GeoData Center Project: ALISONLake Ice and Snow Science

WHY STUDY LAKE ICE AND SNOW?

Introduction

A MODIS image of snow cover extent over North America on 16 October 2001.

Snow cover and frozen lakes and ponds are a critical water resource in many areas. More than 75 percent of the water for human consumption and irrigation in the western United States comes from snow melt runoff.

The presence of snow significantly modifies land/atmosphere interaction because of its high albedo and low thermal conductivity (i.e., its ability to transfer heat from layer to layer). Similarly, the presence of ice cover on a pond, lake or river impacts water/atmosphere interactions.

For three quarters of the year, Alaska is covered by snow and ice (over 1.7 million km² or almost 657 million mile² of land). This MODIS image was taken on 29 March 2002.

A MODIS image acquired on 7 June 2002, shows that the snow has melted from the tundra on the North Slope of Alaska (brown) but that most of the lakes are still frozen (white). Beaufort Sea and Chukchi Sea sea ice is present along the coast.

Changes in Arctic Air Temperatures

Evidence from ice cores, lake cores and tree rings indicate that the earth’s temperature has been slowly warming over the last 400 years. Satellite data also show a surface temperature warming trend. In the past 30 years, winter temperatures have increased by 6°C in parts of Alaska and northern Eurasia.

Source: NASA.
The figure above shows how much air temperatures near the Earth’s surface changed relative to the global mean temperature from 1951 to 1980. Red and orange colors indicate higher temperatures especially in Northern Canada, Alaska and Siberia(deeper reds). The blue shades for negative numbers represent cooling.

This image shows the winter temperature trend in the Arctic from 1966 to 1995. The scale is in degrees Celsius per decade.
Source: NASA.

These data show the deviation of the mean annual Arctic temperature from the long term normal annual temperature from 1990-2002.

Changes in Freshwater Ice

There is ample evidence that freshwater ice freeze-up, break-up and ice duration (referred to as phenology) are primarily a function of weather and climate, particularly air temperature.

Northern Hemisphere data (right; Magnuson et al., 2000) show a trend towards:

• later freeze-up,
• earlier break-up and
• shorter ice duration (decrease of 20 days since 1845).

This equals a temperature change of 1.2°C per 100 years.

The Nenana Ice Classic data document the first movement of ice on the Tanana River. As of spring 2004, break-up was occurring 5.2 days earlier relative to the vernal equinox in 1917. The advance of break-up is strongly related to rising spring mean air temperatures.
More information: Nenana Ice Classic data.

Note: Break-up dates trend downwards (earlier), freeze-up dates trend upwards (later) and duration values trend downwards (shorter).
Source: Magnuson et al. (2000) and NSIDC.

Changes in Snow

Snow cover exhibits considerable interannual variation in response to the natural variability of atmospheric circulation patterns which affect both snowfall and temperature. Factors that affect snowmelt include: amount of snowfall, air temperatures and cloud cover.

During the winter of 1999/2000 there was less snow than usual over North America. This image is a MODIS eight-day composite map showing maximum snow cover from March 5-12, 2000.

• Snow is white
• non-snow covered land is green
• clouds are grey
• water is blue

The red line represents the "average" March snow line, and the yellow line represents the "average" February snow line, as determined from NOAA/NESDIS snow maps (1966-present).
Source: NASA

The top graph shows a comparison of six time-series of melt dates in northern Alaska with the 1966-2000 Barrow (BRW) melt date record. A 5-year smoothed time-series and linear fits are shown. Each is correlated with the NOAA/CMDL-BRW record (red) with coefficients indicated [in brackets] for each of the sites. Notice that there is a trend toward earlier melt dates at most of the sites. The map view of northern Alaska (bottom) shows the approximate locations of the seven sites.
Source: adapted from Stone et al., 2001 and NOAA.