19 February 2009

from IceAgeNow Website

In May, 2008, the National Snow and Ice Data Center (NSIDC) predicted that the North Pole would be ice-free during the 2008 melt season because of ‘global warming.’

Today, they admitted that they’ve underreported Arctic ice extent by 193,000 square miles (500,000 square kilometers). They blamed the error on satellite problems and sensor drift...

Daily Arctic sea ice extent map for 15 Feb 2009

showed areas of open water that should have appeared as sea ice.
Credit: National Snow and Ice Data Center
 

And we’re supposed to trust these people? (See below reports)

193,000 square miles!

That’s the size of Maine, Vermont, Maryland, Massachusetts, New York, New Hampshire, Pennsylvania, New Jersey, Rhode Island, and West Virginia combined! And toss in Washington, D.C. for good measure.

Let’s watch the newspapers.

 

If a pimple of ice smaller than a city should break off an ice sheet, they'd holler to the high heavens. But do you think they’ll report this discovery of 'lost' ice the size of 10 states?

As opposed to the NSIDC information, AMSR-E data - compiled in cooperation with the Japan Aerospace Exploration Agency and the Advanced Earth Science and Technology Organization of Japan - shows that sea ice extent in 2009 is running ahead of 2005, 2006, 2007, and 2008.

Perhaps the NSIDC’s prediction of an ice-free north pole is premature.

Satellite Sensor Errors

...Cause Data Outage
February 18, 2009

from ArcticSeaIceNewsAndAnalysis Website

As some of our readers have already noticed, there was a significant problem with the daily sea ice data images on February 16.

The problem arose from a malfunction of the satellite sensor we use for our daily sea ice products. Upon further investigation, we discovered that starting around early January, an error known as sensor drift caused a slowly growing underestimation of Arctic sea ice extent.

The underestimation reached approximately 500,000 square kilometers (193,000 square miles) by mid-February. Sensor drift, although infrequent, does occasionally occur and it is one of the things that we account for during quality control measures prior to archiving the data. See below for more details.

We have removed the most recent data and are investigating alternative data sources that will provide correct results. It is not clear when we will have data back online, but we are working to resolve the issue as quickly as possible.

Figure 1.

Daily Arctic sea ice extent map for February 15, 2009,

showed areas of open water which should have appeared as sea ice.

Sea Ice Index data. About the data.
Credit: National Snow and Ice Data Center
 

Where does NSIDC get its data?

NSIDC gets sea ice information by applying algorithms to data from a series of Special Sensor Microwave/Imager (SSM/I) sensors on Defense Meteorological Satellite Program (DMSP) satellites.

These satellites are operated by the U.S. Department of Defense. Their primary mission is support of U.S. military operations; the data weren’t originally intended for general science use.

The daily updates in Arctic Sea Ice News & Analysis rely on rapid acquisition and processing of the SSM/I data. Because the acquisition and processing are done in near-real time, we publish the daily data essentially as is. The data are then archived and later subjected to very strict quality control. We perform quality control measures in coordination with scientists at the NASA Goddard Space Flight Center, which can take up to a year.

High-quality archives from SSM/I, combined with data from the earlier Scanning Multi-channel Microwave Radiometer (SMMR) data stream (1979–1987) provide a consistent record of sea ice conditions now spanning 30 years.

Figure 2.

Daily total Arctic sea ice extent between 1 December 2008 and 12 February 2009

for Special Sensor Microwave/Imager SSM/I

compared to the similar NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor.
Credit: National Snow and Ice Data Center

Data error sources

As discussed above, near-real-time products do not undergo the same level of quality control as the final archived products, which are used in scientific research published in peer-reviewed journals.

However, the SSM/I sensors have proven themselves to be generally quite stable. Thus, it is reasonable to use the near-real-time products for displaying evolving ice conditions, with the caveat that errors may nevertheless occur. Sometimes errors are dramatic and obvious. Other errors, such as the recent sensor drift, may be subtler and not immediately apparent. We caution users of the near-real-time products that any conclusions from such data must be preliminary.

We believe that the potential problems are outweighed by the scientific value of providing timely assessments of current Arctic sea ice conditions, as long as they are presented with appropriate caveats, which we try to do.

For several years, we used the SSM/I sensor on the DMSP F13 satellite. Last year, F13 started showing large amounts of missing data. The sensor was almost 13 years old, and no longer provided complete daily data to allow us to track total daily sea ice extent. As a result, we switched to the DMSP F15 sensor for our near-real-time analysis.

For more information on the switch, see “Note on satellite update and intercalibration,” in our June 3, 2008 post.

On February 16, 2009, as emails came in from puzzled readers, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. The problem stemmed from a failure of the sea ice algorithm caused by degradation of one of the DMSP F15 sensor channels. Upon further investigation, we found that data quality had begun to degrade over the month preceding the catastrophic failure.

As a result, our processes underestimated total sea ice extent for the affected period.

Based on comparisons with sea ice extent derived from the NASA Earth Observing System Advanced Microwave Scanning Radiometer (EOS AMSR-E) sensor, this underestimation grew from a negligible amount in early January to about 500,000 square kilometers (193,000 square miles) by mid-February (Figure 2).

