Week 3 - State of the climate: extreme events

I live in Cambridge, in the UK, so my nearest major climate event for 2012 was described as After experiencing dry conditions during the first three months of the year, the remainder of the year was wet, resulting in the second wettest year on record, behind 2000.

These lecture notes from the University of St. Andrews explain how warmer air can hold more water.

The UK is a collection of islands off the eastern coast of Europe. Depending on wind conditions its weather can be influenced by the Atlantic ocean or continental Europe. Hot dry winds from the east can result in drought. Warm wet winds from the west can product heavy rainfall in western areas especially where the air rises over hills and mountains.

It is difficult to like a single extreme event to climate change. However, if a trend is observed over decades then that strongly suggests that there may be a connection.

Unlike the Arctic which a frozen sea of ice formed from salt water, Antarctica is a continent covered with fresh water ice from precipitation which spreads out as ice sheets over the surrounding oceans. There are two key measures of sea ice: extent and volume.

For extent if the area covered by ice exceeds a threshold (typically 15 percent) it is counted towards the extent otherwise it is excluded. This is relatively easy to measure from satellite or aircraft photographs.

Sea ice volume also requires ice depth information. Modern satellites such as The ESA CryoSat 2 can measure sea ice (and land ice) volume.

The paper Satellite observations of Antarctic sea ice thickness and volume discusses the period 2003-2008 and observes that Sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes.

The web page Antarctica's ice loss on the rise discusses the three years from 2010 and observes the West Antarctic Ice Sheet is losing over 150 cubic kilometres of ice each year. This includes ice beyond the grounding lines which is floating on the sea.

The suggested web page Press Release: Arctic sea ice shatters previous low records; Antarctic sea ices edges to record high suggests that the Antarctic changes are due more to wind than warmth.

It is possible that the increased Antarctic ice extent could be due to wider distribution of thinner ice and could still represent a loss of sea ice volume.