Friday, May 29, 2015

Arctic ice: A modest rally

Arctic-ice coverage reached a four-year October high last month, but decadal trend still negative, government says.

Arctic ice: A modest rally

For the first October since 2009, Arctic ice, a key global-warming indicator, covered more than 3 million square miles last month, according to the National Snow and Ice Data Center.

While the growth outpaced the 1981-2000 average by about 15 percent, it didn’t grow quite as rapidly as it did last October, and the overall ice has decreased at a rate of about 7 percent per decade, the center said.

This is an addendum to the global-temperature report we posted yesterday from the National Climate Data Center in which NCDC did not include an ice update.

Melting ice is a significant contributor to warming in the Arctic region, which has outdone that of the rest of the world as Arctic sea-surface waters have been exposed to the sun.

To recap, NCDC found that worldwide land-and-sea surface temperatures averaged 1.13 degrees Fahrenheit above the 20th Century average of 60.6 for October.

That would make it the seventh-warmest October in the period of record, dating to 1880.

We had to go back to February 1985 in the NCDC dataset to find a monthly temperature below the 20th Century average.

While the above-normal streak is impressive, we note that all disaster scenarios aside, in real life worldwide warming is not a spectator sport and not for those lacking stomachs for tedium.

Overall temperature changes generally have been incremental, and it would be surprising if a month or year came in beneath the 20th Century averages anytime soon, given how ponderously the whole planet changes temperature.

The average inter-annual changes in the period of NCDC record, dating to 1880, have been on the order of 0.14 degrees Fahrenheit, in either direction, with the increases outnumbering decreases by eight years.

The largest swings we found were a 0.46 degree Fahrenheit increase, 1977 vs. 1976 to 1977, and a nearly parallel 0.47 degree decrease, 1964 vs. 1963.

Last year was the 10th warmest on record, and even if one subtracted that record-level 0.47 degrees from the 2012 number, it would have come it at about 0.58 degrees above the 20th Century average and finish in the top 25 warmest.

As for month-to-month changes, the biggest in the dataset would be just under 1 degree Fahrenheit. Shave off that record-level decrease from the October 2013 temperature, and it stil would be comfortably above average.

While the warming so far may have occurred at a glacial pace, computer models and various experts continue to insist that acclerartion is all but inevitable.

We'll keep watching.

Inquirer Weather Columnist
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Tony Wood Inquirer Weather Columnist
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