Inconveniently timed data processing problems at the National Snow and Ice Data Center (NSIDC) have slowed analysis, but at the pan-Arctic scale new sea ice is now forming as the solar heating is rapidly decreasing. Daily extent data from NSIDC is currently not available Sept 12 to 17. It’s possible some of the values/dates in this post will change slightly if/when the missing data is processed and when the usual annual reprocessing is completed.
Arctic Sea Ice Extent Minimum
For the Arctic as a whole, the minimum sea extent of 4.28 million km² occurred on September 11 based on National Snow and Ice Data Center data. If this date holds, it is the earliest minimum extent since 2016, when the low point was reached on September 10. The other widely used source of Arctic Sea ice extent information is provided by the Japan Aerospace Exploration Agency (JAXA), which uses a different satellite and processing, and data was not interrupted. This data set shows the annual minimum extent occurred on September 13.
As shown in Fig. 1, this year’s minimum was very close to the 2023 minimum and the seventh lowest overall, all of which have occurred since 2012.
The trend in sea ice minimum during the past 46 years is not linear, with a slower rate of decline since about 2010. The reasons for this are complex and involve long term variations in ocean and atmospheric circulations, but one factor is likely to be that southern ice is nowadays melting away and the remaining ice at the end of the melt season is mostly confined to north of 78°N, where the duration of significant solar heating (as opposed to daylight) is much shorter than farther south.
2024 Arctic sea ice minimum in historic context
Figure 2 puts this year’s minimum extent in spatial context. On the left is the median sea ice extent on the day of the annual during the first 11 years of the satellite era: this avoids cherry-picking a year for comparison. The differences are obvious and are especially large in the Asian and Alaska sectors (Kara Sea eastward to the Beaufort Sea).
Sea ice near Alaska
The daily sea ice extent in the Beaufort Sea has been either second or third lowest since early August. The 2024 minimum appears to have occurred on September 11 as the second lowest on record, only a bit higher than the record low extent in 2012. Per Fig. 3, this is the second consecutive summer with exceptionally low end of melt season ice extent in the Beaufort Sea: 2023 was the second lowest minimum extent but is now bumped to third place. Combined with low sea ice in the Canadian Archipelago, there were many successful transits of the Northwest Passage in late summer by non-ice hardened vessels.
The Chukchi Sea presents a very interesting story. As of mid-September (Fig. 4), the National Weather Service Alaska region sea ice concentration analysis shows open water extends to north of 75°N over the eastern Chukchi Sea, while low to moderate concentration ice remained north and northeast of Wrangel Island. However, the most eye-catching feature is the moderate to high concentration ice that has persisted all summer from Wrangel Island southeast to the northeast Chukotka coast. A convergence of factors resulted in ice surviving through the summer in this area. During the spring, persistent and sometimes strong north winds repeatedly pushed ice into this area, causing the ice to raft, effectively thickening the ice. This summer, there have been reports that much of the visible ice is streaked with dirt and gravel, an indication that some ice was pushed right down to the ocean floor by the weight of overlying ice. Then, in early summer, it was cloudy and cool, which limited melting during the time of maximum solar heating. In the 20th century it was not at all unusual to have ice persist all summer in this region, but we have to go back to 1998 to find significant amounts of sea ice so far southeast in mid-September (in 2000 and 2001 there was September ice to the Chukotka coast from Wrangel Island westward).
Overall, the Chukchi Sea minimum extent (Fig. 5) was propped up by this remnant “southern ice”, and so was much higher than the negligible ice area remaining at the end of the melt season in some recent years, but it significantly less than 2021, and of course far lower than was usual in the later 20th century.