I'm not a big fan of alarmist news on scientific research as the PR and
even the theories or conclusions themselves are inevitably based on a
false premise. However there is an interesting article in this weeks
Earth Observatory's newsletter:

http://earthobservatory.nasa.gov/Stu...hreshold2.html

also the want readers to vote for them in some sort of popularity
contest if you find their stuff interesting or useful:

http://peoplesvoice.webbyawards.com/login.mhtml
(Appreciative as I am of their efforts, you have to register to vote
and the people running the site are Verizone of all people. They are
the URL hijackers with privateer licenses from the US government.)

Back to the article:

Goetz analysed satellite imagery of the Northern forests of North
America. He had wanted to know how the forests use carbon dioxide as
they recover from fire so he could determine the impact of fire on the
carbon cycle.

As Goetz expected, the satellite data showed that the newly burned
forest was "greening up" as it recovered to pre-burn conditions.
But in the surrounding unburned forest, growth was slowing down, and
that surprised Goetz. "Earlier work suggested greening in the
Northern Hemisphere and an increase in the growing-season length,".

But why were the forests in decline?

Scientists have always thought that plant growth in the boreal forests
was limited by temperature. Arctic summer provides a brief period in
which plants can thrive before the cold of winter ends the growing
season.

If temperatures had extended the growing season, plants should have
grown more. But Goetz and his colleagues suspected that warmer
temperatures had also dried the forest.

"Most people wouldn't think of these boreal forests as being
drought stressed,"

they weren't certain that dryness was the only thing affecting the
trees. It was possible that other factors, such as nutrient stress or
insect damage, could be to blame. Strong evidence that drought was
really to blame would come from a second source.

Here we go:
But then, in 1991, Mount Pinatubo erupted, sending a cloud of sulfate
aerosols into the upper atmosphere.

I am a pedant I know but when responsible organisations insist that
volcanic ash contains sulphuric acid...

Or are they talking about calcium sulphate?

I wonder if the prevalence of organic or fossil residue sulphur in
volcanoes is anything to do with the way thy erupt. Suppose that deep
under the sulphur beds there are huge wells of oil and methane from all
the big lizards that died there to produce the sulphur...