( CNN ) -- The first decade of the 21st century was the warmest ever on Earth according to data released by scientists at NASA . The U.S. space agency 's data also revealed that 2009 was the second warmest year since temperature records began in 1880 , and only narrowly cooler than 2005 , the warmest year ever . 2008 was the coolest year of the decade but this was attributed to a strong La Nina which causes extensive cooling of the central and eastern Pacific Ocean . James Hansen , director of NASA 's Goddard Institute for Space Studies ( GISS ) said in a statement : `` There 's substantial year-to-year variability of global temperature caused by the tropical El Nino-La Nina cycle . When we average temperature over five or ten years to minimize that variability , we find global warming is continuing unabated . '' In the past three decades , GISS report surface temperature records show an upward trend of about 0.2 degrees Celsius ( 0.36 degrees Fahrenheit ) per decade . In total , according to GISS , average global temperatures have increased by about 0.8 degrees Celsius ( 1.5 degrees Fahrenheit ) since 1880 . GISS sources its data using over one thousand weather stations around the world , satellite observations of sea surface temperatures , and research station data from Antarctica -- all of which , they say , is readily available to the public .
2000 to 2004 was the warmest decade since records began . 2006 was warmest year of all time , 2008 coolest in decade . Global temperatures have averaged 0.8 degrees C since 1880 .