Pollution and Development

Data Highlights

Global mangrove loss

0.1%–0.4% per year (2000–2012)

Hamilton and Casey, 2016

Plastics entering the ocean

4.8–12.7 million MT per year (2010)

Jambeck et al, 2015

Volume of seaborne trade

10.7 billion tons (2017)

UNCTAD, 2018

Cumulative human impacts on the ocean

No area of the ocean is completely untouched by human impact. At a global level, climate change and overfishing represent the greatest threats to the ocean. 1,2,3 Beyond these impacts, the marine environment faces a broad range of human stressors from physical alterations (i.e., coastal habitat loss and changes in freshwater inputs), chemical alterations (i.e., eutrophication, plastic debris, and toxic contaminants) and direct effects on wildlife (i.e., invasive species, vessel strikes, and noise pollution). An attempt to rank ecosystem-level threats from human stressors emphasized the suite of threats associated with climate change, commercial fishing, coastal habitat destruction, and pollution.4

Table 5.1. Top 20 human threats to the marine environment based on ecosystem-level assessments (1 representing the greatest threat)

  1. Increasing sea temperature
  2. Demersal, destructive fishing
  3. Organic, point-source pollution
  4. Hypoxia
  5. Increasing sediment
  6. Coastal development
  7. Direct human disturbance
  8. Organic, non-point source pollution
  9. Coastal engineering
  10. Sea-level rise
  11. Nutrient input
  12. Demersal, non-destructive fishing
  13. Acidification
  14. Species invasion
  15. Nonorganic, point-source pollution
  16. Recreational fishing
  17. Nutrient input, oligotrophic waters
  18. Harmful algal blooms
  19. Nonorganic, nonpoint-source pollution
  20. Aquaculture

This field is largely defined by what do not know; efforts to track the scale and trendline of human stressors face critical data gaps. Although recent advances in technology, including high-resolution satellite imagery, have expanded our understanding of how the ocean is changing, we continue to lack baseline data and long-term monitoring for many aspects of change—including the extent and condition of marine habitats globally. Further compounding these blind spots is the recognition that human stressors interact in synergistic ways, leading to outcomes which are often unpredicted.5

Global hotspots of human impact

A recent study which sought to identify hotspots of human impact identified several areas with consistently high human impacts: the Northeast Atlantic, the eastern Mediterranean, the Caribbean, the continental shelf off northern West Africa, offshore parts of the tropical Atlantic, the Indian Ocean east of Madagascar, parts of East and Southeast Asia, parts of the northwestern Pacific, and many coastal waters.6 Areas with consistently low human impacts were limited to a small number of remote places: the waters off Antarctica, the central Pacific, and in the southern Atlantic.7 This type of data, combined with environmental and socioeconomic factors, can help inform priority areas for research and management.

Fig. 5.1. The most impacted 25 percent of the ocean and the least impacted 25 percent of the ocean

map image

Coastal habitat conversion

Human pressure on the marine environment is most acute along the world’s coastlines. Roughly 40 percent of the global population lives within 100 km of a coastline. This proportion is expected to rise to 50 percent by 2030.8 From draining wetlands and clearing mangrove habitat, to filling in estuaries and hardening shorelines, the conversion of coastal ecosystems has made them one of the most modified and threatened ecosystems globally.

Shoreline hardening reduces the ecosystem services that support coastal populations, including protection from sea-level rise and storm surge. A meta-analysis found that engineered seawalls support 23% lower biodiversity and 45 percent fewer organisms than natural shorelines.9 Global data on overall trends in shoreline hardening are not available, but it is well known that the amount of hardened coastline continues to grow in many ecologically-important coastal regions.10

In major coastal cities such as Hong Kong, Sydney, and New York, more than half of the shoreline is hardened.11 In the United States alone, over 22,000 km (approximately 14 percent) of shoreline have been hardened. In coastal China, the trend of shoreline hardening increased sharply in the early 2000’s, in close correlation with rising GDP per capita in the country.12

