The Sea Ice Years
By Paul Homewood
As promised, there is a batch of scientific studies here which look at temperature trends in Iceland and Greenland, and in particular at the abrupt end of the warm period, that began in the 1920’s, and the onset of the sea ice years.
1) Hanna et al – An Analysis of Icelandic Climate since the 19thC”
The paper gives this graph of temperatures for Reykjavik, Stykkisholmur and Teigarhorn, from 1873 to 2002. The abrupt change to colder conditions in the 1960’s is clear.
They go on to make some extremely relevant comments:-
- The warming was non-uniform in time, occurring in three distinct phases, approximately from 1880 to 1900, from 1925 to 1940, and from 1983 to 2001. Warming was most rapid in 1919–33, reaching the maximum temperatures over the entire record in 1939 and 1941. The northwestern European records surveyed do not indicate any significant trends over the 1901–30 standard period, whereas Icelandic trends are highly significant , somewhat indicating a decoupling between the Icelandic and northwestern European climates.
- The 1990s was definitely not the warmest decade of the 20th century in Iceland, in contrast to the Northern Hemisphere land average (Houghton et al., 2001). It was cooler than the 1930s by 0.45 °C for Reykjavik, 0.41 °C for Stykkisholmur and 0.16 °C for Teigarhorn.
- In an analysis of Greenland temperature records, Box (2002) lists 1939 and 1941 among the five warmest years and 1907 and 1983 among the five coldest years for the nearest site to Iceland, Tasiilaq, southeast Greenland. This is consistent with the results from Reykjavik (Table IV). Furthermore, this is consistent with the often-cited temperature dipole between Greenland and northwestern Europe (e.g. Van Loon and Rogers, 1978). Thus, 1941 was one of the coldest years of the 20th century in northwestern Europe, e.g. Copenhagen, Oslo, Stockholm (Table IV). 1983 was the 11th warmest year in Copenhagen, 13th warmest year in Oslo, and 18th warmest in Stockholm.
- The Icelandic cooling from the 1940s to the 1980s is in broad agreement with a general cooling between the late 1950s and the 1990s observed in western and southern Greenland (Przybylak, 2000; Box, 2002; Hanna and Cappelen, 2003) and also agrees with the P.D. Jones/Hadley Centre data shown in Serreze et al. (2000) of a widespread cooling (or at least muted warming) over southern Greenland, Iceland and the northwestern North Atlantic. These regions experienced a prolonged and deeper mid-20th century cooling when compared with the global warming trend (e.g. Houghton et al., 2001). The contrast is attributable to variations in the intensity of the Icelandic low and is thus linked to the NAO.
So we know that :-
- The patterns of warming and cooling in Iceland were not always well correlated with similar changes in NW Europe, indeed often the opposite. This automatically renders any attempt to homogenise Icelandic temperature data with stations hundreds of miles away in NW Europe utterly meaningless.
- The sudden cooling in the late 1960’s in Iceland was part of a much wider phenomenon, and certainly applied to Greenland, where similar GHCN adjustments have been inflicted.
2) The Great Salinity Anomaly 1968-82
The second paper, “One Hundred Years in the Norwegian Sea”, by Bob Dickson & Svein Osterhus, looks at events further east, towards the coast of Norway.
They discuss six major six events “that have made an impact on the physical environment of the Norwegian Sea on a timescale of decades, each seeming to involve a different mix of ocean-climate processes, and each therefore providing new insight into the varied nature of physical change and ecosystem response:
1) the Great Chill, 1900 -1920;
2) the Warming in the North, 1920 -1960;
3) the Great Salinity Anomaly, 1968 -1982;
4) the Warming of the Abyss, 1970 present day;
5) the freshening of the subarctic seas; and
6) the warming of the Arctic”
They have this to say about the great Salinity Anomaly.
During winters of the 1960s the leading mode of wintertime atmospheric pressure variability in the sector under discussion, the North Atlantic Oscillation (NAO), evolved to its extreme low index state in an instrumental atmospheric record of over a century’s duration (Hurrell 1995; Hoerling et al. 2001), and possibly much longer (e.g. Cook et al. 2002; Luterbacher et al. 2002). With anomalously high pressure persistently dominant over Greenland, a record northerly airflow swept the Norwegian Sea/Greenland Sea bringing an increasing proportion of polar water south to the seas north of Iceland in a swollen East Greenland Current. The East Icelandic Current, which had been an ice-free Arctic current in 1948-1963, became a polar current in 1965-1971, transporting drift ice and preserving it (Malmberg 1969). Aided by active ice formation in these polar conditions, the Oceanic Polar Front spread far to the south-east of normal, with sea ice extending to the north and east coasts of Iceland.
