“Look”, says Aafke Schipper as she moves her cursor over four purple-yellow world maps on the screen. “Here you can see the percentage of fish species that are faced with unprecedented, extreme conditions. The larger the yellow areas, the worse the situation.” You don't have to be an expert to see the difference between the four maps. In the scenario with an average of 1.5 degrees Celsius warming, the world is still mainly purple, with a few yellow areas. But on the maps for 2 degrees, 3.2 degrees and 4.5 degrees of warming, those yellow areas increase in size. On the world map with the 4.5-degree scenario, almost all of South America is bright yellow. “This means that almost all freshwater fish species on the continent will be subjected to conditions that could cause them to become extinct.”
Schipper is an environmental scientist at Radboud University. She conducts research into the habitats of freshwater fish and found that limiting global warming makes a huge difference to these species. And that's good news, not only for animal lovers, but also for ambitious policy makers seeking support for their climate plans. “If we implement all current policy measures and do nothing else, we will get 3.2 degrees of warming. But in our models, you see that the damage to freshwater fish is greatly reduced if we can limit warming to the 1.5 degrees from the Paris Agreement. To be honest, I was surprised about that myself: this lower target really does matter.”
Complete picture
Schipper and her colleagues are the first in the world to conduct large-scale biodiversity research on freshwater fish. “There are many research groups that model the distribution of mammals or birds. But no global models for freshwater fish had yet been developed. We decided to fill that knowledge gap.” The researchers looked not only at the effects of global warming on fish species, but also at the current and future fragmentation their habitats – for example, due to the construction of river dams. To determine the effects, they combined data sets from all over the world to create a model. “There are about 15,000 freshwater fish species. We looked at the data for 11,500 species, which gives a reasonably complete picture.”
Food web
A cynic could say: well, it’s sad when fish species go extinct, but is that really so bad? “This is partly an ethical issue,” says Schipper. “I think a lot of people feel deep down inside that this just shouldn’t happen. It is simply unethical for all kinds of other species to disappear on Earth due to the activities of one species – humans.”
For those who don't like that ethical argument, there are also other drawbacks to a world without freshwater fish. When a species becomes extinct, this often affects the entire ecosystem. “How that works exactly depends on a number of aspects,” says Schipper. “For example, is the species that disappears herbivorous or carnivorous? And how exactly does the food web operate?” If a species of fish that eats other fish disappears, then a species that eats algae can ‘benefit’. In other words, the population of that species will increase. “Then more algae will also be eaten, and the CO2 absorption from the atmosphere will decrease. In this way, the extinction of a certain species can even contribute to climate change.”
The extinction of fish species also has direct consequences for humans. “This is particularly the case for human populations that depend on fishing for their daily food and income. By the way, these are not usually the people who are causing climate change. And that also touches on an another ethical question: can we in the developed world, as the major emitters, pass on the consequences of our lifestyle to others?”
Science in practice
Aafke Schipper (1979) is an assistant professor of environmental science at Radboud University. Her research focuses on how human activity affects biodiversity. Schipper also works as a researcher at the Netherlands Environmental Assessment Agency (PBL), where she makes large-scale biodiversity models. “The great thing about this dual position is that I can immediately put my research at the university into practice at the PBL. The models we make there support global climate and biodiversity policy. To be able to make sound policy, you need to know which actions have the most effect. For example, what is the effect of climate change on biodiversity loss when compared to the effects of land use or pollution? When you know that, you can decide on what to do to prevent the greatest damage.”
Cornered
Part of Schipper's research consists of future scenarios: what are the expected consequences of certain events? But she emphasises that the purple-yellow world maps from her freshwater fish study do not show scenarios for the distant future. 'The earth is already 1.1 degrees warmer on average than it was at the end of the nineteenth century.” Moreover, the average temperature does not say everything. Extreme events such as heat waves, droughts and floods are increasing both in intensity and frequency due to climate change. “And if extreme heat waves only last for one week per year, this can cause local extinctions of some fish species. That is why we used those extremes as a starting point.” This is not a happy story, but Schipper still seems relatively cheerful. She emphasises that it is certainly not too late, but we must take action now – also regarding the fragmentation of habitats. This is the other risk factor that she and her colleague Valerio Barbarossa looked at in their research. “Many fish species are literally cornered because large dams have restricted their habitat. As a result, their populations may become too small to remain viable.”
Difficult dilemma
For freshwater fish, man-made dams are therefore a disaster, even though many new hydroelectric dams will be built in the coming years to generate low-carbon energy. “Due to the climate crisis, we obviously have to make an energy transition. But hydroelectric dams also fragment the habitats of freshwater fish. This shows that well-intentioned interventions can sometimes turn out badly in other respects.”
