The Pacific Ocean Cloud Feedback
July 25, 2009
One of the most terrifying things about climate change is the potential for massive, abrupt changes brought about by what are called “feedback cycles.” These cycles, not taken into account by the UN’s IPCC in its most recent evaluation of the likely effects of climate change (though those were bad enough) will accelerate the accumulation of greenhouse gases. They are very difficult to quantify, but easy enough to describe, and we are coming to learn more and more about the risks they actually pose.
Feedback cycles include the melting of arctic sea ice, which leads to the exposure of ocean, which is darker than sea ice, and therefore absorbs more energy from sunlight. There is also the possibility of melting in permafrost regions releasing large amounts of carbon from peat bogs and methane reservoirs.
One feedback that has been little remarked upon, however, is the relationship between ocean temperatures and cloud cover.
Some researchers have thought that rising temperatures could lead to greater cloud cover, which might reflect sunlight and moderate temperatures. But a newly published study suggests that – over the northern Pacific at least – rising temperatures actually disspates cloud cover.
Measurements from surface observations were coupled with satellite data to assess the relationship between cloud cover and ocean temperatures over 50 years, producing a dataset which the authors suggest correlates well with some of the more pessimistic climate models.
One of the scientists involved, Amy Clement of the University of Miami, calls this a “vicious circle” – a decent analogy for the feedback mechanisms already identified as contributors to climate change. Added together, these mechanisms pose the threat of rapid, massive and devastating climate change – making immediate action to reduce greenhouse gas emissions imperative.