Why
Planet 10B?

I had dinner with Hans Rosling in 2015, two years before he died. He was already ill, though he did not mention it. What he wanted to talk about was numbers.

Rosling had spent his career as a physician and statistician, fighting what he called "the overdramatic worldview," the tendency of educated people to believe the world was worse than it actually was. He traveled with props: plastic blocks representing population, animated charts that danced across screens, a Swedish accent that turned data into theater.

But that night at dinner, he was not performing. He leaned across the table, fork in hand, and asked me a question. "Do you know what number matters most for the future of this planet?"

I guessed carbon. I guessed temperature. I guessed species.

He shook his head. "Ten billion," he said. "That is how many people will be alive by the time your children are old. Not because of any policy. Not because of any failure. Because the women who will give birth to those people have already been born. The arithmetic is settled." He paused. "Everything else is still a choice."

Ten billion. I had spent years in the environmental movement treating population as a problem to minimize. Rosling was telling me it was a design brief. The actual question was what kind of world those ten billion would inherit.

He died in February 2017, still traveling, still teaching, still fighting statistical illiteracy. His final book, Factfulness, was published posthumously.

I was arrested at the White House in 2013, protesting the Keystone XL pipeline. The D.C. police zip-tied my wrists and walked me to the back of a paddy wagon along with Robert F. Kennedy Jr., Bill McKibben, the actress Daryl Hannah, and a bevy of other activists. We bounced along Pennsylvania Avenue, environmentalists in plastic handcuffs, and I had time to think about what we were actually accomplishing.

The answer, I realized, was: not much. We might delay a pipeline. We might not. We were playing defense on a planet that needed offense, trying to stop construction in an era that desperately needed construction. Different things, built differently, at a scale we had barely begun to imagine.

By then I was the youngest president the Sierra Club had ever had, twenty-three when I took the job, fighting for the California Desert Protection Act, organizing students, building coalitions. Sitting in that wagon I understood we had run out of plan. Stopping things is not a strategy when the world has to build.

What would a plan look like?

The 2024 Living Planet Report confirms what anyone paying attention to wild places already knows. Monitored wildlife populations have declined 73% on average since 1970. The steepest losses are in Latin America and the Caribbean (95%), Africa (76%), and freshwater ecosystems (85%). Around a million species are at risk of extinction, a rate 10 to 100 times the natural baseline.

The causes are well documented. Food production is the leading driver: agriculture uses 70% of freshwater, occupies 50% of habitable land, and accounts for a quarter of greenhouse gas emissions. Since 1970, 35% of wetlands have disappeared. The Amazon is approaching a tipping point: an estimated 14-17% has already been deforested, dangerously close to the threshold beyond which the rainforest may collapse into savanna.

I grew up in Tarzana, California, the town Edgar Rice Burroughs named after his most famous creation. My childhood was spent in the Santa Monica Mountains, in the coastal sage scrub and chaparral that covered the hillsides. I watched those hills get bulldozed for tract housing. I became an environmentalist because I wanted to stop the bulldozers.

Here is what took me decades to see. The bulldozers were not the problem. Sprawl was. Tract housing that replaced wildland could have been an apartment building instead. Low-yield farms expanding into wilderness should have been intensive agriculture on land we already farm. Every coal plant burning for decades is a nuclear plant we did not build.

Protecting those hillsides comes down to permitting apartment buildings. The Amazon survives on higher-yield agriculture, not lower. Coral reefs survive on replacing fossil fuels at a pace we have not yet tried.

In 2010, I visited King Abdullah Economic City in Saudi Arabia with its developer, Fahd Al Rasheed. The project had just been mocked in Dave Eggers’ novel A Hologram for the King, a portrait of Western bemusement at the Gulf states’ ambition to build cities in the desert.

Walking through the construction site, I asked Al Rasheed how he thought about timescale. When would the city be done? "Done?" he said. "Paris is not done. London is not done. We are building a city for three million people who will live here for centuries. We are building the infrastructure first, the ports, the roads, the water systems, and then the city will grow into it." That was the inversion I had been trying to articulate. The whole project assumed the residents had not yet been born.

Rosling’s message was clarity. The ten billion are coming because humanity succeeded: infant mortality dropped, lifespans extended, women started surviving childbirth. Twentieth-century population growth was the demographic echo of people not dying.

Mexico’s fertility rate fell from seven children per woman in 1973 to 1.8 today, below replacement, in a single generation, without coercion. The UN projects population will peak around 2084 at roughly 10.3 billion, then begin a slow decline.

So we are building for a specific number, roughly two billion more than exist today, after which the infrastructure we put in place will serve a population that is gradually shrinking. The design brief has a ceiling. Our ancestors built on similar timescales all the time. The difference is they did it.

In April 2020, in the depths of the pandemic, Marc Andreessen published an essay called "It’s Time to Build." His argument was that America had lost its capacity for construction. We could imagine, we could critique, we just could not get the things we imagined actually built.

I agree with much of what he wrote. But the part I want to add, as someone who has spent a lifetime caring about the environment, is this: building is the only way to protect that environment.

The preservationist instinct is to stop things. Stop the pipeline, the development, the project. On a planet with ten billion people, stopping is not a strategy. We are going to use energy. The choice is whether it comes from fossil fuels or from nuclear and renewables. Two billion more people will need housing. The choice is whether they live in dense cities or in suburbs that eat wildlife habitat.

A zero-emission power plant is a coal plant nobody has to burn. An apartment building near transit is a suburb that does not sprawl. A high-yield farm leaves a forest standing. Desalination keeps a river in its bed. The math works in one direction: built carefully, infrastructure uses less of the planet to support more people on it.

Building for ten billion takes eight interconnected systems, detailed in the Blueprint Plans below: energy, housing, transportation, computing, water, agriculture, materials, and healthcare and education.

Rosling spent his final years teaching people to see the world as it actually was. He showed them the data and the trends. Progress was already happening, he argued, country after country, on one question after another.

And then he told them the hardest part: the ten billion were coming regardless. The only question was what world they would inherit.

That dinner in 2015, when he looked across the table and said "ten billion," he was issuing a design brief, the largest one anyone has ever issued. Our ancestors built aqueducts that still flow, canals that still carry freight, domes that still stand. They built for generations they would never see. For those of us who love wild places, the only way to keep those places intact is to build the rest of the world properly. We have to build.