The environment in the news friday, 22 April 2005

Other Environment News

By Jonathan Amos

BBC News science reporter
21 April 2005

A detailed study reported in Science magazine shows nearly 90% of the ice bodies streaming down from the mountains to the ocean are losing mass.

But the authors - a joint team from the British-Antarctic and US-Geological Surveys - say the big melt could have a number of complex causes.

Although higher air temperatures are a factor, they say, the full picture may go beyond just simple global warming.

"The overall picture is of glaciers retreating in a pattern that suggests the most important factor is atmospheric warming; we can connect the retreat with the observed warming recorded at climate stations along the peninsula," explained Dr David Vaughan, from the British Antarctic Survey (Bas).

"But it's not a perfect fit; there seem to be other factors involved as well - possibly to do with changing ocean currents and temperatures," he told BBC News.

The study covers 244 marine glaciers found largely on the western side of the peninsula.

They are all relatively small, independent streams of ice that fall from an altitude of about 2,000m down to sea level. Their fronts either ground and calve icebergs into the ocean, or push out into the water as a floating "tongue".

The team used more than 2,000 aerial photographs dating from 1940, and over 100 satellite images from the 1960s onwards, to assess the change in position of glacier fronts over time.

Bas scientist Alison Cook, who led the research, said: "This is the first comprehensive study of marine glaciers on the Antarctic Peninsula,"

"We found that 87% of the 244 glaciers have shown retreat since the earliest records, which on average were 1953.

"This is a reverse of the pattern 50 years ago - then most glaciers were actually growing. Now the majority are shrinking and rapidly."

The melting trend began in the north of the peninsula and has steadily worked southwards. The last five years have seen the greatest losses in mass, with an average shrinkage of 50m per year.

Some individual losses, however, have been very dramatic. Sjogren Glacier, at the northern end of the peninsula, has moved back 13km since 1993, more than any other glacier in the study.

Sjogren Glacier had flowed into the Prince Gustav Ice Shelf and when the ice shelf broke up in 1993, the glacier retreated rapidly.

Thirty-two glaciers buck the trend, but their advance - an average of 300m per glacier over the study period - is less than the shrinkage of the main group and their distribution fits no clear pattern.

Their growth, the team believes, illustrates the point that glacier length is being influenced by a complex interplay of forces.

The topography, underlying geology, wind and precipitation patterns, the amount of sea ice in front of the glaciers - all could have a role, the researchers say, and at the moment there is little data on any of them.

Computer models

This information will be crucial to the improvement of computer models that are used to predict future climate change in the region, with all the implications that has for further ice melt and possible sea level rises.

These systems have struggled to reproduce the conditions on the Antarctic Peninsula where average air temperatures have risen by around 2C in just 50 years - one of the fastest warming rates on Earth.

Dr Vaughan said: "Whether we can expect that warming trend to extend to the rest of the Antarctic is extremely uncertain.

"The Antarctic is really too small an area to be resolved in the models and that's the level we have to get down to if we want to predict what is going to happen in a particular place."

Dr Andrew Sugden, the international managing editor of Science magazine, commented: "This study demonstrates the enormous importance of gathering long-term data.

"It is only in the accumulation of this data that we are going to be able to understand and predict what might happen to our planet in the future."

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By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - The mercury contained in some vaccines is processed differently in the body and is possibly less toxic to children than mercury found in pollution and fish, U.S. researchers reported on Thursday.

Tests in monkeys showed that the ethyl mercury contained in the vaccine preservative thimerosal is cleared quickly by the body, while methyl mercury persists much longer.

This suggests that current Environmental Protection Agency guidelines on mercury exposure should not apply to the type of mercury in vaccines -- and could help answer doubts about the safety of some vaccines, the researchers wrote in this week's issue of Environmental Health Perspectives.

"The current debate linking the use of thimerosal in vaccines to autism and other developmental disorders has led many families to question whether the potential risks associated with early childhood immunizations may outweigh the benefits," Thomas Burbacher of the University of Washington in Seattle and colleagues wrote in their report.

The Institute of Medicine, an independent body that advises the federal government, has said there is no evidence of any link between vaccines and autism. It has advised researchers looking for the causes of autism to look elsewhere.

This has enraged autism activists, who fear a cover-up.

Burbacher's team said it would make sense to study more closely the effects of thimerosal, a mercury-based preservative once widely used in vaccines. It has been removed from most childhood vaccines because of the furor.

Thimerosal remains in the influenza vaccine and in some vaccines used outside the United States.

Current government advice on vaccine exposure limits are based on studies done on people who were exposed to methyl mercury from industrial accidents. It can clearly cause long-term brain and nervous system damage.

An earlier study calculated that children receive 187.5 micrograms of ethyl mercury from thimerosal-containing vaccines given over the first 14 weeks of life. This can exceed EPA guidelines for methyl mercury exposure during pregnancy.

Some experts have argued that thimerosal breaks down into a different form of mercury in the body -- ethyl mercury -- and that this is cleared more quickly.

Tests on human infants suggest this does happen, but their brains cannot be directly examined.

Burbacher's team tested 41 newborn monkeys, feeding them either methyl mercury or giving them shots of thimerosal in doses comparable to those given vaccinated human infants. The mercury from the vaccines was cleared out of the body much more quickly than was methyl mercury, they said.

It took just over eight days to completely clear mercury from thimerosal, while it took 21 days to clear methyl mercury from the blood, they found.

"Brain concentrations of total mercury were significantly lower by about three-fold for the thimerosal-exposed infants when compared to the methyl mercury infants," they wrote.

The researchers said this does not mean thimerosal is harmless and urged more research.

"This information is critical if we are to respond to public concerns regarding the safety of childhood immunizations," they wrote.

"This study emphasizes that thimerosal and methyl mercury behave differently in the body. Given that we routinely inject thimerosal into millions of infants, the study authors' call for more in-depth research on the subject is the right way to go," said Dr. Jim Burkhart, science editor for the journal.