Fig. 5.2. Satellite imagery of coastal reclamation in Nahui shore near Shanghai, China

map image

The expanding footprint of human development in the coastal zone has been evident in the loss of mangrove forests worldwide. At least 35 percent of mangrove area was lost globally during the 1980s and 1990s alone; in some regions, the rate of loss was as high as 50-80 percent.13 The rate of global mangrove deforestation has declined significantly in recent years; during 2000–2012, the global deforestation rate was between 0.16 to 0.39 percent per year.14 While the rate of deforestation has stabilized or declined in many countries, Southeast Asia remains the epicenter of mangrove loss, with deforestation rates between 3.6 to 8.1 percent.15 Aquaculture and agriculture have been the principal drivers of mangrove loss in recent decades.

Fig. 5.3. Mangrove area lost by top 20 countries (2000-2012)

Although the global rate of mangrove loss has been declining over the past three decades, several mangrove species remain at high risk of extinction.16 Mangrove forests make up the economic foundation of many tropical coastal regions, providing roughly USD 1.6 billion in ecosystem services worldwide.17 An estimated 80 percent of global fish catches are directly or indirectly dependent on mangroves.18 In recent years, mangrove management has received significant attention as a climate adaptation and mitigation strategy: though mangroves account for only 0.7 percent of the world’s tropical forest area, they contribute 10 percent of total global emissions from tropical deforestation.19

The conversion and degradation of wetlands has also continued at a global level, though there are important regional variations.20 In Europe and North America, the rate of wetland loss has largely declined in recent decades. In contrast, the conversion of coastal and inland natural wetlands has continued at a high rate in Asia.

Tidal flats—defined as sand, rock, or mud flats that experience regular tidal inundation—are one of the most extensive coastal ecosystems, yet their distribution and status has been relatively unknown until recently. A team of researchers used satellite images to map the global distribution and change in tidal flats during 1984–2016. Nearly 50 percent of the global extent of tidal flats is concentrated in just eight countries—Indonesia, China, Australia, the United States, Canada, India, Brazil and Myanmar.21 At least 16 percent of tidal flats were lost globally between 1984–2016.22 Trends suggest continued declines in coverage due to coastal development, reduced sedimentation from major rivers, subsidence of riverine deltas, and increased coastal erosion and sea-level rise.23

Unknown (but growing) toll of population

The aggregate effect of all pollution on the marine environment is not fully known, but indicators suggest that it is likely worsening. Nutrient pollution can have acute impacts—for example, in the form of large-scale nutrient runoff associated with eutrophication (i.e., an excess of nutrients) and subsequent hypoxia (i.e., oxygen deficiency) events. Other pollutants such as bioaccumulating toxins present a more insidious and pervasive threat both to the marine food web and to human health given that they have long half-lives and accumulate at higher trophic levels. Plastic debris, primarily from land-based sources, has received substantial public attention in recent years. Based on current trends, the global quantity of plastic in the ocean could nearly double to 250 million metric tons by 2025—or one ton of plastic for every three tons of fish.24

The most common form of pollution entering the marine environment is the large-scale input of nutrients (i.e., nitrogen, phosphorus), which can result in eutrophication and declining oxygen levels. Deoxygenation is one of the most consequential anthropogenic impacts on the ocean, given that oxygen decline can cause major changes in ocean productivity, biodiversity, and biogeochemical cycles.25 As a proxy for eutrophication, the number of marine “dead zones” or hypoxic sites has continued to increase in number and severity in recent decades. Since 1950, global fertilizer use has increased 10-fold to meet food demands for a growing population.26 As a result of this fertilizer use, nitrogen discharges from rivers to coastal waters increased an estimated 43 percent from 1970 to 2000, with more than three times as much nitrogen contributed from agriculture as from sewage.27 In the United States and Europe, agricultural sources are the primary sources of nutrient pollution in waterways. In South America, Asia, and Africa, urban wastewater is often a leading source of nutrient pollution.

