Observed changes in the Earth’s climate

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Observed changes in the Earth’s climate

The 1990's appear to be the warmest decade since 1860 and 1998 was the the warmest year. Over the last 1000 years, the 1900's probably saw the greatest temperature increase in the Northern Hemisphere. Less is known about the Southern Hemisphere.


  • Average global temperatures on both the land and the ocean surface have increased by 0.6°C. Temperatures have increased more over land areas than over the oceans.
  • The differences between day and night temperatures have decreased because night temperatures have increased more than day temperatures.
  • The number of hot days has increased.
  • The number of cold days with frost has decreased.
  • The average rainfall in the Northern Hemisphere increased by 5–10% throughout the 1900's. Some areas, such as the Mediterranean region and the northern and western regions of Africa, have had less rain, while other areas have become wetter.
  • The number of extreme rainfall events at mid- and high-latitudes (high latitudes are regions close to the North or South poles) have increased.
  • Areas in Asia and Africa have had more frequent and more intense dry periods during the summer.

Other physical conditions

    • Sea level has increased, on average, by 1 - 2 mm per year during the 1900's.
    • The period when ice covers lakes and rivers became about two weeks shorter per year during the 1900's.
    • Glaciers outside the polar regions have receded.
    • Permafrost (ground or bedrock that is always frozen) in polar and mountain regions has thawed.

drilling into mountain glaciers and ice caps

1. Traces of the past: By drilling deep into mountain glaciers and the ice caps on Antarctica and Greenland, scientists can analyze old ice to find out about the climate in the past. The ice core on the picture contains dust from a volcanic eruption, carried by the wind from far away. Photo: Marzena Kaczmarska/NPI

El Niño is a weather phenomenon in the Pacific Ocean that appears regularly, about every five years around Christmas (which is why it is called “El Niño”, as this means “Baby Jesus”). El Niño has always affected the climate in large areas of the world and led to drought and catastrophic flooding. Scientists believe that global warming may make El Niño more intense and occur more often. This trend has been visible over the last 20 to 30 years.

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About this page:

Author: Camilla Schreiner - CICERO (Centre for International Climate and Environmental Research - Oslo) - Norway.
Scientific reviewers: Andreas Tjernshaugen - CICERO, Norway - 2004-01-20 and Dr. Knut Alfsen - Statistics Norway, Norway - 2003-09-12.
Educational reviewer: Nina Arnesen - Marienlyst School, Oslo, Norway - 2004-03-10.
Last update: 2004-03-27.

Last modified: Friday, 17 May 2019, 4:35 PM