CLIMATE CHANGE

FEBRUARY 2018 was the sixth warmest February since 1880. It was +1.060C above the 1880-1920 period that gives us our best estimate of preindustrial global temperature. Last month was very cold in Japan, Western Europe and North America yet the Arctic was 8-120C warmer than normal.

There is now evidence (Cohen et al. 2018), that the frequency of cold Arctic air meandering south is now increasing due to global warming. This is a paradoxical concept for some people to understand that global warming can result in regional cooling. The Arctic is warming more than the global average due to the loss of sea ice. This is called a positive climate feedback response. We expect summer sea ice to be non-existent by 2030, so if you are a polar bear, that’s bad.

So how does a warming Arctic create cooler winters in the northern hemisphere? The warmer Arctic reduces the temperature gradient (difference) between the Arctic and the equator. This weakens the mid-latitude jet stream that allows more cold Arctic air to meander further south resulting in longer cooler cold periods.

The Southern Ocean is different because it is warming more slowly than the Arctic because of the cooling effects of more fresh water being released from Antarctica (Hansen et al. 2016). This is because fresh water floats above salt water and freezes at a higher temperature.

Unfortunately, because the Southern Ocean is so cold, it is absorbing more CO2 than warmer oceans which means it is acidifying faster than other oceans.

If we continue to burn fossil fuels at the current rate we are on track to warm the globe by an average of two degrees by about 2035 or possibly much sooner. The last time earth was two degrees warmer than pre-industrial temperature was 125 000 years ago in the Eemian period when sea levels were six to nine metres higher than today.

GEOFF CASTLE, M.Sc researcher, Toowoomba