Although coastal and freshwater wetlands – such as swamps, mangroves and marshes – contain 40 percent of all plant and animal species, many are polluted or degraded due to climate change and human development.
On World Wetlands Day Thursday, the UN called for urgent action to revive and restore these ecosystems, which are disappearing three times faster than forests.
Wetlands cover roughly six percent of the Earth's land surface and are vital for human health, food supply, tourism and jobs.
More than a billion people worldwide depend on them for their livelihoods, while their shallow waters and abundant plant life support everything from insects to ducks to moose.
Wetlands also play a crucial role in both achieving sustainable development and the fight against climate change.
They provide essential ecosystem services such as water regulation, and reducing the impact of flooding, for example.
Peatlands, a particular type of vegetated wetland, store twice as much carbon as forests.
However, over the past 200 years, wetlands have been drained to make way for farmland or infrastructure development, according to the UN Environment Programme (UNEP).
Roughly 35 percent of all wetlands globally disappeared between 1970 and 2015, and the rate of loss has been accelerating since the year 2000.
Depending on the amount of climate-related sea level rise, some 20 to 90 percent of current coastal wetlands could be gone by the end of the century, the UNEP said.
Wetlands have also suffered more biodiversity loss than other land and marine ecosystems.
Leticia Carvalho, head of the agency's Marine and Freshwater Branch, urged governments to end policies and subsidies that incentivise deforestation and wetlands degradation, and urgently focus on restoration.
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"At the same time, we must guide and drive investments to protect priority ecosystems, such as peatlands, and encourage the private sector to commit to deforestation and peatland-drainage-free supply chains," she added.
Recently, governments have been stepping up efforts to protect wetlands.
At the UN Biodiversity Conference in December, countries agreed a landmark deal to protect a third of the planet's lands, coastal areas and inland waters by 2030.
Action to restore wetlands is gathering momentum around the world. For example, China is developing the "sponge cities" concept, in the face of rapid urbanisation and intensified climate hazards, including flooding.
Initiatives include "green" rooves, constructed wetlands and pavements that capture, slow down and filter stormwater.