The World Meteorological Organization says last year was one of the warmest on record, in a report to the United Nations.

The WMO tracks the weather on behalf of the 193 countries of the United Nations. In the report, unusual and extreme weather events, such as Superstorm Sandy in the U.S. and Typhoon Bopha in the Philippines, were linked to climate change.

"Although the rate of warming varies from year to year due to natural variability caused by the El Niño cycle, volcanic eruptions and other phenomena, the sustained warming of the lower atmosphere is a worrisome sign. The continued upward trend in atmospheric concentrations of greenhouse gases and the consequent increased radiative forcing of the Earth's atmosphere confirm that the warming will continue," said WMO Secretary-General Michel Jarraud in a news release.

The report also stated that the Arctic sea ice extent was recorded at its lowest ever last year. The extent of the ice at the end of the annual melt last year dropped to 1.32 million square miles. Arctic sea ice extent is measured by the amount of ice in summer. It is seen as a key player in Earth's climate system and one whose decline is widely taken as a prominent sign of global warming.

"The record loss of Arctic sea ice in August-September — 18 percent less than the previous record low of 2007 of 4.17 million km2 — was also a disturbing sign of climate change. The year 2012 saw many other extremes as well, such as droughts and tropical cyclones. Natural climate variability has always resulted in such extremes, but the physical characteristics of extreme weather and climate events are being increasingly shaped by climate change," Jarraud added.

Last year was the 27th consecutive year that showed an above-average global temperature. The years between 2001 and 2012 are among the top 13 warmest on record.