This large increase in the southward transport of ice and freshwater by the East Greenland Current, preserved by the suppression of winter convection north of Iceland, passed out to the open Atlantic through Denmark Strait in the late 1960s, and was traceable thereafter as the ‘Great Salinity Anomaly’ (GSA) around the subpolar gyre for over 14 years until its return to the Greenland Sea in 1981-1982 (Fig. 10) (Dickson et al. 1998).
They go on to say.
However, the GSA is certainly one of the most dramatic events of the century in the Norwegian Sea.
Ecologically too, the GSA was a quite exceptional event. Jakobsson (1992) concluded that ‘the ‘‘Great Salinity Anomaly’’ has probably generated more variability in fisheries during the last quarter of a century than any other hydrographic event in recent years’. During its passage, Cushing (1995) found a significant reduction in recruitment in 11 out of 15 deepwater fish stocks examined. Further, as its harsh conditions closed down the ‘warming in the North’, they also established a ‘veritable desert’ for Calanus finmarchicus [that herring feed on] in waters north of Iceland (Dragesund et al. 1980; Jakobsson 1980), and set in train a change in the migration pattern of Norwegian spring spawning herring in the Nordic Seas that has taken 35 years to unfold (Vilhja´lmsson 1997; Holst et al. 2004).
So we learn again that this event affected a much wider area than Iceland itself, and that it had major consequences for the region.
3) Lawrence Hamilton
“Sea Changes Ashore: The Ocean and Iceland’s Herring Capital” by Lawrence Hamilton is a history of Iceland’s herring industry, and in particular the fishing village of Siglufjordur, regarded as Iceland’s “herring capital”. The years after the Second World War were a boom time for the herring industry, but then, as the paper describes:-
In the mid-1960s, large-scale physical changes took place in the seas north of Iceland. These physical changes had ecological consequences that led to the loss of the herring’s main food supply.
The authors then go on to refer to the same events as Dickson & Osterhus:-
In the mid-1960s, northwesterly winds associated with a prolonged negative NAO/AO state drove unusual volumes of polar surface water and ice through Fram Strait into the Greenland and Iceland seas.
Dickson et al. (1988:103) described this as “one of the most persistent and extreme variations in global ocean climate yet observed in this century.”
They also include a graph of temperature trends for the north of Iceland, commenting “Figure 6 illustrates the pronounced dip in salinity, sea temperature, and air temperature that marked GSA’70s and the general cooling of north Iceland climate in the second half of the 1960s. The Siglunes section (66°16′ N, 18°50′ W to 68°00′ N, 18°50′ W; see Fig. 5) is a standard oceanographic section north of Siglufjördur, often used to assess climate on the shelf (e.g., Malmberg and Jónsson, 1997). Also shown are annual air temperatures from the northeast Iceland village of Raufarhöfn. Among the available long-term air temperature records, those of Raufarhöfn best reflect climate over the ocean north of Iceland because of the village’s exposed coastal location (66°27′ N, 15°56′ W).”
The air and water temperature records show a similar pattern. From 1920 until 1965, relatively warm conditions prevailed over the northern North Atlantic. In 1965, a sudden change occurred; drift ice and polar water covered the north Icelandic shelf during spring. The following years until 1971 were generally cold, with sea ice and polar water frequently visiting the shores. Warmer conditions subsequently returned, but climate variability also became greater and the average salinity remained below earlier levels. Since 1997 the flow of Atlantic water to the north Icelandic shelf has increased, making salinity levels almost as high as they were prior to 1965 (Jónsson and Briem, 2003). The late-1960s episode of cold air temperatures and cold, low-salinity water, marking the passage of GSA’70s, had ecological and human consequences.
The paper offers us a reminiscence of someone who lived through these times.
In the winter of ’67–’68 I remember watching the sea ice filling the fjord. I slept in a bed by the window in their bedroom, facing the sea, and every morning I would wake up, look out of the window and ask if the ice had not disappeared yet. No one liked the ice. Many had terrible experience of the ice years earlier in their lives with cold, isolation, and even starvation. The creaky sound of the blocks rubbing together and the icy, stale air that surrounded the seaside still remain a vague childhood memory in my head. (Eastfjords native recalling the last year of the herring adventure)
The idea that these abrupt changes never took place is frankly ludicrous.
1) Hanna et al
2) One Hundred Years in the Norwegian Sea
3) Lawrence Hamilton