The most reliable maps portraying the global distribution of hypoxic zones primarily point to hotpots in North America and Northern Europe. Presumably, hypoxic areas are more prevalent in many other regions of the world, but a lack of comprehensive monitoring data limits our understanding. Global models are in consensus that the combined effects of climate change and eutrophication will lead to continued decline in oxygen levels in the ocean, likely by a few percent by 2100.28 However, there is uncertainty about the spatial distribution of future hypoxic sites.29 Declining oxygen and the resulting impact on fisheries productivity are likely to affect local economies and food security, particularly small-scale fishers with low adaptive capacity.

Fig. 5.4. Low and declining oxygen levels in the ocean and coastal waters

map image

Plastic debris accounts for the largest portion of marine pollution in the ocean by volume. Roughly half of all plastic ever produced was made in the last 15 years.30 Global plastic production has increased nearly 200-fold, from 2 million tonnes in 1950 to 381 million tonnes in 2015. During 1950–2015, plastic production grew at a compound annual growth rate of 8.4 percent, roughly 2.5 times the rate of global GDP.31 Asia is the leading producer of plastic: nearly 50 percent of global production was in Asia in 2015, of which China accounted for almost 30 percent of production.32

The absolute amount of plastic entering the ocean is difficult to estimate given the wide range of sources and transport pathways. However, plastics are now ubiquitous in the marine environment, found everywhere from the once-pristine Arctic Ocean to remote, uninhabited South Pacific atolls. Recent research indicates that plastic debris is even found in the deepest parts of the ocean, thousands of kilometers from shore, which is concerning given that deep-sea ecosystems have high endemism and very slow growth rates.33 Microplastics are an emerging issue of concern: though there is consensus that microplastics are highly persistent in the environment, there are significant gaps in our understanding of how microplastics affect animal and human health.34

The best available estimates suggest that 4.8 to 12.7 million metric tons of plastic waste enter the marine environment annually from land-based sources.35 The extent and quality of waste management remains a key determinant in terms of which countries contribute the most significant plastic waste inputs per capita from land into the ocean. Over half of plastic entering the ocean comes from five rapidly growing economies—China, Indonesia, the Philippines, Thailand, and Vietnam.36 Interventions in these five countries could reduce global plastic-waste leakage by roughly 45 percent over the next ten years.37 Otherwise, according to current trends, the global quantity of plastic in the ocean in 2025 could be double that of 2015.38

Fig.5.6. Spatial patterns of plastic production and pollution

map image

Entanglement and ingestion of plastic is one of the most commonly documented impacts of plastic pollution on marine life. Notable increases in plastic ingestion have been documented in seabirds and marine turtles alike, with an annual rate of increase of 1.7 percent for seabirds and 0.7 percent for turtles in recent years.39 Researchers expect that both lethal and sublethal impacts from plastic ingestion will result in population-level changes among these marine species.40 While quantitative data remain limited at the global level, an expert survey suggests that among types of plastic pollution, marine mammals are most vulnerable to experience negative impacts from lost or intentionally discarded fishing gear (“ghost gear”), followed by plastic bags.41 Given the increasing accumulation of both fishing gear and plastic bags in the ocean, it is likely that marine mammals have also experienced increasing rates of plastic entanglement and ingestion in recent years.

Fig. 5.7. Increasing effects of plastic pollution on sea bird and sea turtle species

plastic pollution chart

The footprint of ocean industries

The level of industrial activity on the ocean is expected to increase in coming years. According to the OECD, ocean industries generated USD 1.5 trillion in economic activity in 2010; this amount is expected to double to USD 3 trillion in 2030.42 Only a handful of major industries are active on the ocean. Shipping and offshore oil and gas represent the two largest sectors economically and have the most significant ecological footprint on the marine environment outside of fishing. Among sectors with a smaller but still notable footprint, marine aquaculture has grown rapidly over the last two decades. Several other industries—including marine renewables, deep-sea mining, and biotechnology—are on the horizon.

