Mangroves on Cayo Coco in Cuba. Photo: Prisma by Dukas/UIG via Getty Images

Human activities are encroaching on the lands we've set aside to protect vulnerable species, according to new research.

Key findings: The study, published Thursday in Science, found that about 33% — or roughly 2.3 million square miles — of protected land worldwide is under "intense human pressure" from development, such as roads, growing urban areas, and agriculture. Only 42% of protected land is free of any "measurable human pressure," the researchers found.

What they did: The study's authors devised a metric for the human footprint on our planet that includes proximity to built environments, pasture lands, intensive agriculture, nighttime lights, and human population density, among other variables. Protected lands include national parks as well as World Heritage sites and other types of areas designated as off-limits to development.

  • On a positive note, the average human footprint within protected areas was almost 50% lower than the global mean for all types of land areas.
  • But just 4,334 protected areas, amounting to 10% of analyzed protected areas, "are completely free of intense human pressure," they wrote.
  • Such areas tend to occur in remote parts of the globe, such as parts of Russia and Canada, rather than the tropics, which are both rich in biodiversity and have human populations encroaching upon them.

Most at risk: Of the types of biomes that are facing a particularly high amount of human pressure, mangrove forests lead the list. These aquatic forests serve as fish nurseries and protect shorelines from storm surge flooding.

  • Others shown to be under high pressure despite their protected status include tropical coniferous forests and flooded grasslands and savannas.

Be smart: Interestingly, the combined metric used in the study — known as the human footprint score — could lead conservationists in the wrong direction, warns Rob McDonald a conservationist at the Nature Conservancy, who was not involved in the new study.

He says conservationists have successfully carved out well-functioning land reserves near or even within urban areas, but that under this study, these would receive a high human footprint score. Such a score could discourage policymakers and groups from pursuing additional protected areas near urban settings.

“I just view doing land protection near human activity as part of doing conservation in the 21st century," McDonald says.

In related news: The findings relate to another study published in Science on Thursday that looked at a staggering number of species — 115,000 — to see how limiting global warming to different levels would vary in their impacts on species.

  • The researchers counted the number of species projected to lose more than half their geographic range due to climate change, which could make areas unsuitable for many species.
  • They found that on the current global warming trajectory, with global average temperatures increasing by at least 3 degrees Celsius, or 5.4 degrees Fahrenheit, compared to preindustrial levels, nearly 50% of insects would lose half their range.
  • This would fall to just 6% of insect species if warming were held to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels — the goal of the Paris Agreement.

Previous studies looking at how global warming would affect species' ranges had not focused on insects, despite their value to keeping ecosystems healthy, such as through pollination.

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