Since the beginning of the Industrial Revolution, CO2 levels have increased 40% and methane levels over 250%.
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Greenhouse Gas Concentrations over last 2000 years. Source: IPCC AR4.
Greenhouse gasses have the effect of preventing heat leaving the planet. Over 90% of the extra trapped heat is absorbed by the oceans.
Global temperatures have risen 0,8C in the last century.
The Arctic ocean is losing ice at about 3000M3 per decade since 1979. Back then there was about 17,000 cubic meters of Arctic ice in September (just after northern summer). If the trend continues then it takes only 17,000/3,000 = 5.6 decades since 1979 before the arctic will be free of ice in summer. In about two decades, in 2034 the Arctic might be free of ice. Given the variance, it will probably occur somewhat sooner.[1].
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Source: Polar Science Center, Washington DC. http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/
The Arctic is warming up more rapidly because ice reflects heat (albedo) much better then water. This extra warming of the Arctic region, called Polar Amplification, is currently the largest positive feedback in the climate system.
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Source: Sam Carana, http://arctic-news.blogspot.com
A second albedo change comes from darkening of the snow cover, due to black sooth from increasing forest fires and old particles that emerge from the melting snow, collecting in the top layer.
Source: Dr. Jason Box, www.darksnow.org
Methane eruptions in the Arctic are increasing because of the heating Arctic. Russian scientists Nathalia Shakova and Igor Semiletov estimate that methane clathrates (gas molecules frozen in water) in the shallow ocean north of Siberia can be destabilized in a matter of decades, saying “It might happen today”.
Feedback loops like albedo and methane clathrates have the potential of leading to an abrupt change in global climate.
Sea levels rising indicate rising temperatures, because two sources contribute to sea level change: water temperature and melting land ice.[2]. Projections of sea level rise are uncertain, because the feedback loops seem to be highly unpredictable. Estimates for ‘business as usual’ range from about 1 meter by 2100 [3] to about 7 meters by 2070[4]. The last number is based on Paul Beckwiths observation that glacial melt rates have been doubling about every 7 years in the last few decades.
Extreme weather events are increasing rapidly. For people in coastal regions, like Miami, Bangladesh or the Netherlands, that means it will be even more difficult to keep the rising water out. The 90% of extra warming energy going into the oceans means more energy for storms and tornadoes is available. Other areas face increased drought, heat or cold.[5]
- [1] http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/ ↩
- [2] http://en.wikipedia.org/wiki/Current_sea_level_rise ↩
- [3] http://www.sciencedirect.com/science/article/pii/S0277379113004381 ↩
- [4] http://arctic-news.blogspot.nl/2014/10/where-we-are-a-climate-system-summary.html ↩
- [5] http://www.climatecommunication.org/new/features/extreme-weather/overview/ ↩