Abrupt Local Warming

Filed in Uncategorized by on May 15, 2012 0 Comments

Back in 1958, C. David Keeling of the Scripps Institution of Oceanography started measuring levels of atmospheric carbon dioxide (CO2) at a facility of the National Oceanic and Atmospheric Administration.

The steady rise of CO2 levels over the years at Mauna Loa, Hawaii, located somewhere halfway down the globe, has become the epitome of global warming. Mean CO2 levels reached 397.17 ppm for the week that started at May 6, 2012.

Averaging things out, even over a relatively short period of one week, comes with the risk of overlooking peaks that are even more alarming. The image below, with hourly rather than weekly averages, shows one measurement actually reaching 398 ppm.

Similarly, things may look even more worrying when looking for regional peaks, rather than global averages. In the Arctic, CO2 can reach levels well over 400 ppm, as illustrated by the image below with measurements at Barrow, Alaska.

Apart from carbon dioxide, there are further greenhouse gases such as methane. The image below shows that methane levels at Mauna Loa, Hawaii, reached nearly 1.84 ppm recently. That may seem like a lot less than CO2 levels, but methane’s global warming potential is 105 times that of CO2 over a period of 20 years, and even higher over shorter periods.

Methane levels are again higher in the Arctic, as illustrated by the image below showing methane levels at Barrow, Alaska, of well over 1.9 ppm.

Figures for methane on above image are monthly averages. The situation looks even more worrying when looking at hourly averages, showing individual measurements of up to 2.5 ppm.

The danger of such high levels of greenhouse gases is that, combined with the impact of aerosols such as soot, they will cause extremely high summer temperature peaks in the Arctic.

This will speed up loss of sea ice, resulting in even further warming that threatens to cause large amounts of methane to be released from hydrates and from free gas in sediments under the water.

Is it possible for the water in the Arctic to suddenly warm up by several degrees?

Well, this has happened before. As the image on the right shows, sea surface anomalies of over 5 degrees Celsius were recorded in August 2007.

Would such warming be able to reach the bottom of the sea?

Again, this did happen in 2007, when strong polynya activity caused more summertime open water in the Laptev Sea, in turn causing more vertical mixing of the water column during storms in late 2007, according to one study, and bottom water temperatures on the mid-shelf increased by more than 3 degrees Celsius compared to the long-term mean.

Another study finds that drastic sea ice shrinkage causes increase in storm activities and deepening of the wind-wave-mixing layer down to depth ~50 m that enhance methane release from the water column to the atmosphere.

Indeed, the danger is that heat will warm up sediments under the sea, containing methane in hydrates and as free gas, causing large amounts of this methane to escape rather abruptly into the atmosphere.

Would heat be able to penetrate these sediments?

The image on the right, from a study by Hovland et al., shows that hydrates can exist at the end of conduits in the sediment, formed when methane did escape from such hydrates in the past. Heat can travel down such conduits relatively fast, warming up the hydrates and destabilizing them in the process, which can result in huge abrupt releases of methane.

Since waters can be very shallow in the Arctic, much of the methane can rise up through these waters without getting oxidized.

As the methane causes further warming in the atmosphere, this will contribute to the danger of even further methane escaping, further accelerating local warming, in a vicious cycle that can lead to catastrophic conditions well beyond the Arctic.

The image on the right shows how much carbon is present in the melting (not so permanent) permafrost.

The 2010 heatwave in Russia provides a gloomy preview of what could happen as temperatures rise at high latitudes.

Firestorms in the peat-lands, tundras and forests in Siberia could release not only huge amounts of CO2 and methane, but also soot, much of which could settle on the ice in the Himalaya Tibetan plateau, melting the glaciers there and causing short-term flooding, followed by rapid decline of the flow of ten of Asia’s largest river systems that originate there, with more than a billion people’s livelihoods depending on the continued flow of this water.

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