Australian floods warn of global warming

Michael Richardson for the Straits Times 17 Jan 11;

GENERATIONS of Australians have learnt that their island-continent is a land of alternating droughts and floods. Recent prolonged rain and devastating flooding across north-eastern Australia, particularly in the state of Queensland, have underscored this heartbreaking cycle.

Weather experts have said the immediate cause is natural, attributing it to periodic fluctuations in the sea surface temperature of the central Pacific Ocean along the equator and in the air pressure of the atmosphere above.

Known as the El Nino-Southern Oscillation (Enso), it affects weather patterns in many parts of the Pacific, including Australia and South-east Asia.

Enso has two extreme phases in its typical see-saw every three to eight years. One, El Nino, is associated with hotter-than-normal temperatures and diminished rainfall. The other, La Nina, usually brings above-average wet weather and lower temperatures.

The Australian government's Bureau of Meteorology said earlier this month that the La Nina phase bringing the deluge to north-eastern Australia was the strongest since at least the mid-1970s. As a result, the country had its third wettest year on record last year.

Indonesia's Meteorological Office reported last week that rain across the far-flung island-nation would continue until June. It said the dry season, which normally starts in April and lasts until October, would start only in July.

Meanwhile, Brazil and Sri Lanka have been hit by unusually heavy and damaging downpours, just as northern Europe and much of the United States felt the bite of abnormally frigid winter weather.

Despite these bursts of wet and cold weather, two leading US climate agencies said last Wednesday that the average land and sea surface temperature last year tied with 2005 as the warmest on record, since data collection started in 1880. The global temperature was 0.62 deg C above the 20th-century average.

Attributed by many scientists to the growing release of carbon dioxide, methane and other global warming gases from human activity into the atmo-sphere, this temperature rise is happening at the same time as the natural Enso cycle.

Dr James Hansen, director of one of the US climate agencies, said the average global temperature in the past decade increased as fast as during the previous two decades, despite year-to-year fluctuations associated with Enso.

A summary on the state of the Australian climate published last year by the Meteorological Bureau and the CSIRO, Australia's leading scientific research organisation, said that in the past 50 years, the mean temperature in Australia had risen by about 0.7 deg C and was projected to increase further, by 0.6 to 1.5 deg C, by 2030.

It added that if global greenhouse gas emissions continued to grow at business-as-usual rates, the country could be 2.2 to 5 deg C hotter by 2070.

Scientists said the worldwide warming trend increases the likelihood of extreme weather events such as heat waves, droughts and floods. In addition to being the hottest year ever, last year was also the wettest on record.

A hotter world causes more evaporation from land and oceans. A warmer atmosphere holds and releases more water, which can mean more violent storms and bigger floods.

The equatorial expanse of the Pacific Ocean, which is far larger than the Indian and Atlantic oceans, is critical to the development of Enso.

During La Nina, trade winds blowing towards the west bring moist air to northern Australia and Indonesia. Heated by the tropical sun and warm water, the air rises to create towering bulbous clouds and heavy rainfall.

The question that must concern South-east Asia is whether man-made global warming from burning fossil fuels and clearing forests is intensifying natural weather patterns like Enso and, if so, how?

It is clear that if an exceptionally dry El Nino phase occurs against the backdrop of long-term man-made global warming, one will make the other even hotter. This happened in Indonesia in 1997 and 1998 during the Asian financial crisis, when forest fires spread haze pollution across South-east Asia.

Some scientists also think there is a link between the rising global sea temperature and the strength of Enso cycles.

The annual climate statement by the Australian Meteorological Bureau, issued on Jan 5, noted that sea surface temperatures in the Australian region last year were the warmest on record, 0.54 deg C above the 1961 to 1990 average. The past decade was also the warmest on record for sea surface temperatures.

The statement added that 'very warm sea surface temperatures contri-buted to the record rainfall and very high humidity across eastern Australia during winter and spring'.

Echoing the scientific panel advising the United Nations on climate change, the Meteorological Bureau-CSIRO assessment for last year said that there was a greater than 90 per cent certainty that an increase in greenhouse gas emissions has caused most of the global warming since the mid-20th century.

If those who believe that man-made global warming gases are intensifying extreme Enso weather are right, the devastation in Australia is a warning that we alter the climate at our peril.

The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.