Changes in the Cryosphere Over Time
Trends Through 2017
Aaron Letterly and Jeff Key
11 June 2018
The cryosphere is a complex part of the climate system that experiences change on different timescales. Data collected over many years helps to distinguish long-term trends from short-term variability. The "stacked plots" below track changes for key cryospheric and cryosphere-related variables. Brief summaries of recent changes are given. The purpose is to provide a quick look at changes in the cryosphere overall. More detailed assessments of the individual cryosphere components are available through the "Other Assessments" box on the right. The information here will be updated once each year.
There have been significant changes in the Arctic climate system since 1970. At current rates, these changes may radically alter the radiative and ecological properties of the Arctic within our lifetime. Surface temperature, permafrost depth, sea ice area, snow cover, and glacial mass balance are all decisive indicators of change. Figure 1 provides time series of these variables for the Northern Hemisphere (NH) or Arctic from the beginning of their records or from 1970.
Fig. 1. Changes in the NH or Arctic from 1970-2017. From the top down: Arctic surface temperature, permafrost thaw depth in Alaska and northern Siberia, September Arctic sea ice area, March-May NH snow cover, NH glacial mass balance, and Greenland ice sheet mass anomalies. Grey lines are the 5-year running mean except for Greenland ice mass, which shows the annual averages. See below for data sources. Hover the cursor over any of the plots for a larger version. Click on the plot for a full-size version of the stacked plot in a new browser tab.
The Southern Hemisphere (SH) is dominated by oceans, and has far less land surface area than the Northern Hemisphere. The Antarctic continent, though surrounded by ice and covered in snow, is large and remote enough that data records of changes in its ice sheet are not comprehensive. Satellite-derived snow cover products have relatively large uncertainties in part because much of the SH snow cover outside of Antarctica occurs in alpine areas, which creates challenges for remote sensing. Surface temperature, sea ice area, glacial mass balance, and Antarctic Ice Sheet mass balance are decisive indicators of change to Southern Hemisphere’s climate system. Recent changes in these variables are shown below.
Fig. 2. Changes in the SH or Antarctic from 1970-2017. From the top down: surface temperature, February (summer) sea ice area, glacial mass balance, and Antarctic ice sheet mass anomalies. Grey lines are the 5-year running mean except for Antarctic ice mass, which shows the annual averages. See below for data sources. Hover the cursor over any of the plots for a larger version. Click on the plot for a full-size version of the stacked plot in a new browser tab.
Active layer thickness (ALT), or thaw depth, refers to the depth of the top layer of soil or rock that thaws during the Arctic summer before freezing again in the fall. Changes in temperature near the surface affect ALT, meaning that changes in ALT indicate a changing permafrost state for a given region. The depth of the ALT can range from a few meters in warmer, ice-rich environments to 20 m or greater in bedrock and the coldest permafrost regions. To best observe long-term change in the Arctic, continuous year-round ground temperature measurements within the upper 15 m can be analyzed. Active layer thicknesses are typically measured by mechanical probing at regular intervals, thaw-tube measurements, or inferring thaw depth based on ground temperature measurements.
Surface temperature: Extended AVHRR Polar Pathfinder (APP-x) dataset. https://www.ncdc.noaa.gov/cdr/atmospheric/extended-avhrr-polar-pathfinder-app-x
Permafrost thaw depths: Circumpolar Active Layer Monitoring (CALM), Northern Hemisphere Summary Data Table. https://www2.gwu.edu/~calm/data/north.html
September sea ice area: APP-x dataset. https://www.ncdc.noaa.gov/cdr/atmospheric/extended-avhrr-polar-pathfinder-app-x
Snowcover: Rutgers University Global Snow Lab, Monthly Area of Extent. http://climate.rutgers.edu/snowcover/table_area.php?ui_set=1&ui_sort=0
Glacial mass balance (global): World Glacier Monitoring Service (WGMS). http://wgms.ch/latest-glacier-mass-balance-data/
Greenland and Antarctica mass balance: NASA Global Climate Change, Land Ice. https://climate.nasa.gov/vital-signs/land-ice/
Thaw depth data from J.G. Mendel Station, Antarctica are courtesy of Filip Hrbáček, Masaryk University, Brno, Czech Republic.
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