The world is now entering a critical era in which a tipping point could arise beyond which human beings will lose the ability to stop runaway global warming.
What are the feedback processes that cause accelerated warming?
First it is necessary to understand that the build up of greenhouse gases can create feedback mechanisms – some with warming and others with cooling – effects. The important point to bear in mind is that the warming effects outweigh the cooling ones. As the quantity of greenhouse gases builds up in the atmosphere this causes effects that increase the warming. The warming itself causes effects which increasethe warming still further. The main effects are summarised below:
Rising CO2 will cause acidification in the oceans killing
plankton which sequesters carbon dioxide thus increasing CO2
concentration in the atmosphere.
Vast stores of methane (a greenhouse gas 24 times more potent than CO2) are trapped or ‘frozen’ in crystal lattice form in sea bed deposits. Rising temperatures in the oceans would release methane into the atmosphere. Methane will gradually break down into CO2 and water vapour, but CO2 has an atmospheric life measured in centuries or even millennia.
Methane is also trapped in large expanses of frozen tundra and this would be released with thawing.
As temperatures rise, the concentration of water vapour in the atmosphere rises. Water vapour is itself a very powerful
greenhouse gas. So this is also a strong and rapid feedback
Increased water vapour would also cause cloud formations that have both warming and cooling effects, the overall impact of
which is uncertain. However, warmer cloud systems would
increase the energy and impact of storm events.
The effect of melting ice would be to replace a white shiny
surface which reflects heat back into space with a dark surface
Human activities, including deforestation, present farming practices which break down soil carbon and convert it to CO2 and involve large amounts of fossil fuels, industrial processes and transport using fossil fuels, have already raised the carbon dioxide concentration in the atmosphere above the level which scientists believe will cause catastrophic climate changes. This is above the level that would make a 2˚C temperature rise causing such changes, inevitable. The recorded level of CO2e (carbon dioxide equivalent) in 2006 has been measured at 420 ppm and the rate of accumulation (now at 2 ppm per year) is
accelerating. Hence the feedback dynamics outlined above indicate that not only is it an urgent necessity to stop the use of fossil fuels, but also to adopt measures that would remove CO2 from the atmosphere.