This is a difficult dilemma, admits Schipper, which is mainly taking place in equatorial regions. “There are many plans for new dams in these regions. In our model you can see that this particularly affects the Amazon region. Regarding the consequences of global warming, the Mediterranean will be severely affected: the freshwater habitats are not only getting warmer, but droughts are expected to occur more often and to last longer.”
Extremes in river discharge can also endanger freshwater fish. “If a lot more water suddenly flows into a river, for example due to extreme rainfall, then fish eggs or larvae can be washed away. And of course, fish suffer in the event of a drought. If the water in their habitat dries up, they have nowhere to go.”
Wicked problem
Solutions to these problems are urgently needed. But where do you start? Biodiversity loss is what scientists call a wicked problem: a problem that is difficult to solve due to all kinds of dependencies. “Because the earth is warming, for example, species are forced to move to new habitats. But they can’t always do this because they encounter human barriers. Alternative energy sources limit warming and thus reduce the need for species to move, but this is often at the expense of their current habitats.” Schipper's team is therefore working on solution-oriented scenario studies. “We include all kinds of possibilities in our calculations. For example, what will happen if we all continue with ‘business as usual’ or what will change if we all reduce consumption and invent smart technology?”
According to Schipper, the outcomes of those scenarios are hopeful and sad at the same time. “It is not too late to save many species from extinction. But that also requires major investment, for example in technological innovations, especially in areas where people do not yet have access to them. At the same time, we have to cut back considerably in consumption – especially in the developed world. Any way we look at it, this means flying less, buying less stuff and eating less meat or different types of meat. For example, it would make a big difference if everyone switched from beef and pork to chicken and insects.”
Schipper understands that is a big challenge for the average Dutch person. “We really need to structure our society differently. The message could also be more positive. Not: if we don't do anything, disaster is imminent. But: if you make a change, you contribute to a better world. In my opinion, the government should not put all responsibility for taking action on individual citizens. You cannot expect everyone to consider sustainability in every decision they make – especially when the sustainable choice is often more expensive. I think that's asking too much.” In the media, the discussion sometimes flares up and focuses on a dilemma: which is worse, biodiversity loss or climate change? “I think it's very difficult to separate those two from each other, precisely because climate change also affects biodiversity. People also tend to confuse ‘nature’ with ‘biodiversity’. We need nature and natural resources, and we also need variety in species. But it is not the case that all species that exist today are essential for the continued existence of humans.”
The problem is that we don't know exactly how much biodiversity is needed, she explains. “If certain freshwater fish species become extinct and we find out later that they were crucial, then we really have a problem.”
Canadian salmon injured by heat wave
This summer, various media (including The Guardian) published a video showing how salmon suffered from the extreme heat waves in Canada. Temperatures in July were as high as 49.5 degrees Celsius in some places. As a result, the water temperature rose to 21 degrees, which is much too warm for salmon. The images show salmon with large lesions and fungus on their skin – a result of stress and overheating. “You can see here that an extreme situation – water temperature that is too high – means that the habitat of the species is in fact no longer suitable, which could endanger the survival of salmon,” explains Schipper. “Whether the fish can recover depends on the level of mortality and how often the extremes occur.”
Follow-up study
Her first research results are now being read around the world, but Schipper is already planning a subsequent study. Besides the two factors – climate change and habitat fragmentation – that her team has been investigating in recent years, the survival of fish species is affected by many additional threats. Follow-up research should identify these additional factors and determine how they relate to each other and how they influence each other. Ideally, she would like to be able to say something about the viability of a particular species. “We have not yet been able to take that step. Ultimately, we want to arrive at a model with a clear final conclusion for policy makers: if you implement a specific policy, then a specific number of species will become extinct. Moreover, if we know how to do this, we can also save a specific number of species.”
Special animal
And what will happen if everything goes wrong? What would a world without freshwater fish look like? Schipper shakes her head. “I think that would be a poorer world. I really believe that. Ultimately, it’s not just about the usefulness of biodiversity or nature, but it’s also about what kind of planet you want to leave behind for your children.” Last year, she says, another fish species was officially declared extinct: the Chinese paddlefish. “That was one of the largest freshwater fish on Earth – you can Google it for fun. Then I think: wow, that was a beautiful, very special animal. It existed for millions of years, long before any humans. And now we have a world in which the Chinese paddlefish is extinct.”
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Text: Susanne Geuze. This article appeared first in Radboud Magazine #69. Photo: Lena Denk via Unsplash