Carbon dioxide ppm levels and targets

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Level of carbon dioxide in the world's atmosphere, expressed as parts per million (ppm), have been the subject of significant scientific research and modelling to better understand the effects of climate change and make predictions for future trends.

Some notable levels are:

Level (ppm) Observations
280 Pre industrial level
380 2008 level, considered likely to result in a 2C global temperature rise
450 Level suggested for international negotiations, but considered dangerous due to likely 3C global temperature rise
550 Considered very dangerous due to likely global temperature rise above 3C
650 Level predicted for 2050 based on current carbon emissions. Considered extremely dangerous.

Rate of CO2 level increase

Scientists at the Mauna Loa observatory in Hawaii say that CO2 levels in the atmosphere now stand at 387 parts per million (ppm), up almost 40% since the industrial revolution and the highest for at least the last 650,000 years.

The figures, published by the US National Oceanic and Atmospheric Administration (NOAA) on its website, also confirm that carbon dioxide, the chief greenhouse gas, is accumulating in the atmosphere faster than expected. The annual mean growth rate for 2007 was 2.14ppm – the fourth year in the past six to see an annual rise greater than 2ppm. From 1970 to 2000, the concentration rose by about 1.5ppm each year, but since 2000 the annual rise has leapt to an average 2.1ppm." [1]

550ppm CO2 equates to dangerous climate change

A major conclusion arising from the study of the recent history of the atmosphere is that carbon cycle feedbacks coupled with ice melt/water feedbacks constitute major amplifying mechanisms of initial relatively minor solar and greenhouse triggers (forcings). This observation is central to the view of the acceptability, or otherwise, of a 550 ppm CO2 atmosphere, for the following reasons:

  1. Based on a climate sensitivity of 3 degrees for a doubling of atmospheric CO2 levels, at 550 ppm CO2 which is twice the pre-industrial level of 280 ppm CO2, mean global temperatures will rise to about 3 degrees Celsius
  2. A rise of global temperature of 3 degrees Celsius implies sea level rise of about 25 metres +/- 12 metres, as recorded from the mid-Pliocene (3 million years ago) and consistent with sea level rise/temperature relations during glacial terminations
  3. Temperature rises to 3 degrees Celsius imply widespread desertification of mid-latitudes the agricultural centres of the world
  4. Natural sequestration of greenhouse gases occurs over time frames of centuries to millennia and no atmospheric mechanism is known which will stabilize CO2 levels over shorter periods
  5. In terms of the longevity of civilization, allowing CO2 levels to rise further than they already are (387 ppm) would prove to be a unidirectional process[2]


  1. World CO2 levels at record high, scientists warn,, May 12, 2008
  2. A target of 550 ppm CO2 is a recipe for disaster,, October 1, 2008
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