Pollution is not the reason of temperature drop in Northern Hemisphere around 1970

The new research, led by Dave Thompson from Colorado State University in Fort Collins, US, shows that the top layers of Northern Hemisphere water cooled by about 0.3C between 1968 and 1972, while the South Hemisphere saw approximately the same degree of warming.

But the timescale of the drop is much shorter, than that previously linked to the increasing sulphate aerosols from fossil fuel in the troposphere, or changes in the climate of the world’s oceans that evolve over decades (oscillatory multidecadal variability).

Photo: ijolumoet.com

This research suggests that the explanation of the cooling could lie somewhere else, it is not clear where, since the effect of aerosols is expected to be more gradually.

A model developed by Thompson which uses data collected by ships and buoys over the past two and a half centuries examined temperature change on a month-by-month basis, unlike previous studies that look at temperature change on a decadal scale.

The team fed the data into a model that blocks out short-term changes in ocean temperature – triggered, for example, by volcanic eruptions which spew sulphur aerosols into the atmosphere. This allowed them to identify changes in ocean temperature that weren't linked to natural variation; The Guardian wrote on 22 September 2010.

It is unclear what caused the cooling process, but an unusually large discharge of ice from the Arctic Ocean in 1967 is the reason of a 10,000 cubic kilometre pool of fresh water from the coast of Greenland, which appears to have lowered the salinity of water in the North Atlantic, according to Mark Maslin of the Environment Institute at University College London.

One possibility is the Great Salinity Anomaly (GSA) which presumably interrupted the mixing process of cooled surface water and warm deep water that caused a cool period by dumping light, fresh water on the surface.

Still, it is a fact that currently greenhouse gases are warming up the Planet.


Written by Jasmina Nikoloska
Sources: Abstract of the paper in Journal Nature

               The Guardian