Scientists say climate change has increased the odds for the kind of weather that prevailed last year.
2011 was one of the 15 warmest years on record. There was severe drought in Texas, droughts in East Africa and unusual heat in England.
The scientists from the United States National Oceanic & Atmospheric Administration and Met Office in Britain have issued an annual State of the Climate report for the 22nd year.
They said the Arctic is warming about twice as fast as the rest of the planet, on average.
Concentrations of carbon dioxide, methane and nitrous oxide continued to rise during the year.