Between 15 and 51 trillion pieces of plastic are now afloat on the World’s oceans. This is a key finding of the scientific team that published the most recent major study (December 2015) focussed on refining the global estimates of plastics floating on the oceans. The new estimate is three to ten times larger than an earlier one in 2014 which reported around 5.25 trillion items were afloat globally. The most recent study also estimates the weight of these floating plastics at between 93 and 236 thousand metric tons, which is only approximately 1% of the total global plastic waste estimated to have entered the World’s oceans in 2010.
The new study published in December 2015 was coauthored by three of the authors of the previous work, along with other scientists, and pulls together all previous survey results, related assessments and additional survey data to come up with the new estimates. Both the 2014 and the 2015 studies are based in part on the results of extensive surveys from 24 expeditions across the five major rotating ocean current regions (known as ocean gyres) of the sub tropics as well as coastal Australia, the Bay of Bengal and the Mediterranean Sea. The authors of the 2015 study state ‘we use the largest dataset of microplastic measurements assembled to date to assess the confidence we can have in global estimates of microplastic abundance and mass”. The authors also state “these estimates are larger than previous global estimates, but vary widely because the scarcity of data in most of the world ocean, differences in model formulations, and fundamental knowledge gaps in the sources, transformations and fates of microplastics in the ocean.” The authors of the earlier 2014 study stated in their report “our estimates are highly conservative”.
A global inventory of small floating plastic debris
van Sebille et al. Environmental Research Letters Volume 10, Number 12. 8 December 2015