A new study by climate scientists behind the controversial 1998 "hockey stick" graph suggests their earlier analysis was broadly correct.

Michael Mann's team analysed data for the last 2,000 years, and concluded that Northern Hemisphere temperatures now are "anomalously warm". Different analytical methods give the same result, they report in Proceedings of the National Academy of Sciences.

The 1998 hockey stick was a totem of debates over man-made global warming. The graph - indicating that Northern Hemisphere temperatures had been roughly constant for 1,000 years (the "shaft" of the stick) before turning abruptly upwards in the industrial age - featured prominently in the Intergovernmental on Climate Change's (IPCC) 2001 assessment. But some academics questioned its methodology and conclusions, and increasingly strident condemnations reverberated around the blogosphere.

One US politician demanded to see financial and research records from the scientists involved. However, a 2006 report from the National Research Council (NRC), commissioned by the US Congress, broadly endorsed its conclusion that Northern Hemisphere temperatures in the late 20th Century were probably warmer than at any time in the previous 400 years, and perhaps at any time during the previous 1,000 years.