A Holistic Assessment of 1979-2016 Global Cryospheric Extent

The cryosphere plays a major role in earth's climate system. Most cryospheric assessments focus on one or more of its components and their response to climate change. However, to date, there has not been a comprehensive evaluation of the entire global cryosphere. We therefore determine such a holistic estimate and quantify changes to the hemispheric and global cryosphere due to climate change, by synthesizing sea ice, snow cover, and frozen ground extents into one global cryospheric extent data set. The 1981-2010 climatology of daily global cryospheric extent ranges from 45.7 +/- 0.7 x 10(6) to 87.2 +/- 2.0 x 10(6) km(2) (9.0%-17.1%), from 13.3 +/- 0.8 x 10(6)-66.3 +/- 1.7 x 10(6) km(2) (5.2%-26.0%) in the Northern Hemisphere (NH), and from 17.9 +/- 0.3 x 10(6) to 33.6 +/- 0.4 x 10(6) km(2) (7.0%-13.2%) in the Southern Hemisphere (SH). The monthly maximum cryospheric extent of 85.84 +/- 1.91 x 10(6) km(2) occurs in December, whereas minimum occurs in July with 45.92 +/- 0.70 x 10(6) km(2). During 1979-2016, global cryospheric area extent lost approximately 87 +/- 11 x 10(3) km(2)/yr, with a decrease of 102 +/- 9.7 x 10(3) km(2)/yr in the NH that was partly offset by an increase of 14.6 +/- 4.4 x 10(3) km(2)/yr in the SH. The first day of cryospheric cover was delayed by 3.6 days at a rate of 0.95 days/decade, and the last day advanced by 5.7 days, at a rate of 1.5 days/decade. The duration and number of cryospheric cover days decreased by 8.7 days and 7.6 days over the study period, respectively. These variations of global cryospheric extent are correlated with rising air temperatures. Our findings highlight the importance of assessing the cryosphere as a whole, and provide a way to quantitatively estimate its overall changes.