Arctic sea ice bottoms out near all-time low; August was Earth's 4th - 8th warmest

Arctic sea ice extent hit its minimum on September 9 this year, falling to its second lowest value since satellite measurements began in 1979, according to the National Snow and Ice Data Center . More than one third (35%) of the Arctic sea ice was missing this summer, compared to the 1979 - 2000 average. This is an area about the size of the Mediterranean Sea. The 2011 sea ice minimum was very close to the all-time record low set in 2007; in fact, the University of Bremen rated the 2011 loss the greatest on record. For the fourth consecutive year, and fourth time in recorded history, ice-free navigation was possible in the Arctic along the coast of Canada (the Northwest Passage), and along the coast of Russia (the Northeast Passage.) Mariners have been attempting to sail these waters since 1497.

While the record low sea ice year of 2007 was marked by a very unusual 1-in-20 year combination of weather conditions that favored ice loss (including clearer skies, favorable wind patterns, and warm temperatures), 2011's weather patterns were much closer to average. The fact we pretty much tied the record for most sea ice loss this year despite this rather ordinary weather is a result of the fact that large amounts of thicker, multi-year ice has melted or been flushed out of the Arctic since 2007. As a result of the loss of this old, thick ice, both 2010 and now 2011 set new records for the lowest volume of sea ice in the Arctic, according the University of Washington PIOMAS model. Given the very thin ice now covering most of the Arctic, we can expect truly dramatic sea ice loss the next time 1-in-10 year or 1-in-20 year warmth and sunshine invades the Arctic. We are definitely on pace to see the Arctic virtually sea ice-free in summer by 2030, as predicted by several leading Arctic sea ice scientists. I expect we'll see more than half of the Arctic ice gone and the North Pole liquid instead of solid by the summer of 2020, and probably sooner.


Figure 1. Arctic sea ice extent in 2011 (blue line) compared to the record low year of 2007 (dashed green line) and average (thick grey line.) Image credit: National Snow and Ice Data Center .

When was the last time the Arctic was this ice-free?
We can be sure the Northwest Passage was never open for ice-free navigation--particularly ice-free navigation for multiple years in a row--between 1900 and 2000, as we have detailed ice edge records from ships (Walsh and Chapman, 2001). It is very unlikely the Passage was open between 1497 and 1900, since this spanned a cold period in the northern latitudes known as "The Little Ice Age". Ships periodically attempted the Passage and were foiled during this period, and the native Inuit people have no historical tales of the Passage being navigable at any time in the past.

The Northwest passage may have been open multiple years in a row for ice-free navigation at some period during the Medieval Warm Period, between 1000 and 1300 AD. A better candidate was the period 6,000 - 8,500 years ago, when the Earth's orbital variations brought more sunlight to the Arctic in summer than at present. Funder and Kjaer (2007) found extensive systems of wave generated beach ridges along the North Greenland coast that suggested the Arctic Ocean was ice-free in the summer for over 1,000 years during that period. Prior to that, the next likely time was during the last inter-glacial period, 120,000 years ago. Arctic temperatures then were 2 - 3°C higher than present-day temperatures, and sea levels were 4-6 meters higher.

However, it is possible that the recent summer low-ice conditions in the Arctic are unprecedented for the past 800,000 years, according to a 2011 press release by Project CLAMER, a European group dedicated to climate change and European marine ecosystem research. They found that a tiny species of plankton called Neodenticula seminae that went extinct in the North Atlantic 800,000 years ago has become a resident of the Atlantic again, having drifted from the Pacific through the Arctic Ocean thanks to dramatically reduced polar ice. The 1999 discovery represents "the first evidence of a trans-Arctic migration in modern times" related to plankton, according to the UK-based Sir Alister Hardy Foundation for Ocean Science, whose researchers warn that "such a geographical shift could transform the biodiversity and functioning of the Arctic and North Atlantic marine ecosystems."

