Debunking the claim that there will be more plastic in the ocean than fish by 2050

In my last post I wrote On the proposed Canadian plastics bans – Part 1: How the Government created useful “facts” for its scary headlines and how “facts” are being created, essentially out of thin air, to be used as activist talking points. The fight against plastics is a particularly fertile field for the development of these fascinating “facts”. Today I want to write about another “fact” being used by activists that “unless something changes there will be more plastic than fish in the ocean by 2050.”

I was reminded of this topic by a newspaper story with the unsurprising title: Unless something changes, there will be more plastic than fish in the oceans by 2050. While compelling, does this “fact” make sense? No more than the claim that plastics don’t degrade in seawater or that plastics take millennia to break down. What parent hasn’t given their child a plastic outdoor toy and found it sun-bleached and degraded after a single summer outside? The reality is that plastic decomposes in some conditions and doesn’t in others. I think we all agree that paper decomposes when exposed to sunlight and water and yet they found readable newspapers in landfills that were over 40 years old. That is because landfills are not designed to decompose waste, they are designed to store it indefinitely. You simply can’t use landfill results to judge the biodegradation rate of plastics.

The “fish fact” originated in a report titled “The New Plastics Economy — Rethinking the future of plastics”  by the World Economic Forum, the Ellen MacArthur Foundation and McKinsey & Company. Now here is a funny thing, the report doesn’t explain how they generate this claim in its formal text. Instead, they do so in an endnote. A warning: any time a report’s primary statistic comes from a calculation in an endnote you should take that fact with an extremely large dose of salt. Why? because someone clearly decided it was not reliable enough to go in the main text where it would be actively checked by peer-reviewers.

So let’s look at the endnote in question (number 22)

2015-2025 projection of plastics in the ocean based on an estimated stock of 150 million tonnes in 2015 (Ocean Conservancy and McKinsey Center for Business and Environment, Stemming the Tide (2015)), estimated annual leakage rates of plastics into the ocean by Jambeck et al. of 8 million tonnes in 2010 and 9.1 million tonnes in 2015 (J. R. Jambeck et al., Plastic waste inputs from land into the ocean(Science, 2015), taken from the middle scenario), and annual growth in leakage flows of plastics into the ocean of 5% up to 2025 (conservatively taken below the 6.8% annual growth rate in ocean plastics leakage into the ocean between 2015 and 2025 as estimated in Plastic waste inputs from land into the ocean, middle scenario). 2025-2050 projections based on a plastics leakage into the ocean growth rate of 3.5% p.a., in line with long-term GDP growth estimates (International Energy Agency, World Energy Outlook 2015 (2015)).

Admittedly, that sounds pretty convincing, but maybe let’s look into the sources for the numbers. That initial number (starting point of 150 million tonnes) is from the report Stemming the Tide where they write:

An evaluation of the propensity of waste-collection systems to leak plastic waste into the ocean suggests a figure close to 8 million metric tons of leakage per year. In fact, we estimate that the ocean may already contain upward of 150 million metric tons of plastic, based on global plastic production since 1950.

So the critical initial number is a best estimate by another activist group. Readers are provided no supporting documentation nor of any of the assumptions/limitations associated with the number. It simply appears, as if by magic, fully formed for convenient use elsewhere. The problem is that number is inconsistent with most of the other research in the literature which indicates the likely number is almost certainly lower.

The authors then extrapolate the number based on population and growth rates while literally ignoring that the document they are citing (Jambeck et al, 2015 Plastic waste inputs from land into the ocean) notes that measures are being put in place to reduce those numbers. Apparently, all the work being undertaken to reduce the production and release of plastic waste isn’t relevant to this analysis.

Putting it together we have a number that starts from the imagination [sorry did I write imagination? I meant unsupported estimate] of an activist group and is inflated using unrealistic inflationary factors.

Having established that this number is exceedingly unlikely, let’s throw that analysis to the side and imagine that all the assumptions made in the endnote are correct. Imagine their hypothesis is correct and humanity chooses to do nothing to address waste management in the next 30 years. In that scenario, humanity could potentially have dumped 900 million tonnes of plastic waste into the oceans between 1950 and 2050. Given all those assumptions, will all that plastic still be in the oceans in 2050? Of course it will not.

