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March 25th

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GEOG 205
Gail Chmura

th March 25 , 2013  we will be finishing the lecture from last time  lecture slides still under March 20  review: o change in coastal wind strength  studies have shown increase in coastal winds (1946-1989) o Ekman transport  there is a combination of wind and the Coriolis effect that transports water o satellite measurements  measure bottom 8 km (source of error); orbital drift; calibrating these instruments; satellite record shorter than written record so uncertainty principle o confirming warming temperatures  should since evidence in glaciers, sea ice & ice sheets as they melt due to warming temperatures o Martin Grosjean  “the current meltdown is simply not normal” o glacier retreat can’t conclusively be tied to higher temperatures as it’s impacted by precipitation changes o global evidence indicates that the majority of glaciers around the world are in retreat, which fits with warming world  changes in ice/snow cover o sea ice  there are differences between the Arctic & Antarctica  Antarctica is a continent, but the Arctic is in the north pole region that includes many islands & borders a number of countries like Canada, Russia & Greenland  sea ice in Arctic much less mobile due to the countries surrounding it  floes (broken off pieces of glacier) more prone to converge or bump into each other & pile up into thick ridges  presence of ridge ice & its longer life cycle leads to ice that stays frozen longer during the summer melt  some Arctic sea ice remains through summer 7 continues to grow through autumn  almost all sea ice that forms during Antarctic winter melts during summer  there has been a dramatic decrease in he amount of Arctic sea ice  sea ice found in polar regions where surface ocean layer freezes  max. in late winter & min in late summer  don’t see reductions in winter since few degrees change doesn’t have much effect 2  in 1970s it averaged ~ 8 million km a year  less than 3.5 million in 2012  could be ice-free in summer months within 20 years  artic amplification  observation shows Arctic is warming faster than forecasted  potential causes o changes in cloud cover, water vapour  less sea ice means surface of ocean is able to evaporate more o changes to oceanic/atmospheric circulation  ocean currents might bring more warmer waters into the Arctic preventing the formation of sea ice o decrease in sea ice/snow cover  decreases the amount of albedo & therefore increases temperatures (since radiation lost to reflection is now absorbed)  Screen & Simmonds in Nature 2010 posit that it’s decrease in albedo from loss of sea ice speeds up warming  supports radiation lost to reflection now absorbed  role of other cause still remains uncertain  this creates a positive feedback: ocean absorbs more heat  temperature rises  sea ice melts  albedo decreased  ocean absorbs more heat, etc.  there is actually an increase in sea ice in the Antarctic  is this proof against global warming?  southern ocean surface temperatures are increasing faster  there is a drop in ozone levels above Antarctica & strengthens the winds that move sea ice around which also increases open areas of water that increases the production of sea ice  sea ice summary  dramatic decreases in Arctic but surprising increases in Antarctic (due to ozone hole & circumpolar current)  consistent with warming world o ice sheets  Greenland ice sheet  80% of surface of Greenland  second largest ice body in world  covers 1 710 000 km 2  thickness generally more than 2 km & over 3 km at thickest point  mass decreases
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