Climate Change ‘positive feedbacks’ are the effects of climate change that feed back into the climate system and reinforce the severity, speed and impact of global warming.
The strength of positive feedbacks is very difficult to predict. For this reason, many positive feedbacks were omitted from the most recent IPCC report, which limited itself to predictions based on definite scientific findings.
Instead, impacts were generally plotted at a ‘linear’ rate of change, i.e. a straight line graph.
In the real world, predominantly positive feedbacks tend to produce an accelerating curve, rather than a straight line.
This is one reason why, in official predictions, the pace of climate change tends to be dangerously underestimated.
Examples of positive feedbacks include:
- Increased evaporation from the oceans. Water vapour is in itself a powerful greenhouse gas. As climate change causes the oceans warm, more water evaporates, contributing to the greenhouse effect, and causing further evaporation.
- Loss of sea ice and snow cover. White surfaces reflect more of the Sun’s rays. So as global warming melts ice and snow, this reduces the reflectivity of the polar regions, and results in more heat being absorbed.
- Loss of forests. As forests dry out they die off and are more susceptible to disease and forest fires, releasing more Co2 into the atmosphere, and contributing to the greenhouse effect, which warms forests even more. Droughts in the Amazon rainforest demonstrate that the Earth’s forests are already nearing a tipping point that could result in 80% of the forest dying off and releasing its carbon reserves into the atmosphere.
- Permafrost melting. As the northern permafrost thaws, greenhouse gases such as Co2 and methane are released from the swampy ground, contributing to more global warming.
Negative feedbacks are effects of global warming which slow the problem. It was thought that increased cloud cover might be an example of negative feedback but unfortunately the most recent research shows that the commonest clouds, formed over ocean, have a net positive effect, increasing the amount of warming.
Any system with predominantly positive feedbacks will show accelerating change towards some tipping point. One common example is childbirth where the descent of the baby creates more and more powerful contractions of the womb, until the final tipping point which is the moment of birth.
Doctors trying to prevent premature deliveries know that the further one progresses towards the final event (birth), the harder it is to halt or delay the progress of labour.
The same applies to climate change. the longer we delay preventive solutions, the more certain we are to face some final cataclysmic outcome which is entirely beyond our control.
John Collee, ‘The Mammoth in the Freezer’, The Sydney Morning Herald, 6 June 2009, http://www.smh.com.au/environment/climate-change/the-mammoth-in-the-freezer-20090605-byhl.html
James Hansen, ‘Scientific reticence and sea level rise’, Environmental Research Letters, 24 March 2007, http://www.iop.org/EJ/article/1748-9326/2/2/024002/erl7_2_024002.pdf?request-id=064f8e5f-b85f-4260-843a-3f82ed02d496
Leo Murray, ‘Wake Up, Freak Out, Get a Grip’, www.vimeo.com/1709110?pg=embed&sec=1709110
Skeptical Science, 2009, ’The Albedo Effect’, http://www.skepticalscience.com/the-albedo-effect.html.
Ian Ammison, et. al., ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, 2011, p. 58.
K M Walter, et. al, 2006, ‘Methane Bubbling from Siberian Thaw Lakes as a Positive Contribution to Climate Change’, Nature, 443(7), http://faculty.jsd.claremont.edu/emorhardt/159/pdfs/2007/Walter%20et%20al.%202006.pdf.
National Snow and Ice Data Centre, ‘Arctic Climatology and Meteorology’, http://nsidc.org/arcticmet/patterns/feedback_loops.html