The volume of global maritime traffic continues to grow, with direct and indirect ramifications for the marine environment. The global maritime industry has steadily increased in both the number of ships and in total shipping capacity. Seaborne trade increased by 4 percent to 10.7 billion tons in 2017, the fastest growth in five years.43

Shipping affects the marine environment in several often-diffuse ways. Notably, the shipping sector contributes to climate change (accounting for roughly 3 percent of global carbon dioxide emissions); emits black carbon and other air pollutants associated with heavy fuels; regularly strikes marine mammals; and introduces invasive species through ballast water and fouling. Ocean noise from shipping and other industrial activities is already interfering with communications systems of several marine species and impacts the health of marine life. The level of noise exposure is described as akin to living in a permanent construction zone. According to a recent study, shipping noise could double by 2030.44

Even as seaborne trade of oil has steadily increased in recent decades, available data indicate the number and size of oil spills from tankers have concurrently decreased. In the 1970s, the annual amount of oil entering the marine environment from tankers was approximately 314,000 tons, through almost 80 spills per year.45 By the early 2000s, the average annual amount had decreased to roughly 21,000 tons, and just 6 spills per year.46

Fig. 5.9. Number of oil spills (greater than 7 tonnes)

oil spills chart

Current trends suggest that offshore oil and gas production is slated to increasingly venture into deepwater and ultra-deepwater sectors, as many fields in shallow waters are nearly exhausted.47 As compared to newly discovered onshore fields, recently discovered offshore fields are about 10 times larger, which has provided an economic incentive for industry, in spite of high upfront costs and inherent environmental risk. Global offshore oil and gas production accounted for roughly one-third of total oil and gas output in 2016.48 Over the past decade, offshore oil production has remained steady, while offshore gas production has expanded by nearly 30 percent.49

Fig. 5.10. Global offshore oil and natural gas production by water depth

oil and gas charts

Four countries–Brazil, the United States, Angola, and Norway–account for the majority of global deepwater and ultra-deepwater oil production.50 Since 2005, each of these four countries has increased its share of offshore oil production from deepwater or ultra-deepwater sources; this proportion is highest in Brazil and the United States, which represent about 90 percent of global ultra-deepwater production.51

As the offshore sector increasingly expands into deep and ultra-deep waters of the ocean, studies tracking the implications of the Deepwater Horizon oil spill of 2010 provide insight on the potential risks to ecological and human communities. The Deepwater Horizon spill led to an uncontrolled release of 5 million barrels of oil in the Gulf of Mexico, resulting in immediate death of marine life and substantial financial losses for tourism and fishing industries. However, a recent study found that biodiversity of microbes was flattened at sites closest to the spill, suggesting that the oil may have long-lasting impacts on the ecosystem for years after the initial spill, given that microbes make up the base of the food chain.52

Pollution and Development Notes

  1. Crain, C., B.S. Halpern, M.W. Beck, and C.V. Kappel. “Understanding and Managing Human Threats to the Coastal Marine Environment.” The Year in Ecology and Conservation Biology 1162 (2009): 39-62.
  2. Halpern, Benjamin S., Selkoe, K.A., Micheli, F., Kappel, C. “Evaluating and Ranking the Vulnerability of Global Marine Ecosystems to Anthropogenic Threats.” Conservation Biology 21 (2007): 1301-1315. https://doi.org/10.1111/j.1523-1739.2007.00752.x.
  3. CEA Consulting. “Charting a Course to Sustainable Fisheries.” September 2012. http://chartingacourse.org
  4. Ibid.
  5. Hodgson, Emma and Halpern, B. “Investigating cumulative effects across ecological scales.” Conservation Biology 33 (2018): 22-32. DOI: 10.1111/cobi.13125.
  6. Stock, Andy, Crowder, L.B., Halpern, B.S., Micheli, F. “Uncertainty analysis and robust areas of high and low modeled human impact on the global oceans.” Conservation Biology 32 (2018): 1368-1379. https://doi.org/10.1111/cobi.13141.
  7. Ibid.
  8. Neumann, B., Vafeidis, A.T., Zimmermann, J., Nicholls, R.J. “Future Coastal Population Growth and Exposure to Sea-Level Rise and Coastal Flooding - A Global Assessment.” PLOS ONE 10 (2015). e0131375. https://doi.org/10.1371/journal.pone.0131375.
  9. Gittman, Rachel K, F.J. Fodrie, A. M Popowich, D.A. Keller, J.F. Bruno, C.A. Currin, C.H. Peterson, and M.F. Piehler. “Engineering Away Our Natural Defenses: An Analysis of Shoreline Hardening in the US.” Frontiers in Ecology and the Environment 13, no. 6 (August 2015): 301–7. https://doi.org/10.1890/150065.
  10. Ibid.
  11. Ibid.
  12. Tian, B., W. Wu, Z. Yang, and Y. Zhou. “Drivers, Trends, and Potential Impacts of Long-term Coastal Reclamation in China from 1985 to 2010.” Estuarine, Coastal, and Shelf Science 170 (2016): 83-90.
  13. Romañach, Stephanie S., Donald L. DeAngelis, Hock Lye Koh, Yuhong Li, Su Yean Teh, Raja Sulaiman Raja Barizan, and Lu Zhai. “Conservation and Restoration of Mangroves: Global Status, Perspectives, and Prognosis.” Ocean & Coastal Management 154 (March 2018): 72–82. https://doi.org/10.1016/j.ocecoaman.2018.01.009.
  14. Hamilton, S. and Casey, D. “Creation of a high spatio-temporal resolution global database of continuous mangrove forest cover for the 21st century (CGMFC-21).” Global Ecology and Biogeography 25 (2016): 729–738. DOI: 10.1111/geb.12449.
  15. Ibid.
  16. Polidoro, Beth A., Kent E. Carpenter, Lorna Collins, Norman C. Duke, Aaron M. Ellison, Joanna C. Ellison, Elizabeth J. Farnsworth, et al. “The Loss of Species: Mangrove Extinction Risk and Geographic Areas of Global Concern.”
  17. Ibid.
  18. Ibid.
  19. Murdiyarso, Daniel, Joko Purbopuspito, J. Boone Kauffman, Matthew W. Warren, Sigit D. Sasmito, Daniel C. Donato, Solichin Manuri, Haruni Krisnawati, Sartji Taberima, and Sofyan Kurnianto. “The Potential of Indonesian Mangrove Forests for Global Climate Change Mitigation.” Nature Climate Change 5, no. 12 (2015): 1089–92. https://doi.org/10.1038/nclimate2734.
  20. Davidson, Nick. “How much wetland has the world lost? Long-term and recent trends in global wetland.” Marine and Freshwater Research (2014). http://dx.doi.org/10.1071/MF14173.
  21. Murray N. J., Phinn S. R., DeWitt M., Ferrari R., Johnston R., Lyons M. B., Clinton N., Thau D. and Fuller R. A.. “The global distribution and trajectory of tidal flats.” Nature 565 (2019): 222-225. https://doi.org/10.1038/s41586-018-0805-8.
  22. Ibid.
  23. Ibid.
