Lead paragraphs from the BBC story:
"Unusually warm and cold periods in Earth's pre-industrial climate history are linked to how the oceans responded to temperature changes, say scientists.
The researchers focused particularly on intervals known as the "little ice age" and "medieval warm period".
In the journal Science, they report that these climate "anomalies" were likely caused by changes to El Nino and the North Atlantic Oscillation."
This story, interesting in itself, gained an addition dimension for me when I recognised the name of the lead researcher, Michael Mann. Professor Mann (as climate mavens will know) was one of the researchers named in the emails recently hacked and publicised on the Web. (These emails are being represented as evidence of a conspiracy to stifle dissent in climate research - see the NYT story here.)