How much have temperatures risen over the past 100 years or so? In the image below, Peter Carter points at the aerosols from volcanic eruptions and fossil fuel combustion that temporarily delay the full impact of global warming.
Temperature Rise hits Arctic most strongly
In above image, temperature anomalies are compared to a 3-decade base period from 1951 to 1980. To highlight the full wrath of global warming, it is more informative to compare anomalies with an earlier base period. Furthermore, a short running mean better shows how high peaks can reach.
NASA typically compares temperature change relative to 1951-1980, because the U.S. National Weather Service uses a three-decade period to define "normal" or average temperature. The NASA GISS analysis effort began around 1980, so the most recent 30 years at the time was 1951-1980.1
But as said, it is more informative to use a 30-year base period that starts earlier. To show Gobal & Arctic Temperature Change, James Hansen and Makiko Sato used a 1951-1980 base period next to a 1880-1920 base period. For this post, a 1883-1912 base period was selected to create the above image, and this same base period was selected to create the image below.
Above image shows that the Arctic is hit most strongly by the temperature rise. Note that the anomalies in above image are visualized by latitude, but are averaged by longitude globally, masking even higher anomalies that can be experienced at specific longitudes. At times, some areas in the Arctic do already experience anomalies of over 20°C, as shown in the animation below, based on NOAA data for the period December 7, 2011 - January 21, 2012.
|[ Note: above animation is a 3MB file that may take some time to fully load ]|
The danger is that extreme weather events will cause waters in the Arctic Ocean to warm up, in turn causing heat to penetrate deep into the seabed and triggering destablization of methane held in the sediment in the form of hydrates or free gas. Ways for this to eventuate were also recently discussed in the post Arctic Ocean is turning red.3
Feedbacks have the potential to dramatically speed up the temperature rise.
Albedo change, due to decline of snow and ice in the Arctic, exercizes a strong additional warming feedback. As illustrated by the above image by Neven, from the Arctic Sea Ice blog, average Arctic sea ice thickness (crudely calculated by dividing PIOMAS (PI) volume numbers with Cryosphere Today (CT) sea ice area numbers) is the lowest on record in the satellite era.
Another feedback is methane release. On August 25, 2013, mean global methane levels were recorded as high as 1828 ppb. On September 4, 2013, a peak methane level of 2481 ppb was recorded, showing how quickly methane levels can rise locally.
Runaway Global Warming
The danger is that, as sea ice retreats further and as methane traps more heat, there will be areas in the Arctic Ocean where cyclones will cause shallow waters to warm up all the way down to the seabed to such an extent that heat will penetrate the seabed, triggering destablization of methane held in the sediment in the form of hydrates and/or free gas. Recently, sea surface temperatures of about 20°C (68°F) were recorded in some spots in the Arctic Ocean, as also described the post Arctic Ocean is turning red.3
For more on the threat of runaway global warming, also see the methane hydrates blog.4 This situation calls for an effective and comprehensive climate plan, such as described at the ClimatePlan blog.5
1. Four Hiroshima bombs a second: how we imagine climate change
2. Warming in the Arctic
3. Arctic Ocean is turning red
4. Methane hydrates
5. Climate Plan