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Sunday, April 23, 2017

IPCC Shows Growth in Arctic Ice Caps






















Note that, since Antarctic ice is about 10X in mass Arctic ice, this means that from 1979-2012 there was a 1.1-1.15%/decade growth in the combined ice caps over this time period.

Continuing the trends reported in AR4, there is very high confidence that the Arctic sea ice extent (annual, multi-year and perennial) decreased over the period 1979–2012 (Figure TS.1). The rate of the annual decrease was very likely between 3.5 and 4.1% per decade (range of 0.45 to 0.51 million km2 per decade). The average decrease in decadal extent of annual Arctic sea ice has been most rapid in summer and autumn (high confidence), but the extent has decreased in every season, and in every successive decade since 1979 (high confidence).

The extent of Arctic perennial and multi-year ice decreased between 1979 and 2012 (very high confidence). The rates are very likely 11.5 [9.4 to 13.6]% per decade (0.73 to 1.07 million km2 per decade) for the sea ice extent at summer minimum (perennial ice) and very likely 13.5 [11 to 16] % per decade for multi-year ice. There is medium confidence from reconstructions that the current (1980–2012) Arctic summer sea ice retreat was unprecedented and SSTs were anomalously high in the perspective of at least the last 1,450 years. {4.2.2, 5.5.2}

It is likely that the annual period of surface melt on Arctic perennial sea ice lengthened by 5.7 [4.8 to 6.6] days per decade over the period 1979–2012. Over this period, in the region between the East Siberian Sea and the western Beaufort Sea, the duration of ice-free conditions increased by nearly 3 months. {4.2.2}

There is high confidence that the average winter sea ice thickness within the Arctic Basin decreased between 1980 and 2008. The average decrease was likely between 1.3 m and 2.3 m.

High confidence in this assessment is based on observations from multiple sources: submarine, electromagnetic probes and satellite altimetry; and is consistent with the decline in multi-year and perennial ice extent. Satellite measurements made in the period 2010–2012 show a decrease in sea ice volume compared to those made over the period 2003–2008 (medium confidence). There is high confidence that in the Arctic, where the sea ice thickness has decreased, the sea ice drift speed has increased. {4.2.2}

It is very likely that the annual Antarctic sea ice extent increased at a rate of between 1.2 and 1.8% per decade (0.13 to 0.20 million km2 per decade) between 1979 and 2012 (very high confidence). There was a greater increase in sea ice area, due to a decrease in the percentage of open water within the ice pack. There is high confidence that there are strong regional differences in this annual rate, with some regions increasing in extent/area and some decreasing. There are also contrasting regions around the Antarctic where the ice-free season has lengthened, and others where it has decreased over the satellite period (high confidence). {4.2.3}

Natural science

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