Saturday, September 14, 2013

Temperature Rise

Note: this post has been updated at:

Surface Temperature Rise

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.

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 ] 
Above animation was created by Sam Carana for the page Warming in the Arctic, which adds that the anomaly can be even more striking for individual days and locations. On January 6, 2011, the minimum temperature in Coral Harbour, located at the northwest corner of Hudson Bay in the province of Nunavut, Canada, was –3.7°C (25.3°F), i.e. 30°C (54°F) above average.

Anomalies for surface air temperatures are higher in the Arctic than anywhere else on Earth. The increase in temperature anomalies appears to be an exponential rise.

How much will temperatures rise?
Note that temperature anomalies in the above graph are again compared to the global average for the period 1951-1980.

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.

Feedbacks further accelerate warming in the Arctic

Feedbacks are described in more detail in posts such as Diagram of Doom (image below) and Changes to Polar Vortex affect mile-deep ocean circulation patterns.

Diagram of Doom
One such feedback is albedo change — retreat of Arctic sea ice results in less sunlight being reflected back into space, as further discussed in Albedo Change in the Arctic. Loss of Arctic sea ice is effectively doubling mankind's contribution to global warming. Increased absorption of the sun's rays is the equivalent of about 20 years of additional CO2 being added by man, Professor Peter Wadhams said in a BBC article.

Such feedbacks have the potential to dramatically speed up the temperature rise.

Albedo change is caused by decline of snow and ice in the Arctic, and by changes in vegetation in the Arctic. Albedo change 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. Methane emissions originate from many sources, including wetlands, burning of fossil fuel and wildfires. Methane as recorded by IASI* reached levels of up to 2571 parts per billion (ppb) on September 11, 2013.

The image below shows the peak levels that have been reached recently, as well as the highest mean methane level for each day.

One of the most threatening feedbacks is release of methane that are held in the currently frozen seabed. As the seabed warms up, it starts to release methane in what can be rather abrupt ways.

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.

The image below is part of a paper on the unfolding "Methane Catastrophe".

Back in 2008, Shakhova et al., in the study Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates? considered release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time.
Submarine pingoes: Indicators of shallow gas
hydrates in a pockmark at Nyegga, Norwegian Sea -
Hovland et al., Marine Geology 228 (2006) 15–23
As the Arctic warms up and the sea ice retreats, more cyclones can be expected to hit the Arctic Ocean. This can cause warm surface waters to be mixed down, in many places all the way down to the seabed, due to the shallow nature of many of the seas in the Arctic Ocean.

As shown on the image right and also described at the FAQ page, there can be all kinds of fractures in the sediment, while there can also be conduits where methane has escaped earlier from hydrates, allowing heat to penetrate deep into the sediment and causing methane to escape.

Methane is kept stable inside hydrates as long as the temperature remains low. Since methane expand some 160 times in volume, compared to its compressed frozen state inside the hydrate, warming of even a small part of a hydrate can cause destabilization across the entire hydrate. It may take only a small rise in temperature of a single conduit in the sediment to set off a large abrupt release of methane, which subsequently threatens to cause further releases elsewhere in the Arctic Ocean and trigger runaway global warming, as described at the methane hydrates blog.
Due to methane's high global warming potential and low levels of hydroxyl in the Arctic, this threatens to further accelerate local warming and trigger further methane releases, in a vicious spiral of runaway global warming.
from: Methane Hydrates
For more on the threat of runaway global warming, also see the methane hydrates blog. This situation calls for an effective and comprehensive climate plan, such as described at the ClimatePlan blog.

* IASI (Infrared Atmospheric Sounding Interferometer) is a hyperspectral infrared sounder residing on the European Space Agencys (ESA) MetOp series of polar orbiting satellites.

Sources and related posts