Summary of Global Warming Observations

  • Rate and duration of warming in 20th century is larger than any other time in last 1000 years.
  • The 1990s are likely to have been warmest decade of the millennium in the Northern Hemisphere.
  • 1998 is likely to have been the warmest year.
  • Note:  A few areas of the globe have not warmed in recent decades:  some areas of Southern Hemisphere and parts of Antarctica
  • Total atmospheric water vapor has likely increased several percent per decade over many regions in NH
  • some subtropical regions are experiencing more dry spells
  • Annual land precipitation has increased in the middle and high latitudes of the Northern Hemisphere.
  • Increased cloud cover by about 2% since the beginning of the 20th century over the Northern Hemisphere.
  • Decreasing snow cover and sea-ice amounts in NH.  No significant trends in Antarctic sea-ice are apparent.
  • Global mean sea-level rise during 20th century has been observed to be 1.0-2.0 mm per year.
  • Increase in heavy and extreme precipitation events in regions where total precipitation has increased. 
table from 4th IPCC Assessment