Friday, March 11, 2011

Carbon dioxide in the atmosphere matters

Sunlight reaching our planet is dominantly a short-wavelength energy, which passes easily through our atmosphere to warm the surface of the planet. As the surface warms, it emits an increasing amount of infrared, or long-wavelength, energy back out into the atmosphere: the incoming short-wavelength energy has been converted into outgoing long-wavelength energy.

Molecules made up of two atoms of the same element, such as nitrogen (N2) or oxygen (O2), have no net change in their dipole moment when they vibrate and so do not absorb infrared energy, but 3-atom (or more) molecules, such as carbon dioxide (CO2), do. Consequently nitrogen and oxygen are not greenhouse gases as the infrared energy emitted from the planet surface would easily pass back out through an atmosphere of these gases.

By contrast, carbon dioxide does absorb the outgoing infrared energy, gradually accumulating more heat and increasing the temperature of the planet’s surface. The greater the concentration of carbon dioxide, the more the temperature increases.

It is well-known that the greenhouse effect of the carbon dioxide currently in our atmosphere is about 33°C. In other words, the planet surface is about 33°C warmer than it would be without the greenhouse effect. As it stands, this is enormously beneficial to us, for a planet 33°C cooler than now would not be habitable by humans.

However, the converse is also true. A planet substantially warmer than now would not be habitable by humans either. Consequently, fundamental questions for us as a species are whether our activity is actually capable of increasing the carbon dioxide concentration significantly and how much any such increase is liable to increase the temperature.

Monday, February 21, 2011

Global carbon emissions to double

The recently published Global Emissions Trends analysis projects that in a "business as usual" scenario (i.e. no changes to carbon emission policies) global carbon emissions will double by 2030.

This would make the IPCC target of a 50% reduction in global carbon emissions by 2050 (on 1990 levels) difficult to achieve, increasing the probability of global mean temperatures rising above the critical level of +2 Degrees. (See why 2 Degrees is a critical level in The 2 Degree Target).

Under this scenario:
  • Developing countries will account for 70 per cent of global carbon dioxide by 2030, up from around half today, with China (41%) and India (11%) taking the largest share, due to increasing population (+22% by 2030), industrialisation, and the greater energy demands as living standards improve in these countries.
  • Australia's carbon emissions would rise 24% by 2020. The strong growth in emissions would be dominated by the extraction and processing of energy resources.
This disastrous scenario will not happen if governments shape public policy to transition towards a low-carbon future. This research forms part of eight papers in the Garnaut Climate Change Review - Update 2011.