Every year since 1990, the National Oceanic and Atmospheric Administration has released an annual report detailing the state of the climate. Early versions were typewritten and authored by a handful of experts. The new version is a shiny, 218-page PDF penned by more than 300 scientists from around the world. Nevertheless, the message has changed little over the years: the world is warming.

The 2009 report continues to document a number of weather-related records, the number of which seem to be growing every year. This year's highlights: The hottest decade on record. The third-lowest Arctic sea ice extent since 1979. The warmest and second-warmest years on record for India and Australia, respectively. And carbon dioxide concentrations that are increasing at a rate well above average.

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Also notable in the 2009 report is the amount of space dedicated to explaining the methods and data behind the sections on climate change. A two-page sidebar in the chapter on global surface temperatures (“How we know the world has warmed?” in chapter two [PDF]) details three major climate models for the layperson. The authors even constructed interactive figures—complete with links to the original data—so anyone can probe the data for themselves.

“Despite the variability caused by short-term changes, the analysis conducted for this report illustrates why we are so confident the world is warming,” Peter Stott, head of Climate Monitoring and Attribution at the Hadley Met Office, said in a statement. “When we follow decade-to-decade trends using multiple data sets and independent analyses from around the world, we see clear and unmistakable signs of a warming world.”

Global average surface temperatures have risen 0.2°C above the 1990s average and 0.3°C above the 1980s average. Those values are large given the short time span, but seem mild considering that the report estimates 90 percent of the warming over the past 50 years has been absorbed by the oceans.

The polar regions are again proving especially vulnerable to the warming climate. Arctic sea ice extents have been reaching repeated record minimums. And while the Antarctic sea ice was near normal levels this year, the Antarctic Peninsula has been warming at a rate five times the global average. Boreal ecosystems have been hit hard with rising permafrost temperatures and lengthening green seasons, or the time between plant green-up and senescence.

Glaciers—another climate change victim—continued their global retreat. Preliminary data suggests 2009 will have been the 19th consecutive year where more glacier ice was lost than was gained. Greenland’s glaciers that spill into the sea lost 101 square kilometers of ice, pushing total losses over 1,000 square kilometers for the decade.

The authors of the report drew on 37 different variables—seven more than just two years ago—ranging from air temperature to seawater carbon dioxide levels to subsurface ocean currents. Ten of these received in-depth commentary and analysis.

The report also details the finer climate patterns that help explain year-to-year variations. The previous years’ La Niña disappeared, replaced by an intensifying El Niño. Sea surface temperatures began noticeably rising in June 2009 and were 2°C warmer by December. This transition, the authors note, is largely responsible for the decreased hurricane and cyclone activity in 2009. The report does not include any weather data from this year, which NOAA points out is on track to be the hottest ever recorded.

Listing image by Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC