A1

i—>—i—1—i—'—\—i—\—1—i—•—i—'—i—'—i—1 1900 1920 1940 1960 1980 2000 2020 2040 2060

Year

Figure 6.1. Changes in the anomaly of mean annual air temperature in the 70oN-85oN zone during 1900-2007 (solid line), and its background forecast (dotted line).

a "60-year" cycle, a linear trend in the second half of the twentieth century, and a "20-year cycle" for the seas of the western region. For updating the average duration, amplitude, and initial phase of the "60-year" cycle, harmonic processing of the polynomial trend ordinates of total ice extent was implemented separately for the western and eastern seas. Amplitudes used for the western and eastern seas were 210 ■ 103 km2 and 70 ■ 103 km2 respectively.

As shown in Figure 6.2, it is predicted that in the twenty-first century, oscillatory (rather than unidirectional) ice extent changes in the Arctic Seas will continue. During the 2020s-2040s, an increase in ice extent is projected, with a maximum around 2030 in the eastern seas and around 2035 in the western seas. The next maximum falls at approximately 2090-2095 (Karklin et al., 2001; Gudkovich et al., 2002b, 2005).

An important factor for shipping conditions in the Arctic Seas is the duration of the period that allows unescorted navigation. Table 6.1 shows average durations of through voyages without icebreaking escort along the NSR (from the Kara Sea to the Chukchi Sea), with the average varying from 0 to 35 days.

During the periods of increased ice extent (1962-1983), icebreaker escorts were needed for 50% of cruises along the NSR in order to provide through voyages, while in periods of decreased ice extent (1933-1961 and 1984-2004), icebreaker escorts were required in only 17% and 14% of voyages, respectively.

L, 1000 km2

Yeat

L, 1000 Km2

Figure 6.2. Forecast of climatic changes for the total area of ice extent in the western (a) and eastern (b) Eurasian Arctic Seas for the twenty-first century, taking into account the linear trend in the second half of the twentieth century.

Table 6.1. Average duration of unescorted through navigation along the NSR (depending on the total ice extent of the Arctic Seas).

Total ice extent gradations (%)

Average duration of through voyage without icebreaker support (days)

>12

0

+2 to +11

9

-4 to +1

13

-9 to -5

26

< -10

35

Figure 6.2. Forecast of climatic changes for the total area of ice extent in the western (a) and eastern (b) Eurasian Arctic Seas for the twenty-first century, taking into account the linear trend in the second half of the twentieth century.

Year

Figure 6.3. Number of periods of unescorted through navigation for the Russian ice-strengthened (UL') ice class ships along the NSR (10-day periods)

Year

Figure 6.3. Number of periods of unescorted through navigation for the Russian ice-strengthened (UL') ice class ships along the NSR (10-day periods)

This is confirmed by actual data on the duration of periods of unescorted through voyages along the NSR for 1940-2000, as shown in Figure 6.3; even during the last period of Arctic warming, there were years when unescorted through navigation was impossible. Thus, ice conditions expected at least during the first half of the twenty-first century suggest a continuing need for icebreaker support of marine operations in the Arctic.

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