Possibly the worst impact of all those additional vehicles will be the new roads they spawn. It’s currently projected that, by 2050, the world will have another 25 million kilometers of paved roads—enough to encircle the planet more than 600 times.

Today, new roads are being constructed virtually everywhere, including many of the world’s last surviving wild places. We build roads to log forests, to extract fossil fuels and minerals, to increase economic growth and trade, to defend our borders, and to integrate our economies. Around 90% of new roads will be constructed in developing nations, home to the majority of the world’s tropical and subtropical forests—the most biologically rich real estate on the planet.

It would be one thing if we’d just build the roads, but they also open up wild areas to a Pandora’s box of environmental ills—ranging from increased wildlife poaching and forest destruction to wildfires, illegal mining, and land speculation. For example, my research team showed that in the Brazilian Amazon, there are nearly three kilometers of illegal roads for every one kilometer of legal road. Once you map all those roads, you find that 95% of all deforestation in the Brazilian Amazon occurs within 5.5 kilometers of a legal or illegal road.

In many parts of the world, roads are opening up the last surviving stretches of wilderness like a flayed fish. In the Congo Basin, the construction of more than 50,000 kilometers of logging roads has allowed poachers, armed with rifles and cable snares, to conduct a systematic slaughter of wildlife. In the last decade, two-thirds of all forest elephants have been killed. In sub-Saharan Africa, our analyses suggest that a scheme to construct 33 major “development corridors”—spanning some 53,000 kilometers in total—could imperil more than 2,000 parks and protected areas, either by bisecting them or by promoting increased development and poaching around the park.

Globally, the frenetic expansion of roads is probably the single greatest threat to nature. Climate change is eroding ecosystems like an acid, but the proliferation of roads, and the massive environmental perils they bring, are battering away at them like a sledgehammer.