Forces behind Superstorm Sandy

Superstorm Sandy hit North America's east coast in a devastating way. This justifies an analysis of the forces behind Sandy and the links with global warming and climate change.

Global warming causes temperatures of oceans and the atmosphere to rise. A warming Gulf Stream fuels hurricanes traveling north along North America's east coast.

More heat translates into more wind; specifically, stronger hurricanes are getting stronger over the years, as illustrated by the inmage on the right from James Elsner et al. (2008).

Additionally, sea levels are rising, especially on the Atlantic coast of North America, which is a hotspot of accelerated sea-level rise, as described in a study by Sallenger et al. (2012).

Generally, global warming will cause more extreme weather events, says James Hansen (2012). This is especially the case for heavy rainfall events, since global warming causes more evaporation of seawater, while warm air can also carry more water. According to Kevin Trenberth (2011), the water holding capacity of air increases by about 7% per 1°C warming, which leads to increased water vapor in the atmosphere. Hence, storms, whether individual thunderstorms, extratropical rain or snow storms, or tropical cyclones, supplied with increased moisture, produce more intense precipitation events. All this leads to a greater hurricane danger; they can be expected to be stronger and wetter, causing flooding and further devastation along the east coast of North America.

The situation in the Arctic is making things even worse. Several studies, such as by Jennifer Francis (2012), by Greene et al. (2012) and by Liu et al. (2012), show that atmospheric circulation is changing as a result of sea ice loss. This circulation change results in more frequent episodes of blocking patterns that lead to increased cold surges over large parts of northern continents. Moreover, sea ice loss results in an increase in atmospheric water vapor content in the Arctic region during late autumn, and this provides enhanced moisture sources.

More open water in the Arctic Ocean results in more warming of the overlying atmosphere. This warming can be expected to change precipitation. An analysis by Julienne Stroeve (2011) shows an autumn increase in cyclone-associated precipitation over the past decade, linked to a shift in atmospheric circulation towards more frequent and more intense cyclones in the Atlantic sector of the Arctic.

The authors added that more research was needed; indeed, the devastation caused by Sandy calls for further analysis. Warming in the Arctic is accelerating at a pace several times that of the rest of the world, as a result of multiple feedbacks as described in the post Diagram of Doom; changing of the jet stream is only one out of multiple feedbacks.

Changes to the jet stream were behind Sandy's path inland. A strong and prolonged high pressure area over Greenland blocked Sandy from going north or east. This also caused it to spread out and to hang around for such a long time.

Big changes are taking place in the Arctic, in terms of sea ice loss, snow line retreat and albedo change in Greenland. Without more effective action on climate change, weather events like this can therefore be expected to hit the east coast of North America more often and with increasing force in future.


References

- The increasing intensity of the strongest tropical cyclones, James Elsner et al. (2008)
http://www.nature.com/nature/journal/v455/n7209/abs/nature07234.html

- Hotspot of accelerated sea-level rise on the Atlantic coast of North America, Asbury Sallenger et al. (2012)
http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1597.html

- Perception of climate change, James Hansen et al. (2012)
http://www.pnas.org/content/109/37/E2415

- Changes in precipitation with climate change, Kevin Trenberth (2011)
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/SSD_Trenberth_2nd_proof.pdf

- Linking Weird Weather to Rapid Warming of the Arctic, Jennifer Francis (March 2012)
http://e360.yale.edu/feature/linking_weird_weather_to_rapid_warming_of_the_arctic/2501/

- An Arctic wild card in the weather, Chuck Greene and Bruce Monger (2012)
http://www.tos.org/oceanography/archive/25-2_greene.html
http://www.news.cornell.edu/stories/June12/arcticWildcard.html

- Impact of declining Arctic sea ice on winter snowfall, Jiping Liu et al. (2012)
http://www.lasg.ac.cn/UpLoadFiles/File/papers/2012/2012-pnas.jiping_liu.pdf

- Attribution of recent changes in autumn cyclone associated precipitation in the Arctic, Julienne Stroeve et al. (2011)
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0870.2011.00515.x/abstract
http://www.tellusa.net/index.php/tellusa/article/view/15846/17736
poster at:
http://soa.arcus.org/sites/soa.arcus.org/files/sessions/2-3-arctic-change-and-natural-variability/pdf/stroeve.pdf

Related

- Warming Gulf Stream causes methane release
http://arctic-news.blogspot.com/2012/10/warming-gulfstream-causes-methane-release.html

- Diagram of Doom
http://arctic-news.blogspot.com/2012/08/diagram-of-doom.html

- Opening further Doorways to Doom
http://arctic-news.blogspot.com/2012/08/opening-further-doorways-to-doom.html

- Climate Change Sandy Says to US: 'Take That, Idiots!'
http://arctic-news.blogspot.com/2012/10/climate-change-sandy-says-to-us-take-that-idiots.html

- Hurricane Sandy moving inland
http://arctic-news.blogspot.com/2012/10/hurricane-sandy-moving-inland.html

- Big changes in Arctic within years
http://arctic-news.blogspot.com/2012/10/big-changes-in-arctic-within-years.html

NSIDC calls record 2012 low

This NASA satellite image shows how the Arctic sea ice extent, on Sept. 16, 2012, compares to the average
minimum extent over the past 30 years (in yellow). Credit: NASA/Goddard Scientific Visualization Studio.

