A new United Nations proposal calls for national parks, marine sanctuaries and other protected areas to cover nearly one-third or more of the planet by 2030 as part of an effort to stop a sixth mass extinction and slow global warming.

The UN Convention on Biological Diversity released the proposed targets on Monday in a first draft of what is expected to become an update to the global treaty on biodiversity later this year. It aims to halt species extinctions and also limit climate change by protecting critical wildlife habitat and conserving forests, grasslands and other carbon sinks.

Ecologists hailed the plan as a good starting point, while simultaneously urging that more needs to be done.

"We will prevent massive extinction of species and the collapse of our life support system," said Enric Sala, a marine ecologist and National Geographic Society explorer-in-residence, of the draft. "But it's not enough. We need half of the planet in a natural state."

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In an influential study published in April, Sala and others pushed for even more aggressive targets, calling for an additional 20 percent of the world to be set aside as "climate stabilization areas," where trees, grasslands and other vegetation are conserved, preventing further carbon emissions.

Eric Dinerstein, the lead author of last year's study and director of biodiversity and wildlife solutions for the health and environmental advocacy organization RESOLVE , said new climate models and biodiversity analyses conducted in the past year underscored the need to protect more than 30 percent of the planet in the near future.

"If we don't conserve these additional areas between now and 2030 or 2035, we are never going to make a nature-based solution approach work for staying below 1.5" degrees Celsius, the most ambitious aim of the Paris climate agreement.

Conserving more than 30 percent of the planet by 2030 will not be easy. Only 15 percent of all land and 7 percent of oceans is currently protected, according to the United Nations Environment World Conservation Monitoring Centre. These percentages are just shy of the UN Convention's 2020 targets, which call for 17 percent of all land and 10 percent of marine environments to be protected by the end of 2020.

Approximately 190 countries have ratified the Convention on Biological Diversity since it was drafted in 1992. One major exception is the United States, which signed but has not ratified the agreement.

Brian O'Donnell, director of Campaign for Nature, said the 2020 targets are still within reach.

"I think we are very close, and what tends to happen, as we get close to the deadline, that tends to move nations, and often you tend to get some bold announcements," he said.

The 2030 protected area targets, which could increase or decrease in ambition before being finalized, are anticipated to be adopted by governments at a meeting of the UN's Convention on Biological Diversity in Kunming, China, in October.

In addition to reaching spatial targets for protected areas, financing to manage and protect those areas adequately is also key, O'Donnell said.

He added, "that will be the make or break of whether this target is fully effective and works, if wealthier nations, philanthropists, and corporations put some resources behind this to help some of the developing world to achieve these targets as they become increasingly bold."