One in 20 Year Events as Climate Shifts with Rising Sea Temperatures

OneĀ in 20 Year Events as Climate Shifts with Rising Sea TemperaturesĀ 

There’s a growing risk that events of this type (floods in Australia, Brazil and Sri Lanka) will become more frequent as the climate warms, says Prof Will Steffen says. What were one-in-100-year events would become a one-in-20 or one-in-30-year event as the climate shifts. While Michael Richardson points out that 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.

NZ Herald (13 January 2011):

Experts blame a combination of a La Nina weather pattern and global warming for the magnitude of the Queensland flood disaster.

One scientist warns the catastrophe is only the start of things to come, saying what are described now as one-in-100-year floods could arrive every 20 years.

The La Nina effect, the inverse of the drought-inducing El Nino effect, results in higher than average sea temperatures in the Pacific Ocean leading to heavy rain.

Professor Will Steffen, executive director of the Australian National University’s (ANU) Climate Change Institute, says it is likely the floods are climate change related.

“What we can say about the Queensland floods is there is a strong La Nina, which tends to give this heavy rainfall, but in addition to that there are very high sea surface temperatures.”

Professor Matthew England, joint director of the Climate Change Research Centre at the University of NSW, says the temperatures are the highest ever recorded.

Rising sea temperatures, especially in northern Australia, are a key part of the climate system, says Prof England.

“Climate change has seen a warming of waters globally, and the waters north of Australia are an important part of the climate system for Australia’s monsoon rains.

“They are at their warmest ever measured and we cannot exclude climate change from contributing to this warmth, (and) if it is very warm there this enhances evaporation into the atmosphere, creating moist air.”

Prof Steffen agrees the temperature rise is a climate change phenomenon.

Sea temperatures have been rising for years, he says.

He cites a study in the US that looks at rainfall in a heavily saturated area over the past 100 years.

“(In the study) there’s been a significant increase (in rain in the area) since 1980 consistent with a strong warming,” Prof Steffen says.

The study shows the the effects of warming will make flooding of the type that has devastated parts of Queensland more common.

“There’s definitely a risk and a growing risk that events of this type will become more frequent as the climate warms,” Prof Steffen says.

“One-in-100-year events would become a one-in-20 or one-in-30-year event as the climate shifts … we say with some confidence they are becoming more frequent and they will become more frequent in future.”

Prof England says that climate change projections point to extreme weather becoming more common, but it is hard to know how much flooding Australia could get.

“Climate change projections are pointing to more frequent extreme events, that’s to say more flooding events, more droughts and fires, but whether Australia as a nation sees many more flooding events or not is still a little bit more complex to pin down,” he says.

But not all experts agree that global warming is a factor.

Environmental science Professor Neville Nicholls from Monash University believes the Queensland floods are not due to climate change but purely a result of La Nina.

“The main reason we’re seeing this heavy rain is just this incredibly strong La Nina, and that’s almost certainly a natural part of climate variability,” he says.

Prof Nicholls says the evidence is inconclusive about the effect of global warming on the La Nina phenomenon.

“The question is, is it exacerbated by climate change or global warming? At the moment, we just can’t say. No one has done the studies yet,” he says.

“You would have to think the warming we’ve seen – about half a degree in the last 30 or 40 years – should have had some influence on this event, but we can’t tell you reliably or credibly what that influence is.”


Michael Richardson for the Straits Times (17 January 2011):

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.


Leave a Reply