucial role in regulating biological processes such as metabolism. What will happen to us and other species on the planet when our nights are no longer cool and winters no longer get cold?"

Between 1951 and 2003, Atsamon found maximum temperatures rose only slightly - by 1.9 degrees Celsius. But the minimum temperature climbed at a much faster rate of 4.9 degrees. This was the case at almost all Meteorological Department measuring stations scattered across 32 locations.

Atsamon's report will be published in the US Journal of Atmospheric Research next month. The paper is co-authored by Dr Joaquim Goes from the Bigelow Laboratory of Ocean Science in the United States.

"The data suggest the minimum temperature in Thailand has been on the rise at an unprecedented rate since the early 1950s and has occurred at a faster rate than the maximum," Atsamon wrote.

"Similar long-term changes over the past few decades have been reported in other regions, including Asia-Pacific, the United States, China, New Zealand and most parts of Europe."

The findings are constant with European computer models, which have long predicted future night temperatures will increase at a faster rate than temperatures during the day.

Seasonally, a trend toward warmer and shorter winters - as predicted by several computer models - is already becoming evident in Thailand, the Meteorological Department's Jongkolnee Yusabai said.

Average temperatures last November and December were the highest ever recorded. They were, by 1.7 and 1 degrees respectively, above the average for the same months in the 56-year record.

The number of cool days - those days with temperatures below 16 degrees - decreased in the past five decades. Jongkolnee said a met station in Chiang Rai recorded just 70 cool days last year, compared with 90 in 1951.

At the slightly lower latitudes of Nakhon Sawan, the records showed only seven cool days last year, down from 23 days in 1951.

So what's happening to our winters? Atsamon found the increasing trend of minimum temperatures in Thailand bears a strong resemblance to global-warming patterns experienced elsewhere. However, he said more studies were needed before such a conclusion could confidently be drawn.

The scientist's primary observation is that there are significant indications that El Nino and La Nina, the dry and wet climate cycles, are an important source of variability of surface air temperature in Thailand. Higher temperatures generally occur during the El Nino years. The 1980s and 1990s experienced more frequent El Nino and fewer La Nina events than previously.

"Climate scientists around the world are still debating a chicken-and-egg situation: is global warming responsible for the increased El Nino frequency or is it the other way around? There is no concrete conclusion so far," Atsamon said.

Meanwhile, Atsamon does not rule out the impact from non-climatic factors, such as the heat-island effect from urbanisation.

Buildings, for example, both absorb more solar heat than natural surfaces and take more time to release the trapped heat. However, since his analysis includes temperature records from rural areas, the urban heat-island effect can only partially explain the warming pattern.

To better understand the causes, Atsamon is taking his studies further. He is taking part in an assessment of extreme weather events in Thailand led by Dr Sangchan Limjirakan of Chulalongkorn University's Environmental Research Institute. The study is funded by the Thailand Research Fund.

"This time I'm gathering additional records from more than 150 monitoring stations to look at detailed temperature changes at the daily level, as well as rainfall and humidity," he said.

"The purpose is to identify areas in Thailand most vulnerable to extreme weather events to guide national policy on adaptation to climate change."

Nantiya Tangwisutijit

 The Nation