2025 has been an extraordinary summer. I went south to the London area to visit friends and family, and I have never experienced such conditions since I was working in Greece and the Middle East fifty years ago. Temperatures were over 30 degrees C. Everywhere I went, green lawns were burnt to a crisp, and we had to carry water bottles, and stay indoors during the midday hours. The effects of global warming have become starkly clear. Orkney hasn’t been so badly affected, but we have still had long periods when temperatures were over 20 degrees C and our gardens needed a lot of watering. So am I going to start planting olives and lavender? I don’t think so. Because global warming may well affect the Gulf Stream, which is a major factor in the Scottish climate.

The Gulf Stream is a warm surface current which flows from the Gulf of Mexico, up the east coast of America, to the North Atlantic and Northwest Europe. The north-eastern extension of the Gulf Stream is known as the North Atlantic Current, the North Atlantic Drift or the North Atlantic Sea Movement. It is this part of the Gulf Stream which reaches Britain. The warmth it brings keeps temperatures in NW Europe higher than they would otherwise be at these latitudes.  It is the reason why palm trees will grow on the west coast of Scotland at places like Inverewe in Wester Ross, and why Orkney, at latitude 59 degrees north, has a cool mild climate rather than a cold one.

The density of the water is important as well as its warmth. This depends on its salinity as well as its temperature. When it reaches the Arctic, the water of the Gulf Stream has cooled and become saltier, so it sinks below the surface and flows south again as a cooler deep-water current. This circulation around the Atlantic is known as the Atlantic Meridional Overturning Circulation or AMOC. Global warming means that not only is the ocean warming up, but the Arctic and Greenland ice sheets are melting, releasing huge amounts of fresh water into the ocean and reducing the salinity of the northern Atlantic. The AMOC is already slowing down and eventually is likely to slow down significantly even if it does not stop entirely. If this happens, NW Europe, including the whole of Britain, may well become colder and stormier, although it is also argued that the effect of general global warming may to some extent compensate for this. There appear to be different estimates of how much colder and how soon this is likely to happen. But it could happen relatively quickly.

It has happened before. At the end of the last Ice Age, the planet was gradually warming up. But from around 12,500 until 11,500 years ago, i.e. a period of about 1,000 years, there was an abrupt return to very cold conditions in the Northern Hemisphere. The Southern Hemisphere grew warmer at the same time. Within a few decades the annual air temperatures in Europe dropped by 2-6 degrees centigrade, mainly in the winter. This cold period is known as the Younger Dryas, named after the flower ‘Dryas octopetala’ which flourishes in these conditions. Various causes have been suggested. These include a meteor impact, but it is considered more likely that it was the effect of a large amount of fresh water suddenly entering the North Atlantic as the ice in North America melted. This altered the salinity of the ocean, slowing down the currents which transport heat from the South to the North Atlantic.

Orkney currently has a temperate oceanic climate, with mild winters, very little snow, short cool summers, strong winds and comparatively high rainfall all year round. Both cereals and vegetables grow well in Orkney, although cereal crops are at risk from the short growing season and from damage by the strong winds. Bere barley and oats are the traditional grains. The various islands in the Orkney archipelago differ slightly in what does best.  Low said in the late 18^th century of South Ronaldsay: “The corns of this island are generally late in ripening, and the crop rather precarious when the season proves broken and the harvest rainy; however this is not so much the case but this furnishes vast quantities of meal and malt even in years when many of the other isles are but poorly off in this respect, so that in general they can spare more grain than any other of the S. Isles in proportion to the bulk of their island and extent of arable land.” (Low 1774 pages 24-25). In the past, Orkney and Shetland traded extensively with Norway, exchanging grain and malt for timber.

The Old Statistical Account, also compiled in the 18^th century, records much the same vegetables as today growing in Orkney:   “…in the account for the parish of Birsay and Harray, Orkney: ‘The gardens will produce early cabbage and colliflower; as also onions, leeks, garlick, parsnips, carrots, turnips, and small salad herbs…’ This minister is probably writing about his own garden.”(Maisie Steven 1995 page 37); while Low remarks that “… in no place do potatoes thrive better than here [South Ronaldsay], ” (Low 1774 page 49-50).

If the Gulf Stream does shut down completely because of global warming, Orkney may end up with a different kind of climate, at worst subarctic/boreal (Dfc), similar to present-day Tromso in north Norway, which lies at 69 degrees north, i.e. 350 km north of the Arctic Circle. In other words, things would get significantly colder in these latitudes, perhaps up to 5 degrees colder, especially in winter.

That’s not to say we won’t be able to grow anything without a solar-powered greenhouse. I have stated my concerns about hi-tech indoor gardening in a politically unstable world elsewhere. Overpopulation, as well as the climate crisis, means that there certainly won’t be enough agricultural land available to feed everyone, so things like vertical farms will have to be tried. But it would probably be a good idea to grow as much food as we can without the help of technology. Fortunately, that seems to be possible. The Financial Times published an article on ‘Arctic Gardening’ in November 2024. Their photo of a woman with handfuls of carrots, standing against a background of abundant cabbage and parsley, grown in the Lofoten Islands (Norway, 68-69 degrees north) was impressive. This woman mentions growing kale, pak choi, green beans, parsnips and strawberries. She recommends sowing outdoors so that the plants have an opportunity to adapt to outdoor conditions. Another contributor recommends growing perennials because their root system is already established when the short growing season starts. The usual techniques are mentioned: drainage, planting windbreaks and using south-facing exposures. Potatoes were mentioned later on. Barley will grow in these regions although the short growing season is a problem.

So it can be done. But thinking ahead, a greenhouse might be a better investment in Orkney than a grapevine…

“A Tour thro’ Orkney and Schetland in 1774”, George Low

“Parish Life in Eighteenth-Century Scotland: A Review of the Old Statistical Account”, Maisie Steven 1995