Insect deaths add to extinction fears British survey
hints that species are crashing worldwide. 19 March 2004
MICHAEL HOPKIN
Ecologists have unveiled strong evidence that huge numbers
of the world's species are disappearing. A survey of British
wildlife suggests that insects - thought to be among the
most resilient species - are suffering similar extinction
rates to larger, better-studied animals.
If the same is happening worldwide, we may be witnessing
the largest die-off since the mass extinction that killed
the dinosaurs, says Jeremy Thomas of the Centre for Ecology
and Hydrology in Dorset, UK, who led the study in this
week's Science1.
Thomas's team analysed surveys of British birds, plants and
butterflies stretching back 40 years. The statistics,
collected by 20,000 amateur naturalists, form an
unprecedented census of insects. "No dataset approaches this
detail and scale anywhere in the world," Thomas says.
The researchers divided Britain into 10-kilometre squares
and counted the number of squares occupied by each species.
Of 58 butterfly species, 71% have declined or disappeared
over the past 20 years, alongside 54% of birds. The past 40
years has seen declines in 28% of plants studied.
Experts had assumed that the sheer number of insects
would safeguard them against mass extinction. "The gloomy
result is that this group has declined massively," says
Thomas. As insects comprise more than 50% of the planet's
species, a large die-off would be bad news for global
diversity, he adds.
Read the rest at Nature nature.com040315Open ↗
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Did cracking continent trigger a deep freeze? The break-up
of a supercontinent may have caused a 'Snowball Earth'. 18
March 2004 PHILIP BALL
The Earth might have been sent into an ice age by the break-
up of a supercontinent 750 million years ago, creating a
global snowball.
The break-up probably caused an increase in rainfall and
weathering of rock, say climatologists. This would have
sucked greenhouse gases out of the atmosphere and caused a
run-away cooling effect. The mechanism could explain how the
entire planet becomes encased in a mass of ice, as many
researchers think it has done in the past.
The theory that the Earth was once completely frozen emerged
in the 1960s, when scientists realised that global freezing
could happen if the polar ice sheets grew above a certain
threshold size. Because bright ice reflects sunlight and
heat back into space, growing ice sheets cause further
cooling. This feedback loop could tip the climate system
into a deep freeze.
The planet could eventually thaw as carbon dioxide from
volcanoes poking through the ice warm it.
In the late 1980s, Joe Kirschvink of the California
Institute of Technology nicknamed this state 'Snowball
Earth'. Around the same time, geologists began to uncover
hints in the geological record that this freeze-thaw
process might have happened at least once in the distant
past - at the end of the Proterozoic eon, 600 to 800
million years ago.
But it was unclear what could have tipped the world into
that state in the first place. Now Yannick Donnadieu of the
Laboratoire des Sciences du Climat et de l'Environnement in
Gif sur Yvette, France, and co-workers provide an
explanation in this week's Nature1.
Posted by Robert Karl Stonjek.