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Observed changes in concentrations of greenhouse gases in the atmosphere

• Carbon dioxide (CO₂) has increased from 280 ppm (280 litres of CO₂ in a million litres of air) in the period 1000 to 1750 to about 370 ppm today. This is about a 31% increase and today’s levels are the highest atmospheric CO₂ concentrations in at least 420,000 years, probably 20 million years.
• Methane (CH₄) has increased from 0.7 ppm in 1750 to 1.7 ppm in 2000. This is an increase of about 151%.

1. Increase in greenhouse gas concentrations (in ppm) from 1750 to 2000. Graphics: Elmar Uherek

• Nitrous oxide (N₂O) has increased from 0.27 ppm in 1750 to 0.32 ppm in 2000. This is about a 17% increase.
• Tropospheric ozone (O₃) has increased by about 35% from 1750 to 2000. This figure, does however, vary from region to region. Ozone in the lower atmosphere is a greenhouse gas, it is formed and broken down by chemical reactions in the atmosphere, and humans emit other substances which influence these chemical reactions.

(Source: IPCC 2001 and http://cdiac.esd.ornl.gov/pns/current_ghg.html).

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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.