  24. Worm, Boris, H.K. Lotze, I. Jubinville, C. Wilcox, and J. Jambeck. “Plastic as a Persistent Marine Pollutant.” Annual Review of Environment and Resources 42, no. 1 (2017): 1-26. https://doi.org/10.1146/annurev-environ-102016-060700.
  25. Barboza, Luís Gabriel Antão, A. Dick Vethaak, Beatriz R.B.O. Lavorante, Anne-Katrine Lundebye, and Lúcia Guilhermino. “Marine Microplastic Debris: An Emerging Issue for Food Security, Food Safety and Human Health.” Marine Pollution Bulletin 133 (2018): 336–48. https://doi.org/10.1016/j.marpolbul.2018.05.047.
  26. Breitburg, Denise, L.A. Levin, A. Oschlies, M. Grégoire, F.P. Chavez, D.J. Conley, V. Garçon, et al. “Declining Oxygen in the Global Ocean and Coastal Waters.” Science 359, no. 6371 (2018): https://doi.org/10.1126/science.aam7240.
  27. Ibid.
  28. Ibid.
  29. Ibid.
  30. Geyer, Roland, J.R. Jambeck, and K.L. Law. “Production, Use, and Fate of All Plastics Ever Made.” Science Advances 3, no. 7 (2017). https://doi.org/10.1126/sciadv.1700782.
  31. Ibid.
  32. Worm, Boris, H.K. Lotze, I. Jubinville, C. Wilcox, and J. Jambeck. “Plastic as a Persistent Marine Pollutant.”
  33. Chiba, S. “Human footprint in the abyss: 30 year records of deep-sea plastic debris.” Marine Policy 96 (2018): 204-212. https://doi.org/10.1016/j.marpol.2018.03.022.
  34. Barboza, Luís Gabriel Antão, A. Dick Vethaak, Beatriz R.B.O. Lavorante, Anne-Katrine Lundebye, and Lúcia Guilhermino. “Marine Microplastic Debris: An Emerging Issue for Food Security, Food Safety and Human Health.” Marine Pollution Bulletin 133 (2018): 336–48. https://doi.org/10.1016/j.marpolbul.2018.05.047.
  35. Jambeck, J., R. Geyer, C. Wilcox, T.R. Siegler, et al., “Plastic Waste Inputs from Land into the Ocean,” Science 347 (2015): 768-71.
  36. McKinsey & Company and Ocean Conservancy. “Stemming the Tide: Land-based strategies for a plastic-free ocean.” September 2015. https://oceanconservancy.org/wp-content/uploads/2017/04/full-report-stemming-the.pdf.
  37. Ibid.
  38. Jambeck, J., R. Geyer, C. Wilcox, T.R. Siegler, et al., “Plastic Waste Inputs from Land into the Ocean.”
  39. Worm, Boris, H.K. Lotze, I. Jubinville, C. Wilcox, and J. Jambeck. “Plastic as a Persistent Marine Pollutant.”
  40. Ibid.
  41. Wilcox, C. et al. “Using expert elicitation to estimate the impacts of plastic pollution on marine wildlife.” Marine Policy 65 (2016): 107-114. https://doi.org/10.1016/j.marpol.2015.10.014.
  42. OECD. “The Ocean Economy in 2030.” OECD Publishing, Paris, 2016. http://dx.doi.org/10.1787/9789264251724-en.
  43. UNCTAD. “Review of Maritime Transport 2018.” UNCTAD/RMT/2018. Geneva, Switzerland, 2018.
  44. Kaplan, M. and Solomon, S. “A coming boom in commercial shipping? The potential for rapid growth of noise from commercial ships by 2030.” Marine Policy 73 (2016): 119-121. https://doi.org/10.1016/j.marpol.2016.07.024.
  45. ITOPF. “Oil Tanker Spill Statistics 2018.” 2018. http://www.itopf.org/knowledge-resources/data-statistics/statistics/.
  46. Ibid.
  47. International Energy Agency. “Offshore Energy Outlook” IEA: Paris, France. 2018.
  48. Ibid.
  49. Ibid.
  50. EIA. “Offshore oil production in deepwater and ultra-deepwater is increasing.” EIA, October 28, 2016. Accessed March 18, 2019. https://www.eia.gov/todayinenergy/detail.php?id=28552.
  51. Ibid.
  52. Hamdan, L.J. et al. “The impact of the Deepwater Horizon blowout on historic shipwreck-associated sediment microbiomes in the northern Gulf of Mexico.” Scientific Reports 8 (2018). https://doi.org/10.1038/s41598-018-27350-z.