The Northern Hemisphere is warmer than it has been at any time in the last 1,200 years, according to a new study.

The findings support growing evidence of wide-scale global warming as a result of increased greenhouse emissions.

University of East Anglia researchers measured changes in fossil shells, ice cores, tree rings and temperature records.

They analysed thermometer measurements of temperature from 1856 onwards and compared it with evidence dating back as far as AD 800.

The study showed significant warmth in the Northern Hemisphere from AD 890-1170 and much colder periods from 1580-1850.

Co-author Timothy Osborn said: "The 20th century stands out as having unusually widespread warmth, compared to all of the natural warming and cooling episodes during the past 1,200 years."

Osborn and Keith Briffa gathered climate change data from 14 sites across North America, Europe and Asia.

The data included long life evergreen trees growing in Scandinavia, Siberia and the Rockies, which had been cored to reveal the patterns of wide and narrow tree rings over time. Wider rings related to warmer temperatures.

They also used a record developed from diaries of people living in the Netherlands and Belgium to find out when canals in that area had frozen over.

The study findings are published in the journal Science.