The Arctic Ice Cap is Shrinking!

Microwaves – electromagnetic radiation with short wavelengths – are utilized in many households to heat foodstuffs. But these waves also have other, more exotic applications. Since 1978, satellites have been bombarding the earth's surface with microwaves from space! These satellites are equipped with radar instrumentation that daily monitor the intensity of microwave reflection off the planet's surface.

Figure 1:A microwave map showing the Arctic ice cap.

These microwave records provide an extraordinary amount of information. Microwaves are modified by the nature of the matter that they encounter – its density, particle shape and size for example. The microwaves detected by satellite radar differ depending on whether they bounced off solid ground, water, ice, or snow. With the microwave data, scientists create maps, with varying intensities of the microwaves indicated by varying brightness of the image (Figure 1).

Microwave monitoring has recently been applied to survey the Arctic ice cover1. By analyzing the data over the past two decades, it has been possible to detect changes in the extent of ice cover over the years, as well as between seasons (Figure 2). Even differences in the depth of ice cover have been quantified! The results have been enlightening–perhaps even frightening. Since 1978 there has been a 14% reduction in the winter ice cover in the arctic. This represents a decrease of about 31,000 km2 of "permanent" (year-round) winter ice a year. These losses reflect a 5 day increase in the length of the ice melt season.

Figure 2: This graph depicts the decrease in polar ice area since 1978.

In an independent study, submarine sonar data indicated that the fluctuations in the area of ice cover since 1978 are in very close agreement with estimates of ice thickness. The association is an important one; the loss of ice cover is not merely due to peripheral changes, but instead reflects a substantial loss of ice mass throughout the polar ice sheet. The Arctic is melting!

The decreases have been more pronounced from 1987, in conjunction with atmospheric circulation changes. The disappearance of large quantities of ice has the potential to further affect global climate, through an effect on atmospheric circulation. At this point, it is impossible to determine whether the changes are part of regular fluctuations occurring on a scale of decades or part of a more long-term change in global climate. If the trend continues, the shrinking of the polar ice caps will certainly be associated with some drastic changes, in both climate and sea levels. Oceanographic studies have revealed a substantial increase in the amount of water in northern oceans during the last two decades. Perhaps today's children will one day live in a world devoid of polar ice caps, polar bears, and icebergs!

1 Johannessen OM, Shalina EV, Miles MW. 1999. Satellite evidence for an Arctic sea ice cover in transformation. Science 286: 1937–1939.