The increase in air temperature recorded over the past 100+ years has occurred in all seasons and throughout almost all regions of the world. There is also evidence that a more rapid rise in global temperatures that began in the 1970's is continuing and there are indications that the frequency and severity of climate extremes have increased during the past several decades. In this annual summary of the climate of 2008, the NOAA National Climatic Data Center provides an overview of conditions throughout the U.S. and around the world during the past year. As the scientific community works to better understand our changing climate, continual monitoring provides vital information about climate variability and trends, as well as assessing the incidence, impacts and behavior of extreme events. Our primary focus is to give the recent climate record a historical perspective based on more than 125 years of atmospheric measurements as well as paleoclimate records that extend understanding of the Earth's climate to the more distant past. Included is a discussion of century-scale variability and trends in temperature and precipitation, as well as extreme events such as droughts, tornadoes and tropical storms.