I've looked it up on their website - 9 Feb 2006:

"WHEN the Indonesian volcano Krakatoa erupted in 1883, sending 25 cubic
kilometres of rock and ash into the air, it did more than generate the
loudest sound ever recorded. It also cooled the world's oceans and
suppressed rises in sea level for decades afterwards.

"Peter Gleckler of the Lawrence Livermore National Laboratory in
California and colleagues compared climate models that included
volcanoes with those that did not. To their surprise they found that
volcanoes seem to have a cooling effect on the oceans that lasts for up
to a century after an eruption. The cooling effect of Krakatoa lasted
well into the 20th century, says Gleckler.

"Big volcanoes inject ash high into the atmosphere and block out
sunlight for months or even years, which cools ocean surface waters
(Nature, vol 439, p 675).

"However, global warming appears to have diminished this long-term
effect, he says."

I'm not into global warming denial, just wondering how much effect in
the 20th century was down to starting from a Krakatoa induced low
point. And I was also trying to remember when the last major volcano
blew its top - was it Mt St Helens?