Arctic sea ice cover likely melted to its minimum extent for the year on September 16, says the National Snow and Ice Data Center (NSIDC), adding the note that this number is preliminary—changing weather conditions could still push the ice extent lower.

Sea ice extent—defined by NSIDC as the total area covered by at least 15 percent of ice—fell to 3.41 million square kilometers (1.32 million square miles), now the lowest summer minimum extent in the 33-year satellite record.

NSIDC adds that this minimum is 49% below the 1979 to 2000 average, as illustrated by the table below.

Table 1. Previous minimum Arctic sea ice extents

YEAR	MINIMUM ICE EXTENT		DATE
	IN MILLIONS OF SQUARE KILOMETERS	IN MILLIONS OF SQUARE MILES
2007	4.17	1.61	September 18
2008	4.59	1.77	September 20
2009	5.13	1.98	September 13
2010	4.63	1.79	September 21
2011	4.33	1.67	September 11
2012	3.41	1.32	September 16
1979 to 2000 average	6.70	2.59	September 13
1979 to 2010 average	6.14	2.37	September 15

NSIDC adds that the six lowest seasonal minimum ice extents in the satellite record have all occurred in the last six years (2007 to 2012). In contrast to 2007, when climatic conditions (winds, clouds, air temperatures) favored summer ice loss, this year’s conditions were not as extreme. Summer temperatures across the Arctic were warmer than average, but cooler than in 2007. The most notable event was a very strong storm centered over the central Arctic Ocean in early August. It is likely that the primary reason for the large loss of ice this summer is that the ice cover has continued to thin and become more dominated by seasonal ice. This thinner ice was more prone to be broken up and melted by weather events, such as the strong low pressure system just mentioned. The storm sped up the loss of the thin ice that appears to have been already on the verge of melting completely.

NASA says that this year, a powerful cyclone formed off the coast of Alaska and moved on August 5 to the center of the Arctic Ocean, where it churned the weakened ice cover for several days. The storm cut off a large section of sea ice north of the Chukchi Sea and pushed it south to warmer waters that made it melt entirely. It also broke vast extensions of ice into smaller pieces more likely to melt.

“The storm definitely seems to have played a role in this year's unusually large retreat of the ice”, said Claire Parkinson, a climate scientist at NASA Goddard Space Flight Center, Greenbelt, Md. “But that exact same storm, had it occurred decades ago when the ice was thicker and more extensive, likely wouldn't have had as prominent an impact, because the ice wasn't as vulnerable then as it is now.”

In the press release, NSIDC lead scientist Ted Scambos said that thinning ice, along with early loss of snow, are rapidly warming the Arctic. “But a wider impact may come from the increased heat and moisture the warmer Arctic is adding to the climate system,” he said. “This will gradually affect climate in the areas where we live,” he added. “We have a less polar pole—and so there will be more variations and extremes.”

The image below, from Arctic Sea Ice Blog, shows Arctic sea ice observations (in red) against the backdrop of models used in IPCC AR4 (2007) for projection of sea ice up to the year 2100.

The image below, from NSIDC sea ice news, shows the observed September sea ice extent for 1952-2011 (black line) against a backdrop of projections used by IPCC AR4 (blue) as well as proposed for use in IPCC AR5 (red).

Note: The record low value for 2012 still has to be added on this image. Credit: NSIDC, Stroeve et al.

The image shows that the recently observed decline in sea ice extent is steeper than the CMIP3 models with a “business as usual” SRESA1B greenhouse gas emissions scenario (blue line), as used by the IPCC in AR4.

It is also steeper than the more recent CMIP5 models using a RCP 4.5 scenario (pink line) that are proposed to be used by the IPCC in AR5.

RCP 4.5 is a scenario in which the global temperature rise would would soon exceed 2 degrees Celsius. Since the Arctic experiences accelerated warming, such a scenario would clearly be catastrophic. Looking at sea ice volume, rather than extent, would show this even more clearly.

Below, a NOAA animation showing sea ice decline in 2012 and a NASA animation showing the Arctic cyclone.