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Environment: understanding atmospheric and ocean flows
Environment: understanding atmospheric and ocean flows

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5 The contemporary Arctic climate

There is a remarkable seasonality in the Arctic climate. For example, the flow in some of the great rivers of Russia and North America that empty into the Arctic Ocean almost stops in winter (Figure 25). During May, ice in the rivers starts to break, and in June there is a rapid flood of fresh water followed by a fall in flow until November, when it freezes.

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Figure 25 The monthly discharge on the Lena River (Russia). Each individual bar in the graph represents a monthly value for each year during 1935–99.
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This is a graph of the discharge from the Lena River in Russia for the each month during 1935–1999. The horizontal axis is month of year from January to December. The vertical axis is monthly discharge from the river in cubic metres per second. The minimum is 0 cubic metres per second, the maximum is 120 000 cubic metres per second, and there are ticks every 20 000 cubic metres per second. In each month there is a series of 64 vertical bars representing the monthly discharge for each year in the period 1935–1999. From January to April there is almost no flow in the Lena and the bars are all less than 5000 cubic metres per second. In May approximately one quarter of the bars are greater than 5000 cubic metres per second, but the maximum discharge is still only around 30 000 cubic metres per second, and this only occurs in perhaps less than ten occasions in the record. In June there is a clear huge pulse in discharge and all of the bars are in the range 60 000–100 000 cubic metres per second. In July the discharge reduces to around 40 000 cubic metres per second, and in August and September it has reduced again to about 20 000 cubic metres per second. In October the discharge is typically about 10 000 cubic metres per second and finally in November and December the discharge is again less than 5000 cubic metres per second.

Figure 25 The monthly discharge on the Lena River (Russia). Each individual bar in the graph represents a monthly value for each year ...

A similar huge seasonal signal is seen in the Arctic sea ice cover (Figure 22). Most people are surprised to realise that the sea ice of the frozen Arctic Ocean is only a few metres thick. Beneath this are a few kilometres of water. In winter as much as 16 million square kilometres of the ocean freezes, and as this melts in summer, only about 6 million square kilometres remains frozen. The seasonal variation of almost 10 million square kilometres is equivalent to about 45 times the area of the United Kingdom.

The contemporary Arctic climate appears to be changing. However, average global temperatures mask regional variations and the Arctic has been warming faster than the global mean (Figure 26).

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Figure 26 The annual average near surface temperature from all weather stations on land relative to the average for 1961–90 for all regions from 60° N to 90° N (AMAP, 2012)
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This is a graph of the average near surface temperature from all land stations from 60° N to 90° N. The horizontal axis is year from 1880 to 2010 and there are ticks every 10 years. The vertical axis is temperature change relative to the 1961–1990 mean in degrees Celsius: the minimum is −2 °C, the maximum is 2.5 °C and there are ticks every 0.5 °C. The zero on the vertical axis is the average temperature for 1961–1990 for all regions from 60° N to 90° N. There are blue dots representing the average temperature for each year. From 1900 to 1920 the points are all below 0 °C, from 1920 to 1960 almost all points are above zero, from 1960 to 1980 almost all points are below zero, and finally, from about 1980 to 2010 the points are mostly above zero and follow an upward trend.

Figure 26 The annual average near surface temperature from all weather stations on land relative to the average for 1961–90 for all ...

Activity 11 Recent climate change in the Arctic

Timing: Allow about 10 minutes

Describe the changes in Arctic temperature that are shown in Figure 26.

Discussion

With the exception of a period in the 1960s and 1970s, the Arctic land temperature has been above the 1961–90 average in most years since 1920 and reached 2 °C above the 1961–90 average in the early part of the 21st century. These data came from the Arctic Monitoring and Assessment Programme. They appear to use the latitude of 60° N as their definition of the Arctic, so Figure 26 must include meteorological stations that are not in the Arctic as it has been defined in the course, which are less likely to be affected directly by changing ice and snow cover. For this reason, Figure 26 most likely underestimates the land temperature increase.

Next you will look at the impact of land temperature increases.