The environmental footprint of humanity is truly massive. Indeed, over our planet’s entire 4.5 billion-year history—at least two-thirds of which has sustained life—no other species has ever come close to us in terms of consuming so much of the world’s energy, resources and land area. But despite the growing human footprint, there are still wild places where natural ecological and evolutionary processes operate with minimal disturbance from urbanization, energy and transportation infrastructure, agriculture, mining and logging. Though those last untouched spaces are shrinking at a harrowing rate.

In research published in September, my colleagues and I showed that just 20 percent of Earth’s land surface now survives as wilderness. The majority is located in cold or dry places in North America, North Asia, North Africa and the Australian continent. Comparisons between recent maps of wilderness areas and those in 1993 show that an estimated 1.3 million square miles—almost 10 percent—was lost in the intervening years. This is equivalent in area to half of the continent of Australia or twice the size of Alaska. Hardest hit were South America, which has experienced a 30-percent wilderness loss, and Africa, which has experienced a 14-percent loss—in just over two decades. The Earth’s last intact wilderness areas are dramatically shrinking.

In a time of increasingly rapid environmental change, these areas are the final strongholds for endangered biodiversity. They are also essential for sustaining the complex processes that underlay important regional- and planetary-scale climate functions. It is now becoming realized that large, intact systems store more terrestrial carbon than disturbed and degraded ones and are far more resilient to disturbances such as rapid climate change and fire. For instance, the Boreal Forest remains the largest biome undisturbed by humans, and stores roughly a third of the world’s terrestrial carbon. Yet this globally significant wilderness area is increasingly threatened by industrial logging, oil and gas exploration, human-lit fires and climate change, which collectively threaten a biome-wide depletion of its carbon stocks—considerably worsening global warming.

In this Anthropocene era, where the human footprint is now altering many of Earth systems processes, wilderness areas serve as natural observatories where we can study the ecological and evolutionary impacts of global change. They also serve as natural controls for comparison with areas where intensifying land use and land cover changes are occurring. As intact, large-scale ecosystems become rarer, their value is increasingly appreciated. For instance, we are already seeing growing efforts to ‘‘re-wild’’ some human-dominated ecosystems in Europe and North America; remaining wilderness areas provide the reference points and biological feedstock for these initiatives. Without concerted preservation of existing wilderness areas, there will be a diminished capacity for large-scale ecological restoration.

We need immediate, proactive action to protect the world’s remaining wilderness areas. This means nations need to identify those remaining areas that are at greatest risk and setting clear targets for their immediate conservation. There are important opportunities for nations like Canada, the USA, Australia and Brazil to show global leadership on this, as they still have large areas of globally significant wilderness. At a broader societal level, we need to become more efficient in our exploitation of the planet, at least in terms of our overall land-use footprint. The alarming loss of these lands is a tragedy both for nature and humanity. Protecting the world’s last wild places is not just a cost-effective investment. It is the only way to ensure that some semblance of intact nature survives for the benefit of future generations.

Watson is an associate professor at University of Queensland and director of the Science and Research Initiative at the Wildlife Conservation Society.

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