Dag O. Hessen (Norwegian, born 1956) is a professor of biology. He has published a large number of scientific papers about evolution and ecology, including climate-change issues. He has also published several popular science books and papers and is active in the public climate-change debate.
The key actors in this story are small, typically just a few millimetres. In fact, planktonic Calanus (relatives of crabs and lobsters) remind us that the big players are not always large in size. But in the Arctic seas, Calanus are large in numbers, and they play a vital role. They are among the noble group of organisms that definitely earn the title keystone species. And understanding what could happen to Calanus as Arctic waters warm tells us much about the future of life in high-latitude seas.
Ecological and economic systems share several properties, including the fact that predicting their future is difficult because everything in them depends on everything else. They are both characterised by multiple interacting feedback loops—cause-and-effect cycles that now and then produce counterintuitive responses. Sometimes, change is gradual. At other times, seemingly small impacts can trigger a big reaction and possibly set in swing irreversible large-scale change.
By 2052 the northern marine waters will be in the midst of such a transition period, and no one can really tell how far it will go. This is partly due to the nonlinearity of biological systems, meaning that the ecosystem response to a given change (like temperature) may not be gradual and simple to predict.
Beyond certain points or thresholds, there may be sudden, dramatic, and apparently random changes due to species shifts or shifts in key ecological processes with cascading effects on the entire system. Part of this is due to the fact that a food web is exactly that—a web. For example, species B may very well tolerate elevated temperatures, but if its prey A does not, B may suffer a heat induced collapse due to loss of A—possibly with cascading effects to species C, D, E, and more.
Or consider the other potential feedbacks of an oceanic temperature rise: increased heat absorption due to reduced snow and ice cover, permafrost melt with subsequent release of CO2 and CH4, ocean acidification causing reduced biological fixation of CO2, and so on. I really don´t know where this will take us, but from 2052 and on it will be terra incognita—or rather mare incognitum.
I do know, though, that by 2052 the temperature in the North Sea will most likely be on average 1.5oC higher than today. Surface water in summer may be elevated by more than 2oC. The same trend will go on all the way up to the Arctic Ocean, which by 2052 will be completely devoid of ice during summer, with higher summer temperatures to match. So why will Calanus—our phytoplankton-eating copepods— and its fellows suffer when the cold northern waters heat up to what would seem more pleasant temperatures? Do not high temperature go along with high productivity?
Not necessarily. First of all, some species simply do best at low temperatures because they are evolutionarily adapted to them. But, secondly, elevated temperatures have some surprising side effects on phytoplankton. We expect that the productivity and average size of phytoplankton will decrease substantially when the ocean warms.
This is at least partly because the nutrient-poor surface water will heat up more rapidly, making it less able to mix easily with the nutrient-rich deep waters that contain phytoplankton. And so higher temperatures mean less food for Calanus—because there will be less phytoplankton mixed into surface water where the copepods feed. It also means smaller food, partly because smaller species do better than larger ones under strong nutrient limitation, but also because cells tend to get smaller at elevated temperatures. Oh sure, Calanus may be small, but the algae are even smaller, and smaller algae mean less of a mouthful for Calanus.
Perhaps even worse, these Arctic waters will by 2052 also experience a drop in pH from a historically very stable level of around 8.2 to 7.9. This is not a trivial change. We will see that crustaceans like Calanus and other calcifying organisms, both plants and animals, start to suffer since they have a hard time constructing their exoskeletons.
But let’s not be to Calanocentric. The Arctic warming will by 2052 affect the entire system via cascading effects. New species will appear. Not only new species of copepods and algae, but also new fish species. Cod, mackerel, and herring typically found there will move northward. A wide range of bottom-dwelling flora and fauna will invade from the south, partly replacing old inhabitants. Some for the better, presumably, but many for the worse. Jellyfish of various kinds will proliferate at the expense of fish. And then I almost forgot the birds. You probably won’t see auks and puffins hatch on the west coast of Norway. By 2052 they will be gone, moved to more northern areas.
One would perhaps have expected that when the ice retreats over the polar sea, it would open up vast new areas not only for oil and gas exploration, but also for marine productivity. Well, I am afraid that this optimistic idea is naïve. First of all, the very deep oceans are not at all as productive as the more shallow and coastal upwelling areas.
Second, the peculiar under-ice ecosystem that is an important part of this high-arctic marine ecosystem will have vanished. During the polar spring you now find green carpets under the ice floes. These are ice algae, rich in polyunsaturated fatty acids and very nutritious.
Relatives of our Calanus time their reproductive peak to graze on these under-ice meadows. But when the ice starts to melt earlier in the year, there will be an increasing mismatch in blooming periods and reproductive efforts of our Calanus. And scarcity of Calanus means scarcity in a key food for fish—affecting seabirds, seals, polar bears, and others. The cascading effect again. By 2052 there will be only faint remains of this quite remarkable food web.
More news awaits, though, for the second half of the twenty-first century when the increased meltdown of the Greenland ice sheet will cause other unpleasantries. The Gulf Stream conveyer belt is to a large extent driven by salinity gradient caused by the density differences of fresh and more salty waters. If the freshwater input disrupts this circulation after 2052, I would say: “You haven’t seen anything yet.”
If fate fares me well, I will be able to witness the world by 2052 as a very old man, but it will give me no pleasure on my last days to realize that I, along with numerous other scientists, were right when we vocalized these worries long before the year 2000. I am a biologist, and the trajectories humanity has followed over the past twenty-five years, despite very clear warnings, makes me wonder about human rationality. To be more precise, I wonder about the apparent victory of our selfish, evolutionarily short-sighted reasoning that maximises personal goods at present over the intellectual or moral rationality that would have been able to avoid the crisis.
Luckily, I can end on a more positive note. We will not, at least by 2052, experience an ecosystem collapse (a popular term that I actually dislike, as ecosystems can change radically and in unpleasant ways, but do not collapse). This globe has been through terrible bottlenecks before and life has always found its way, but clearly at the expense of most of the existing forms of life. Apparently there will always be bacteria, algae, and even cockroaches around. I believe the Calanus species will survive in some habitat or other, and humans are rather robust too. My real worry is the self-reinforcing feedbacks—they are probably already starting to kick in. By 2052 I am sure that even the most wholehearted optimist will realize that humanity is facing a serious challenge, but I also believe that we will still be socially, technologically, and psychologically locked into “business as usual”—the old paradigm.
Thus I may feel lucky in 2052 that my time on Earth soon will be over—but seeing my great-grandchildren playing in the yard, that will give me little comfort.