The science of sustainable seafood, explained

MPAs will suffer, along with the rest of the ocean, as the planet warms

A paper (Bruno et al. 2018) released last week in Nature Climate Change mapped the effects of future emissions on marine protected areas (MPAs) around the world. The results were unsurprising—climate change threatens every MPA (and indeed every part of the ocean), with a range of impacts. This study focused mainly on warming temperatures and changing oxygen levels, but anthropogenic stressors on the ocean also include ocean acidification, rising sea levels, more intense storms, distorted currents, and altered nutrient distribution.

To understand the paper, its conclusions, and any kind of positive takeaway (we get there at the end), an understanding of representative concentration pathways (RCP) is needed. An RCP is a scientifically backed estimate of radiative forcing (you can think of this as the amount of global warming) based on different emissions scenarios. Basically, an RCP estimates the amount of warming Earth will experience based on the amount of future emissions. It is important to note that RCPs are not climate models—they are scientifically standardized scenarios that can be used to set up models. The 4 recognized RCPs are: RCP 2.6, 4.5, 6, and 8.5.

Radiative forcing is a measure of the amount of energy trapped in the atmosphere. Greenhouse gasses have the largest forcing effect as they trap radiation (like a greenhouse!), which warms the planet.

In the paper, the authors model RCP 8.5, the worst-case scenario where politicians, governments and people don’t make meaningful change in the future. Predictably, the results are not good. In this scenario, temperatures inside (and outside) MPAs are expected to rise by an average of 0.035° C per year leading to “protected areas” that are at least 2° C (4.6° F) warmer by the end of the century.

Figure 1 from Bruno et al 2018. Patterns of projected ocean warming. Annual warming rates (color scale) are based on CMIP5 simulation ensembles under the RCP8.5 emissions scenario, 2006–2100. Black dots are MPAs used in the study.

Marine animals and ecosystems are already feeling effects from rising temperatures—continued failure to enact meaningful mitigation policies will devastate many living things in the ocean and the people that rely on them for food, income, and livelihood.

The authors also map deoxygenation changes in the ocean. Deoxygenation is the lowering of dissolved oxygen in water due to human-caused factors like rising water temperature—warmer water holds less oxygen and creates stratification issues where warmer, less dense water does not mix with cooler water.

The authors mapped doxygenation changes in concert with temperature changes in an effort to explore oceanic ‘refugia’—or places that could potentially remain within natural variations of temperature and oxygen levels in hopes of establishing MPAs there. The prospects under RCP 8.5 are not promising: under RCP 8.5, only 3.5% of existing MPAs would stay within natural variation of temperature and oxygen (to say nothing of other issues like ocean acidification). Basically, under RCP 8.5, warming water temperature and decreasing oxygen levels will gravely threaten all areas of the ocean, MPA or not.

The paper concludes:

Although MPAs are widely promoted as a means to mitigate the effects of climate change, the opposite perspective is more in line with scientific reality: without drastic reductions in carbon emissions, ocean warming, acidification and oxygen depletion in the twenty-first century will in all likelihood disrupt the composition and functioning of the ecosystems currently protected within the world’s MPAs. The community- and ecosystem-level impacts of climate change threaten to negate decades of progress in conservation and further imperil species and ecosystems that are already in jeopardy.

The authors do make a point to explicitly state their support for MPAs, though I think this paper better supports the premise I have written about before: MPAs are often poor conservation tools as there are better, more impactful policies to advocate for (like reducing emissions!). It may be easy to say that advocates for the ocean should fight for reducing emissions and MPAs, but that approach spreads advocacy too thin; political capital is finite and should be allocated to the most important ocean issues, like reducing emissions and preventing pollution. I expand on those thoughts here.

Inspirational takeaway! (I hope)

Though much of the discussion has focused on RCP 8.5, Bruno et al. 2018 also modeled RCP 4.5, which I would cautiously (and optimistically) call a more plausible future than RCP 8.5. Under RCP 4.5, projected warming in the world’s MPAs (and surrounding ocean) would be 0.015° C per year, much lower than the 0.035° C under RCP 8.5. Though this amount of warming would still be damaging to the ocean and its life, it would be much less devastating than 0.035° C. The important takeaway from these numbers is that reducing emissions counts. Reducing emissions by any amount reduces the corresponding burden on the ocean and increases the chances for more life to persist in the ocean.

Studies like Bruno et al. 2018 can spur feelings of hopelessness and despair, however, I think the paper should remind us that fighting climate change is not hopeless or pointless—the more we reduce emissions, the further we reduce the future burden on the ocean. Yes, the ocean will suffer from climate change, but reducing suffering is important and noble.

On an individual level, the best thing you can do to reduce emissions is watch your diet. Large-scale mitigation will come from policy and institutional change that you have some input on with your vote. Register to vote here.

Picture of Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW.

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