Rising Seas Threaten Mangrove Forests

Acting as a carbon-sequestering engine, they draw the climate change-causing element from the atmosphere and bury it in the soil. About 8,600 to 6,000 years ago, these forests stored about 85 petagrams of carbon. At that time, it would have been enough to lower carbon levels by 5 parts per million (ppm).

A Balancing Act

Until now, the mangroves have been mostly resilient in the face of sea level rise. They hold their ground as sediment builds up against their roots, which has been observed by recording how quickly sediment accumulates as the land surface elevation near the forests rises.

Because scientists have only a decade or two of data to reference, they wanted to know how well mangroves withstand rising sea levels. They looked at the period in which mangroves first started to appear. After the most recent ice age, between 26,000 and 20,000 years ago, the world started to warm, ice sheets melted, and sea levels began rising at rates faster than 12 millimeters per year. Mangrove forests began to appear as the rise slowed to an average rate of 6.1 millimeters globally.

Scientists used previously published data on 78 organic-rich sediment cores collected from coastal sites around the world, and calculated sea level rise rates for each site using computer simulations. In a high greenhouse gas emissions scenario, sea level rise is projected to increase within the next 30 years to 6 or 7 millimeters per year. Even a mid-range emissions scenario predicts sea rise rates to exceed that threshold by the end of the century. At that point, researchers believe mangroves would not be able to keep up.

Establishing thresholds for mangrove survival is important for future coastal management. Mangroves currently protect 5.3 million people around the world from storm surges. In the future, it may be our turn to protect these life-sustaining ecosystems.