It is possible we'll have a better idea of historical ice-free conditions in the Arctic in the next few years. A new technique that examines organic compounds left behind in Arctic sediments by diatoms that live in sea ice give hope that a detailed record of sea ice extent extending back to the end of the Ice Age 12,000 years ago may be possible (Belt et al., 2007). The researchers are studying sediments along the Northwest Passage in hopes of being able to determine when the Passage was open during the past 12,000 years.

References
Belt, S.T., G. Masse, S.J. Rowland, M. Poulin, C. Michel, and B. LeBlanc, "A novel chemical fossil of palaeo sea ice: IP25", Organic Geochemistry, Volume 38, Issue 1, January 2007, Pages 16-27.

Funder, S. and K.H. Kjaer, 2007, "A sea-ice free Arctic Ocean?", Geophys. Res. Abstr. 9 (2007), p. 07815.

Walsh, J.E and W.L.Chapman, 2001, "Twentieth-century sea ice variations from observational data", Annals of Glaciology, 33, Number 1, January 2001 , pp. 444-448.

August 2011: Earth's 4th - 8th warmest on record
August 2011 was the globe's 8th warmest August on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated August the 4th warmest on record. Land temperatures during August were the 2nd warmest on record, and ocean temperatures were the 12th warmest on record. Ocean temperatures in the Atlantic Ocean's Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America between 10°N and 20°N latitude, were 0.8°C above average, the 4rd warmest August on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 6th or 3rd warmest in the 34-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH). For more details on global extremes during August, see the details from weather historian Christopher C. Burt.


Figure 2. Departure of temperature from average for August 2011. Image credit: National Climatic Data Center (NCDC).

Maria hits Newfoundland
Hurricane Maria hit Newfoundland, Canada yesterday afternoon near 3:30 pm local time as a Category 1 hurricane with 75 mph winds. However, the hurricane's strongest winds were over water, and the storm brought very little in the way of strong winds or heavy rain to the island. Cape Race at the southeast tip of Newfoundland saw sustained winds of 41 mph, gusting to 54 mph at 3:30 pm Friday as the center of the storm passed. Winds in the capital of St. John's peaked at 37 mph, gusting to 46 mph, at 10:30 am local time. Maria's strike makes this Newfoundland's second consecutive year with a hurricane strike, something that has never occurred since hurricane record keeping began in 1851. Last year, Hurricane Igor killed one person on Newfoundland, and damage exceeded $100 million, making Igor the most damaging tropical cyclone in Newfoundland history.


Figure 3. Satellite image of Hurricane Maria taken at 12:15 pm EDT September 16, 2011. At the time, Maria was a Category 1 hurricane with 75 mph winds. Image credit: NOAA Environmental Visualization Lab.

Invest 97L
For the first day since August 18, we don't have a named storm in the Atlantic. However, we have a new area to watch. A tropical wave that moved off the coast of Africa Friday and is now 300 miles south of the Cape Verde Islands is moving west at 10 - 15 mph. The wave has developed a modest amount of heavy thunderstorm activity and spin, and has been designated Invest 97L by NHC. Wind shear as diagnosed by the SHIPS model is light, 5 - 10 knots, and is predicted to stay light to moderate through Tuesday morning. Ocean temperatures are 27.5°C, one degree above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 97L is embedded in a moist environment.

Most of the models develop 97L into a tropical depression by Tuesday; NHC gave the disturbance a 20% chance of developing into a tropical depression by Monday in their 2 pm Tropical Weather Outlook. 97L should head west or west-northwest towards the Lesser Antilles over the next six days, and could arrive in the islands as early as Friday--though most of the models predict a later arrival. It is likely 97L will encounter the usual troubles storms this year have had with wind shear and dry air on the long trek across the Atlantic.

I'll have a new post on Monday, when I'll discuss the long-range hurricane outlook for the rest of September.

Jeff Masters