A third of the world's protected areas for wildlife are suffering road-building, more farms and other man-made threats that are undermining goals to safeguard the diversity of life on Earth, scientists warned at a global event.
Almost 200 nations agreed in 2010 to set aside at least 17 percent of the world's land areas in parks and other sanctuaries by 2020 as a cornerstone of a plan to shield animals and plants from pollution, land clearances and climate change.
But many protected areas fall short, according to a report in the journal Science led by researchers at the University of Queensland in Australia.
"Six million sq km (2.3 million square miles) - 32.8 percent - of protected land is under intense human pressure," from threats including more roads, cities, farms and railways, the scientists wrote.
The area is roughly equal to the size of India and Argentina combined. Mangroves, Mediterranean forests, some grasslands and savannahs were among protected areas most at risk.
Overall, governments say the extent of protected lands has roughly doubled since the early 1990s and now covers 15 percent of the world's land in more than 200,000 protected areas, the study said.
Among examples of threats, the study showed satellite images of Kamianets-Podilskyi, a growing city within a national park in Ukraine, roads slicing through Mikumi National Park in Tanzania and farms and other buildings in Dadohaehaesang national park in South Korea.
Among recommendations, countries should improve assessment and management of protected areas, and try where possible to connect them so threatened species can migrate.
A rise of 1.5C degrees Celsius (2.7 Fahrenheit) above pre-industrial times, the toughest goal under the 2015 Paris climate agreement, would mean that only six percent of insects species would suffer a halving or more of their natural habitats.
But risks would rise fast with higher temperatures. Eighteen percent of insects would lose more than half their ranges if temperatures rise 2C (3.6F), the main Paris goal.