The Earth's oceans will lose 5% of marine animals globally for every degree of warming, even without taking into account the broader impacts of fishing, according to the most comprehensive global study of its kind published in the Proceedings of the National Academy of Sciences (PNAS) on June 11.
With warmer oceans pushing fish toward the cooler poles and larger species suffering the biggest decline, the new report, "Global ensemble projections reveal trophic amplification of ocean biomass declines with climate change," aims to provide the clearest picture yet of how climate breakdown risks the structure and function of our oceans' ecosystems.
While warmer global temperatures have already caused a significant loss and redistribution of the world's sea life, the impacts in Europe will be the most keenly felt, according to one of the report's 35 authors, Boris Worm from Dalhousie University in Halifax, Canada.
DW spoke with Worm about the impact of climate change in the oceans and how we can reverse the trend.
DW: It doesn't come as a surprise that climate change is affecting the oceans. But what's the situation in Europe's seas?
Boris Worm: In Europe we typically don't feel as vulnerable to climate change as, say, people in Bangladesh or in sub-Saharan Africa. But this report shows that Europe is actually among the most vulnerable in terms of climate impacts on marine ecosystems and declines in marine animal biomass.
In various regions of Europe, there has already been a 15-20% reduction in productive capacity and we expect an additional 30% reduction with further warming. The global average masks the fact that the declines we're already seeing, and expect to see in the future, will be much more damaging here than in other ocean basins.
From that perspective, Europe is not shielded in any way from the impacts of climate change on our oceans; we're actually at the forefront of climate change. We can't buy our way out of this.
However, since climate change affects the distribution of fish stocks and species begin to migrate from warmer to cooler areas, could the North Sea benefit from such a migration?
The North Sea is one of the regions that is already seeing, and will further see, declines in productive capacity with climate change. But northern waters, for example in northern Norway, are seeing an increase in total biomass. The available habitat for fish that can live in these very northern waters is expanding right up to the North Pole. So now we have cod spawning just a few degrees shy of the North Pole, where they were never found in the past because the habitat conditions were not suitable for them.
The question is how much are you able to gain from the ocean, and both the historic analysis of the last 70 years and the future forecast show that the total volume of what can live in our waters is decreasing and will further decrease.
And with every step up the food chain, we see a larger effect of climate change. While the effects on plankton may be relatively more moderate, the effects on small fish are much larger, and even larger on larger fish. That's concerning, because a lot of the animals we really care about tend to be large. Think about large bluefin tuna, whales or seabirds.
Climate change is largely to blame, but how does overfishing play into all of this?
The effect of fishing on marine animals' biomass is quite a bit larger than that of climate change, but climate change is going to impact marine animal biomass' whether we're fishing or not.
If both fishing and climate change remain unchecked, we could see an ocean that's much more depleted than we can imagine now. In fact, a lot of the really drastic stock collapses we've seen in the past have often been due to the fact that a stock was not doing well due to an unfavorable environment and was fished very hard at the same time. So if those two pressures come together, we can see fairly drastic and rapid changes that may not be easy to reverse.
And what are the social impacts of such a situation? How would this affect an average person?
The redistribution of fish due to climate change has already sparked conflict, for example with mackerel from the North Sea moving into Icelandic waters. They weren't there before, so they didn't have a quota. As Iceland started to fish a certain quota — which has to be accounted for because it's a zero sum game — other nations could fish that stock less. So, with climate change, the questions about whose fish they are and how much is there for the future are becoming more pressing.
We do have a lot of precedence for what it looks like when oceans become quite empty. For example, in the Philippines, due to unchecked exploitation of coastal waters, people have to pick up sea urchins or any other invertebrates they might find. There are no fish left and something needs to be there for the dinner plate. I've seen it as well off West Africa where foreign overfishing has threatened the livelihoods and food security of coastal nations.
The social consequences can be quite dire. Fish are actually very important for delivering micronutrients that are important for brain development, particularly in children, and there are a lot of countries with no other readily available source.
So what needs to be done to avoid the current situation from worsening?
We can fish more cautiously and let populations rebuild the biomass where they're more resilient, and we can address climate change from the bottom and not let the oceans warm to the degree that they would under business as usual.
It adds emphasis to European leadership in climate negotiation and climate mitigation, and trying to get ahead of this problem and lead the trend toward faster climate action.
It's something we need to do anyways as we're running out of fossil fuels, so if we do it earlier we can avoid some of these deleterious impacts.
But, you know, I'm always hopeful. Humans are good at collaborating. We're a social species, much like killer whales and wolves, and we can work together. That's how we survived in the past and I think that's how we will survive in the future.
Boris Worm is a marine ecologist and Killam Research Professor at Dalhousie University in Halifax, Canada.
This interview has been edited and condensed for clarity.