The polar regions are the fastest warming regions on our planet. Look at any global map of the way the world has warmed recently and you will see that the reddest regions found anywhere are above Canada and around a bit, and in the Antarctic peninsula.
It is, of course, understandable and indeed predictable. Climate models predict that it will be the polar regions that should the first signs of global warming due to the accumulation of greenhouse gasses.
According to the IPCC this is because “ice has greater reflectivity than the ocean or land. Melting of highly reflective snow and ice reveals darker land and ocean surfaces, increasing the absorption of the sun’s heat and causing further warming. There is evidence that climate change is already having observable impacts in the Arctic and in Antarctica. Many of these observed changes are consistent with the expected effects of climate change under a range of climate scenarios.”
Certainly the rapid changes seen in polar regions are paraded as the main proof of mankind’s effects on the planet and the validity of computer climate modelling. However, as we have said before, things are not that simple.
Take Antarctica. There have been major climate changes to this region over the past few thousand and few hundred years, none of them due to mankind. Ice core data reveal a pattern of often rapid changes in climate. A thousand years ago the circumpolar westerlies intensified associated with the deepening Amundsen Sea low. This is probably the most significant climate change event in Antarctica in the past five thousand years.
There have been changes in the past few hundred years as well, especially the warming of the water around the Antarctic Peninsula.
The largest annual warming trends are found on the western and northern parts of the Antarctic Peninsula, but it is a highly localised effect. Significant warming extends from the southern part of the western Antarctic Peninsula north to the South Shetland Islands. The rate of warming decreases north away from Faraday/Vernadsky (50 year long record), with the long record from Orcadas (100 year long record) in the South Orkney Islands showing a warming trend of only +0.20 deg C/ decade.
The large winter season warming of 5°C over the past 50 years at Faraday is believed to be associated with a significant decrease in winter sea ice over the Amundsen-Bellingshausen Sea. It should be stressed that the reason why there was more sea ice in the 1950s and 1960s is not known but it may have been linked to weaker or fewer storms to the west of the peninsula and greater atmospheric blocking. Indeed, a greater frequency of blocking anticyclones would have meant weaker northerly winds to the west of the Antarctic Peninsula, allowing the sea ice to advance farther north during the winter resulting in colder temperatures on the western side of the Peninsula.
The other side of the peninsula seems to be warming because of a different reason. On the eastern side the greatest warming is during the summer months and appears to be associated with the strengthening of the circumpolar westerlies since the mid-1970s. These stronger winds have resulted in more relatively warm, maritime air masses crossing the peninsula and reaching the low-lying ice shelves, as well as the adiabatic descent and warming of these winds crossing the Antarctic Peninsula’s topography.
It may be that the changes seen in the Antarctic Peninsula have little to do with the accumulation of greenhouses gasses in the atmosphere but be taking place due to the effects of ozone depletion by man-made chemicals, now since banned.
It will take the best part of a hundred years (estimates are around 2070) before the ozone hole over Antarctica is healed and levels return to what they were before it opened. In the meantime scientists have for many years seen atmospheric circulation changes in the southern hemisphere brought about by the increased UV light the ozone depletion allows through.
A number of modeling studies attribute recent summer circulation changes to ozone. The polar vortex is most pronounced in the winter stratosphere when the air above the continent is extremely cold. However, the loss of springtime ozone as a result of the ozone hole has also cooled the stratosphere through the spring and summer months. This in turn has resulted in low mean sea level pressure in the Antarctic at this time of year.
A new paper by Sarah Kang et al suggests that in the past 50 years the influence of the ozone hole has moved the westerlies poleward resulting in a changed precipitation pattern and effects on the entire southern hemisphere. They ran a series of computer models – the Canadian Middle Atmosphere odel and the United States’ National Center for Atmospheric Research (NCAR) Community Atmosphere Model.
In four experiments comparing data on sea ice, surface temperatures, precipitation and the ozone hole, the analysis showed the hole was the main driver of heavy summer rains across eastern Australia, the southwestern Indian Ocean and the Southern Pacific Convergence Zone.
Another important point is that the ozone hole is not even mentioned in the summary for policymakers issued with the last IPCC report. The fact that ozone was an unappreciated effect in terms of climate that may be a major influence is yet another reason why the last IPCC report is flawed and another example of the fact that should not have been needed to say, the science isn’t settled.
“It’s really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there — it’s just like a domino effect,” Sarah Kang, a postdoctoral research scientist in Columbia Engineering’s Department of Applied Physics and Applied Mathematics, is quoted to have said.
Lorenzo Polvani, professor of Applied Mathematics and of Earth & Environmental Sciences, senior research scientist at the Lamont-Doherty Earth Observatory, and co-author of the paper added; “We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system!”