Ocean Warming Projected to Stall Expected Mangrove Recovery

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Increasing ocean temperatures will erase mangrove restoration gains expected to occur due to economic development and conservation, according to a new study from researchers at UC San Diego's Scripps Institution of Oceanography.

The study, published in Environmental Research: Climate, projects that by 2100 the world would lose out on some 150,000 hectares (370,000 acres) of mangroves and associated ecosystem services worth $28 billion annually, with Asia bearing nearly two-thirds of these losses. The findings bolster the economic case for reducing greenhouse gas emissions and suggest that conservation targets for mangroves may need to become even more aggressive to outpace climate change, said the authors.

Mangroves are salt-tolerant trees with intricate, exposed roots that grow in intertidal zones in tropical and subtropical regions. The coastal wetlands they form protect coastal human communities from storm surges and tsunamis, create habitat for fish and other wildlife, store carbon and improve water quality.

After decades of heavy losses, mangrove forest destruction has slowed due to increased recognition of their importance as well as economic development.

"As a country gets richer you tend to see an initial increase in environmental destruction, but once a place achieves a certain level of economic development the environment degradation starts to diminish," said Katharine Ricke, a climate scientist at Scripps and co-author of the study.

Climate change, however, is warming the world's oceans, and in some parts of the world, these increasing temperatures can exceed the limits of what mangroves can tolerate.

With these two opposing forces in mind, the study authors wanted to use satellite imagery and statistical analysis to peer into the future of these important coastal ecosystems.

Beginning in 2022, the team analyzed high-resolution satellite data on mangrove forest coverage from 1996 to 2020, and combined them with local economic indicators and ocean surface temperature records for 1,533 locations worldwide. Using panel data analysis - a statistical technique that examines changes over both time and space - the researchers isolated the effects of changes in sea-surface temperature and gross domestic product in these places from other factors like local governance and conservation policies. The researchers then projected future mangrove coverage under various climate and economic scenarios through 2100.

The analysis found that while economic growth and the associated increases in conservation would restore substantial mangrove coverage over time, warming oceans almost entirely cancel out these gains.

"Socioeconomic and policy forces are currently strong enough to cancel out climate damage to mangroves, resulting in stability rather than decline," said Ricke. "But our projections show we need to accelerate both conservation efforts and emissions reductions to keep making progress for mangroves."

Neither factor - economic development and ocean warming - had a strictly linear relationship with mangrove forest recovery. Warming initially helped mangroves in cooler regions, before becoming destructive beyond a threshold, and economic development first caused mangrove destruction before nations became wealthy enough to invest in protections.

In high-emissions climate scenarios, mangrove forests could shrink by some 150,000 hectares by 2100. The economic value of the lost ecosystem services by 2100 totals roughly $28 billion per year.

"We need to keep pushing to protect these ecosystems because they can both help us fight climate change and adapt to its impacts," said Ricke.

The lost ecosystem services in 2100 predicted by the study were unequally distributed: Asia faced $18.6 billion in annual losses, the Middle East and Africa $5.4 billion, Latin America and the Caribbean $3.6 billion, while wealthy nations lost less than $1 billion.

"We keep finding that while climate change damages ecosystems broadly, the impacts on people's well-being are far from evenly distributed," said Bernie Bastien-Olvera, who led the study during a postdoctoral fellowship at Scripps and is now at the National Autonomous University of Mexico. "These unequal losses deepen existing inequalities, and they are often absent from conventional climate impact metrics. "

The researchers suggest that these findings need to be factored into attempts to calculate the economic damages caused by continued greenhouse gas emissions, such as the social cost of carbon. Ricke said such calculations have historically failed to adequately incorporate the value of ocean ecosystems. The team also calls for those working in mangrove conservation and restoration to integrate climate projections into their targets, because achieving mangrove recovery is likely to require more aggressive action than expected.

In addition to Ricke and Bastien-Olvera, the study was co-authored by Octavio Aburto-Oropeza and Fabio Favoretto of Scipps Oceanography as well as Elmer Urbano of UC San Diego, Scripps alumnus Dillon Amaya, now of NOAA and Luke Brander of Leibniz University Hannover.

Learn more about research and education at UC San Diego in: Climate Change