Rising sea levels threaten key coastal areas like the Mekong Delta, which produces the majority of Vietnam's rice. The only thing standing between the country and the ocean is a tree.

It was overcast, and Hoi An's colours softened like a watercolour painting. I paused for the requisite photo of the red Japanese Bridge, the city's landmark. It hung elegantly between grey clouds and the shimmering canal, a memory from the 1700s when this Vietnamese city was an international trading port. Yet as I raised my camera, I wasn't imagining the picturesque past, but rather a questionable future.

Vietnam is in danger. Rising sea levels pose a huge threat to this coastal country. In less than 100 years much of southern Vietnam's Mekong Delta - the heart of the nation's rice production - could go the way of Atlantis. The Ministry of Natural Resources and Environment predicts that the ocean will swallow more than a third of the region by the year 2100, taking a swath of Ho Chi Minh City with it. Halfway up the coast from the Mekong Delta, Hoi An's prognosis is better, but it's not immune. The city sits where the Thu Bon River meets the South China Sea. Its inhabitants are already used to hauling furniture upstairs during seasonal floods.With a dire forecast and limited resources, Vietnam doesn't have a lot of options. In 2015, then Minister of the Environment Nguyen Minh Quang told the press that the country's best bet was to plant more mangrove trees.

Mangroves are the climate superheroes of the arboreal world. They grow in swamps along the coasts: thin trunks and tangled, spidery roots submerged in dark, briny water. The roots filter saltwater and can expand eroded coastlines. They also create natural storm barriers and protect agricultural land from saltwater infiltration. And on top of everything else, mangroves are atmospheric vacuum cleaners, pulling unparalleled amounts of carbon dioxide from the air.The organic carbon stocks stored in mangrove ecosystems are three to five times larger than other forest types," confirmed Sigit Sasmito, a researcher with the Center for International Forestry Research and Charles Darwin University in Australia.

However, Vietnam has lost more than half its mangrove forests since the 1940s, largely to aquafarming and urban development. It's the eternal conundrum of environmentalism in developing economies: eat now or breathe later? Clearing land for shrimp farms might be beneficial in the short term. But intact forests are hugely profitable to the fishing industry at large: by keeping salinity levels in check, mangrove forests promote tremendous biodiversity, which means more kinds of fish to catch.