World Economic Forum

By: Kelly Firth on December 8, 2018

According to a 2016 report, plastics in the ocean could outweigh fish by 2050. However, estimates of the amount of fish in the ocean and projections about the amount of plastics leaking into the ocean are very uncertain.

Last month, federal and provincial environment ministers approved in principle a Canada-wide strategy on zero plastic waste. They set a goal of reducing garbage output by 50 per cent by 2040. On the same day, Catherine McKenna, federal minister of environment and climate change, shared the news on twitter, adding, “if we don’t act, plastics will outweigh fish in our oceans by 2050.”

In this check, we look into the source of McKenna’s claim and consider its accuracy.

Where does the plastics vs. fish comparison come from?

Environment and Climate Change Canada spokesperson Veronica Petro pointed to a 2016 report as the source. The report, The New Plastics Economy: Rethinking the future of plastics, comes from the Ellen MacArthur Foundation, the World Economic Forum, and McKinsey & Company.

According to authors’ analysis, “without significant action, there may be more plastic than fish in the ocean, by weight, by 2050.”

While McKenna’s statement may have overstated the report’s conclusion (she uses the language “will” instead of “may”), it’s based on reputable scientific estimates. A news release from Environment and Climate Change Canada published on the same day as McKenna’s tweet used more accurate language: “Plastics in our oceans could weigh more than fish by 2050.”

Report methodology

The authors of The New Plastics Economy break down their plastics vs. fish comparison in a backgrounder. Their analysis builds on research on plastics stocks and flows into the ocean, assessments of global fish stocks, and projected GDP growth rates.

Using these inputs, the authors conclude, “there could be – in a business-as-usual scenario – plastics stocks in the ocean of about 850-950 million tonnes by 2050, versus fish stocks of 812-899 million tonnes.” They used the lower end of both these ranges (850 million tonnes of plastics and 812 million tonnes of fish biomass by 2050) for The New Plastics Economy headline figures.

Ocean plastics

The authors’ plastics estimate (850-950 million tonnes by 2050) is based on an assessment of the current amount of plastics in the ocean found in a report by Ocean Conservancy and the McKinsley Centre for Business and Environment (2015), research on rates of land-based plastic waste entering the ocean by Jambeck et al. (2015), and long-term GDP growth predictions from the International Energy Agency (2015). The final estimate of ocean plastics in The New Plastics Economy is presented as a range because it takes into account different growth rates of plastic flows into the ocean.

The authors make several assumptions and simplifications in their analysis. For example, because academic estimates of the annual growth in leakage flows of plastics into the ocean don’t extend beyond 2025, they apply GDP growth estimates to the flow of plastics into the ocean from 2025-2050.

The authors write that they are “confident this 2050 forecast relies on overall conservative assumptions.”

Ocean fish stocks

The report estimates the total weight of fish in the ocean, or global marine fish biomass, is 812-899 million tonnes. It conservatively assumes that fish biomass will remain constant between 2015 and 2050.

The report backgrounder says this estimate comes from research by Simon Jennings and co-authors (Jennings et al., 2008), and from research by Ocean Conservancy, a non-profit, for its above-mentioned 2015 report. The authors explain that the lower range corresponds to an estimate of what most people would consider as “fish,” while the upper range also includes the estimated biomass of sharks and rays. Neither estimate includes non-fish marine animals like whales, dolphins, or shellfish. The authors acknowledge the uncertainty of their estimate. In the backgrounder, they write, “the assessment of total global fish biomass is inherently uncertain. Other estimates exist, and there is scope for refinement in future research.”

We reached out to Simon Jennings, lead author of the 2008 report on which the estimate of 812-899 million tonnes is based. Jennings confirmed that estimates of global marine fish biomass are very uncertain. He also said his 2008 estimate was “at the low end of the range of published estimates.” He published a subsequent estimate in 2015 of 4.9 billion tonnes, noting that “the range of uncertainty around this is still very high and there are lots of simplifying assumptions made in these models.”

Other academics have also produced higher estimates of global marine fish biomass than The New Plastics Economy. For example, Villy Christensen, a UBC professor specializing in ecosystem modelling, co-authored a study in 2009 that estimated global fish biomass is closer to 2,500 million tonnes – or roughly 2.5 times Jennings’ estimate. If the fish v. plastics comparison was based on Christensen’s figure, then plastics wouldn’t outweigh fish in the ocean by 2050.

Verdict

Clearly, estimating the amount of fish in the ocean is difficult. Experts have produced a wide range of numbers. About his estimate of fish biomass, Christensen told us, “bottom line, the fish estimate that McKenna used is supported by literature [the Jennings study], and as such I wouldn’t fault her for making the claim, even if my estimate was higher.”

McKenna’s claim that “plastics will outweigh fish in our oceans by 2050” comes from a 2016 report The New Plastics Economy. Her claim is true to the extent that it’s supported by some reputable scientific estimates. However, there’s a lot of uncertainty in the underlying estimates because of how they were reached.

Does the plastics vs. fish comparison matter?

While the comparison between the amount of fish and plastics in our oceans may be attention-grabbing, Jennings pointed out that it’s not a very informative comparison because it doesn’t speak to the impact of so much plastic.

He said, “the important question is about the effects of current and projected levels of plastic pollution on the environment.” These effects, he said, should “determine the resources to be committed to reducing plastic inputs or removing existing plastic.”

See how we score.