Guest essay by Eric Worrall
Two new studies have promoted concerns that anthropogenic global warming could cause abrupt cooling in the Northern Hemisphere – the “Day after Tomorrow” scenario.
According to the Sydney Morning Herald;
Two new studies are adding to concerns about one of the most troubling scenarios for future climate change: the possibility that global warming could slow or shut down the Atlantic’s great ocean circulation systems, with dramatic implications for North America and Europe.
The research, by separate teams of scientists, bolsters predictions of disruptions to global ocean currents – such as the Gulf Stream – that transfer tropical warmth from the equator to northern latitudes, as well as a larger conveyor system that cycles colder water into the ocean’s depths. Both systems help ensure relatively mild conditions in parts of Northern Europe that would otherwise be much colder.
Climate change can influence sea surface conditions and the melting rates of ice sheets; resulting in decreased deep water formation rates and ultimately affecting the strength of the Atlantic Meridional Overturning Circulation (AMOC). As such, a detailed study of the interactive role of dynamic ice sheets on the AMOC and therefore on global climate is required. We utilize a climate model in combination with a dynamic ice sheet model to investigate changes to the AMOC and North Atlantic climate in response to Intergovernmental Panel on Climate Change scenarios for RCP4.5 and RCP6. It is demonstrated that the inclusion of an ice sheet component results in a drastic freshening of the North Atlantic by up to 2 practical salinity units, enhancing high-latitude haloclines and weakening the AMOC by up to 2 sverdrup (106 m3/s). Incorporating a bidirectionally coupled dynamic ice sheet results in relatively reduced warming over Europe due to the associated decrease in heat transport.
Proxy records of temperature from the Atlantic clearly show that the Younger Dryas was an abrupt climate change event during the last deglaciation, but records of hydroclimate are underutilized in defining the event. Here we combine a new hydroclimate record from Palawan, Philippines, in the tropical Pacific, with previously published records to highlight a difference between hydroclimate and temperature responses to the Younger Dryas. Although the onset and termination are synchronous across the records, tropical hydroclimate changes are more gradual (>100 years) than the abrupt (10–100 years) temperature changes in the northern Atlantic Ocean. The abrupt recovery of Greenland temperatures likely reflects changes in regional sea ice extent. Proxy data and transient climate model simulations support the hypothesis that freshwater forced a reduction in the Atlantic meridional overturning circulation, thereby causing the Younger Dryas. However, changes in ocean overturning may not produce the same effects globally as in Greenland.
Northern deep freeze studies seem to be fashionable lately, even Michael Mann had a go earlier this year.
Perhaps giant blocks of ice washing up on American beaches is proving difficult to reconcile with the end of snow narrative. Having said that, there has always been a low profile nod towards the possibility of abrupt cooling, which is of course still all our fault. This apparent effort to keep all the options open is beautifully captured by one of my favourite climategate emails.
Climategate email 4141.txt (written in 2004)
In my experience, global warming freezing is already a bit of a public relations problem with the media, which can become public perception. It provides a new story for the old news that is climate change – a story that has been running since 1985/88.
Last Friday, even NERC put-out a press release that opened ‘British scientists set sail today from Glasgow to begin work aimed at discovering if Britain is indeed in danger of entering the next ice age.’
Dear Asher, and all,
I think this is a real problem, and I agree with Nick that climate change might be a better labelling than global warming. But somehow I also feel that one needs to add the dimension of the earth system, and the fact that human beings for the first time ever are able to impact on that system.
Let’s not forget folks, that what we are dealing with is “settled science”.