The world needs a new international protected area target based on scientific evidence, according to a team including University of Queensland scientists.
UQ researcher Professor James Watson, who is also with the Wildlife Conservation Society, said protected areas were critically important for safeguarding biodiversity.
"We know protected areas work. When well-funded, well-managed and well-placed, they are extremely effective in halting the threats that cause biodiversity loss and ensure species return from the brink of extinction," he said.
Dr Piero Visconti, lead author of the manuscript, from the International Institute for Applied Synthesis Analysis, said the current international target, accepted by more than 190 nations, was failing to protect species.
"While there has been a significant increase in the overall coverage of global protected areas over the past 10 years, many new areas are in sites that are not as important for biodiversity," he said.
"At the same time, other more important sites are left unprotected and are vanishing before our eyes.
"There's also clear evidence that the vast majority of protected areas are not being funded and managed in ways to stop damaging human activities."
The study identified four broad problems with the protected area target - Aichi Target 11 - established in 2010 as part of the Convention on Biological Diversity.
The target requires at least 17 per cent of terrestrial and inland water areas and 10 per cent of coastal and marine areas be protected by 2020.
The researchers argue that this policy has led to perverse outcomes, with signatories unable to account for real progress.
"What we need is effective outcome-based targets for protected areas to help us achieve biodiversity goals and help determine conservation sites beyond 2020," Dr Visconti said.
"It's time to put emphasis on measuring and achieving the end-goal of conservation, reaching and maintaining long-term positive biodiversity status and trends.
"We need targets that are qualitative, not just quantitative."
Professor Watson said many protected areas that were still in good condition were the last strongholds for endangered species worldwide.
"The immediate challenge is to improve the management of those protected areas that are most valuable for nature conservation, to ensure they safeguard it," Professor Watson said.
"Beyond this, we need all nations to be honest when accounting for how much land they have set aside for biodiversity conservation and, as we approach 2020, the global conservation community needs to stand up and hold governments to account.
"Governments need to take the conservation of their biodiversity seriously, and this means setting a protected area target that will achieve the right outcome."
The study is published in Science (DOI: 10.1126/science.aav6886).