While dramatic, the underestimated values were not outside of expected variability until Monday, February 16. Although we believe that data prior to early January are reliable, we will conduct a full quality check in the coming days.

Sensor drift is a perfect but unfortunate example of the problems encountered in near-real-time analysis. We stress, however, that this error in no way changes the scientific conclusions about the long-term decline of Arctic sea ice, which is based on the the consistent, quality-controlled data archive discussed above.

We are actively investigating how to address the problem. Since we are not receiving good DMSP SSM/I data at the present time, we have temporarily discontinued daily updates. We will restart the data stream as soon as possible.

Some people might ask why we don't simply switch to the EOS AMSR-E sensor. AMSR-E is a newer and more accurate passive microwave sensor. However, we do not use AMSR-E data in our analysis because it is not consistent with our historical data. Thus, while AMSR-E gives us greater accuracy and more confidence on current sea ice conditions, it actually provides less accuracy on the long-term changes over the past thirty years.

There is a balance between being as accurate as possible at any given moment and being as consistent as possible through long time periods. Our main scientific focus is on the long-term changes in Arctic sea ice.

With that in mind, we have chosen to continue using the SSM/I sensor, which provides the longest record of Arctic sea ice extent.

Ice Extent Nears Annual Maximum
March 3, 2009

from ArcticSeaIceNewsAndAnalysis Website

Arctic sea ice extent ¹ continued to increase through the month of February, as it approaches its annual maximum ². Ice extent averaged for February 2009 is the fourth-lowest February in the satellite record.

1. ice extent - the total area covered by some amount of ice, including open water between ice floes; ice extent is typically reported in square kilometers.

2. maximum ice extent - the largest sea ice extent during a given year; maximum ice extent marks the end of the growth period for sea ice, and the start of the melt season

From February 18 to 22, ice extent declined slightly, primarily because of weather conditions off the coast of Alaska; ice extent then rebounded.

Figure 1.

Arctic sea ice extent for February 2009 was 14.84 million square kilometers (5.73 million square miles).

The magenta line shows the 1979 to 2000 average extent for December.

The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
Credit: National Snow and Ice Data Center
 

Overview of conditions

Arctic sea ice extent averaged for the month of February was 14.84 million square kilometers (5.73 million square miles). February extent was 800,000 square kilometers (309,000 square miles) less than the 1979 to 2000 average, and 140,000 square kilometers (54,000 square miles) less than for February 2008.

During the month of February, Arctic sea ice extent increased by 520,000 square kilometers (201,000 square miles), an average increase of 19,000 square kilometers (7,300 square miles) per day.

These values are based on data from the F13 Special Sensor Microwave/Imager (SSM/I) sensor, which NSIDC is once again using because of problems with the sensor on the F15 satellite.

See our February 26 post for details.

Figure 2.

The graph above shows daily sea ice extent.

The solid blue line indicates 2008–2009;

the dashed green line shows 2006–2007 (the record-low summer minimum occurred in 2007);

and the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
Credit: National Snow and Ice Data Center

Conditions in context

Arctic sea ice extent continued to climb through the month of February; NSIDC scientists expect Arctic sea ice to reach its annual maximum extent sometime in March. The date of the maximum can vary by as much as 6 weeks. The average date of the maximum is March 6, based on the satellite record from 1979 to 2008.

From February 18 to 22, ice extent declined from 14.89 million square kilometers (5.75 million square miles) to 14.80 million square kilometers (5.71 million square miles), before rebounding at the end of the month.

Such ups and downs are not unusual at this time of year, as ice extent nears its annual maximum.

Figure 3.

Monthly February ice extent for 1979 to 2009

shows 2009 as the fourth-lowest February on record.
Credit: National Snow and Ice Data Center

February 2009 compared to past Februaries

Monthly average ice extent for February 2009 was the fourth lowest in the satellite record.

February 2005 had the lowest ice extent for the month; February 2006 was the second lowest; and February 2007 is in third place. Including 2009, the downward linear trend in February ice extent over the satellite record stands at –2.8% per decade.

Figure 4.

The map of sea level pressure (in millibars) over the Arctic, averaged for February 18 to 22, 2009,

shows the pressure systems that caused warm southerly winds to compact and melt the ice in the Bering Sea and Gulf of Alaska.
Credit: From National Snow and Ice Data Center

courtesy NOAA/ESRL Physical Sciences Laboratory
 

Short-term changes in winter ice extent

The temporary decline in ice extent from February 18 to 22 illustrates the sensitivity of Arctic sea ice extent to transient weather conditions.

Conditions along southern boundary of the ice cover, such as in the Bering Sea, are typically just barely cold enough for ice to exist, and the ice there can quickly expand or retreat in response to changes in temperature and winds.

The decline in mid-February appears to have been caused by the combination of low pressure centered in the western Bering Sea and high pressure centered in the western Gulf of Alaska. This weather pattern caused warm, southerly winds between the low and high pressure cells, which pushed the ice edge to the north and promoted melt.

Air temperatures in the region at the 925 millibar level (approximately 915 meters [3,000 feet] above the surface) were up to 8°C (14°F) above average.