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New measurements taken during the summer solstice in the Arctic reveal a decrease of 20-35% in reflected sunlight from north of 80°N. This decrease in reflected sunlight corresponds with a 7-9% decrease in Arctic sea ice coverage during the same period. These findings suggest that not only is the Arctic sea ice receding, but its albedo is also decreasing.

Comparisons with measurements taken in the Antarctic provide a baseline for understanding these changes. Reflected sunlight in the Antarctic, south of 80°S, is up to 30% larger than in the Arctic and remains consistent around the solstice. Additionally, measurements taken 20 days after the solstice show that Arctic reflected sunlight is over 100W/m2 less than Antarctic reflected sunlight. This amount of heat is enough to melt more than 1 mm of ice per hour.

These measurements were obtained using pixelated radiometers on Global Positioning System satellites from 2014 to 2019. The satellites’ orbits provide continuous views of 37% of the Earth, allowing for two daily full views of the Arctic and Antarctic. Additionally, the GPS constellation offers full-time, full-Earth coverage, supplementing other instruments with a more synoptic view of the Earth.

The rapidly changing climate in the Arctic has led to phenomena such as a nearly 40% decrease in minimum sea ice extent since the 1970s. Various theories, including reduced summer albedo, increased water vapor content, and changes in cloudiness and heat transport, have been proposed to explain the heightened warming in the Arctic compared to other regions.

Climate models have suggested that sea ice albedo feedbacks play a significant role in driving Arctic Amplification. These feedbacks occur when melting sea ice leads to a recession in the ice pack and a decrease in remaining ice’s reflectivity. However, comprehensive long-term measurements of Arctic albedo are limited.

The pixelated radiometers on the GPS satellites provide valuable data for understanding Earth’s radiation balance. While the radiometers have narrower spectral coverage than other instruments, they offer full-time coverage of reflected sunlight in the polar regions, which are not visible from geosynchronous orbits. The multiple simultaneous views of the Earth also allow for sampling of angular reflectance variations.

In conclusion, the new measurements of Earth-reflected sunlight confirm the rapid decrease in Arctic sea ice albedo and shed light on the role of sea ice albedo in Arctic Amplification. Further analysis of these measurements and comparison with climate models and reanalysis data will help quantify the impact of sea ice albedo on the changing Arctic climate.

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