A recent review on the topic (The fate of microplastic in marine sedimentary environments: A review and synthesis, Harris, 2020) gives us some good answers about what happens to plastics in the oceans. As detailed in the review, plastics initially float but eventually most sink where through various physical and chemical mechanisms they are broken down and converted to microplastics. Those microplastics then degrade and are deposited into ocean sediments. As the review notes:

Thus it appears that most microplastic particles are either not reaching offshore to the deep sea environment, or (if they are) they are not remaining in suspension for any length of time, but rather they are exported to the ocean floor; plastic particles that are less dense than seawater eventually sink as a result of biofilm formation (Lobelle and Cunliffe, 2011), expelled as faecal pellets (Cole et al., 2013), or through flocculation and sinking as aggregates (Long et al., 2015; Bergmann et al., 2017; Michels et al., 2018).

What the review article points out is that microplastics behave a lot like other organic materials that enter the oceans. The review also notes that the approximate 8 million tonnes/year of plastics that enter the oceans are dwarfed by the 12.5 billion tonnes/year of sediment delivered by rivers to the coastal marine environment. Understand the oceans are extremely effective at handling marine sediments. Put another way, every year our rivers deposit sediments with a mass equivalent to almost twice the total mass of fish in those oceans and this has raised exactly zero challenge to marine ecosystems.

The truth is that the sediments (and the microplastics) mostly settle out into the sedimentary basins, fjords and estuaries. A recent analysis by Koelmans et al. (2017) estimates that if the input of plastic to the ocean were stopped, most plastic particles would sink to the seafloor within 3 years and eventually become mostly inaccessible from a biological perspective.

To be absolutely clear here, improperly managed plastics are a significant concern that has to be addressed regionally, nationally and internationally. But that is not what our politicians and activists are doing. For those interested Our World in Data has a truly exceptional summary of what we know about plastics and plastic waste and it includes some truly important insights. It notes that 10% of marine plastics are derived from discarded fishing gear. This gear is specially designed to survive in marine environments and represents one of the biggest threats posed by marine plastics.

Ghost Gear (the term for this marine fishing gear) should be a top international priority for coastal countries like Canada. But as the DFO web page on the topic makes clear, our government simply doesn’t take it as seriously as we should. There is lots about meetings and discussions and little about enforceable international agreements. We should be leading an international movement to create enforceable rules about gear abandonment with significant penalties for countries that do not effectively control the abandonment of gear by their fishing fleets. But instead we are spending political capital banning plastics that have no chance of affecting marine ecosystems.

As for regular plastic waste, instead of wasting millions banning straws in Alberta (which will never get to an ocean) we should be spending money helping the Philippines, Vietnam and Indonesia deal with their management of plastic waste while pressuring China (which contributes 28% of mismanaged plastic waste) to do a better job given their desire to be a global leader on so many other topics.

As I have noted more times than I can count at this blog, good environmental decision-making relies on a foundation of good information. The tendency of activists to create and promulgate bad information does little to help their cause. Claiming that the oceans will have more plastic than fish simply does not come off as a serious claim since most of that plastic will be biologically (and physically ) inaccessible nor will it be “in” the ocean but buried below the oceans. Simply put, it is time to have a dialogue based on reliable and reproducible scientific information, not activist-created talking-points. This will allow for the development of effective and politically-supportable policy alternatives.

This entry was posted in Canadian Politics, Chemistry and Toxicology, Uncategorized. Bookmark the permalink.

2 Responses to Debunking the claim that there will be more plastic in the ocean than fish by 2050

  1. Andrew E Boothman says:

    Another great post. Clears up my understanding of how plastic decompose.
    Hope the lack of comments doesn’t discourage future posts.


  2. Neodymigo says:

    Quantity of plastic waste is another number for which one person’s wild guess on the internet becomes the “fact” repeated by science journalists, then finds its way into “expert” reports on behalf of government bodies. Thank goodness for people like you, Blair, who point out that it was nonsense to start with.


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