Page 169 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 5 global Temperatures 133
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▲Figure 5.15 July average temperatures for polar regions. July temperatures in Celsius for (a) north polar region and (b) south polar region. note that each map is at a different scale. [adapted by author and redrawn from national Climatic Data Center, Monthly Climatic Data for the World, 47 (January 1994), and WMO and nOaa.]
Amundsen–Scott Station at the South Pole (elevation 2835 m); and –32°C at the Russian Vostok Station (elevation 3420 m), the most continental location of the three.
Figure 5.15 maps July average temperatures in the north and south polar regions. July is “summer” in the Arctic Ocean (Figure 5.15a), where rising air and ocean temperatures are causing sea-ice melting, as discussed in the Chapter 4 Geosystems Now. Open cracks and water channels through ice, or “leads,” stretched all the way to the North Pole over the past several years.
In July, nights in Antarctica are 24 hours long. This lack of insolation results in the lowest natural temper- atures reported on Earth; the record is a frigid –89.2°C recorded on July 21, 1983, at the Russian Vostok Station. This temperature is 11 C° colder than the freezing point of dry ice (solid carbon dioxide). If the concentration of carbon dioxide were large enough, such a cold tem- perature would theoretically freeze tiny carbon dioxide dry-ice particles out of the sky.
The average July temperature around the Vostok Station is –68°C. For comparison, average tempera- tures are –60°C and –26°C at the Amundsen–Scott and McMurdo Stations, respectively (Figure 5.15b). Note that the coldest temperatures in Antarctica are usually in August, not July, at the end of the long polar night just before the equinox sunrise in September.
annual Temperature Range Map
The largest average annual temperature ranges occur at subpolar locations within the continental interiors of North America and Asia (Figure 5.16), where average ranges of 64 C° are recorded (see the dark brown area on the map). Smaller temperature ranges in the South- ern Hemisphere indicate less seasonal temperature variation owing to the lack of large landmasses and the vast expanses of water to moderate temperature extremes. Thus, continental effects dominate in the
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Georeport 5.3 Polar Regions Show Greatest Rates of warming
Climate change is affecting the higher latitudes at a pace exceeding that in the middle and lower latitudes. Since 1978, warming has increased in the arctic region to a rate of 1.2 C° per decade, which means the last 20 years warmed at
nearly seven times the rate of the last 100 years. Since 1970, nearly 60% of the arctic sea ice has disappeared in response to in- creasing air and ocean temperatures, with record low levels of ice since 2007. The term Arctic amplification refers to the tendency for far northern latitudes to experience enhanced warming relative to the rest of the northern Hemisphere. This phenomenon is related to the presence of snow and ice, and the positive feedback loops triggered by snow and ice melt, as discussed in previous chapters (review Figure 1.8 and Geosystems Now 4). Similar warming trends are affecting the antarctic Peninsula and the West antarctic ice Sheet, as ice shelves collapse and retreat along the coast.
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