BY THE TIME CONGRESS ADDRESSES ANY SIGNIFICANT PROBLEM...:

These efforts extend beyond progressive hubs. Cities and mayors that have committed to the 100 percent renewable goal include Atlanta, Evanston, Ill., Fayetteville, Ark., and St. Petersburg, Fla. Among places that have already achieved that goal through wind and solar energy are Georgetown, Texas, Greensburg, Kan., and Rock Port, Mo.

At the state level, Hawaii, New Jersey, New York and Vermont are among those that have committed to using at least 50 percent renewables by 2030. New Jersey's goals are on a par with California's: Through an executive order signed last year by Gov. Phil Murphy, the state will aim to reach 100 percent clean energy by 2050. The state is poised to bolster and revamp its solar-energy and offshore-wind credits systems, and the governor also signed into law a nuclear-subsidy bill that supports the continued use of that energy source.

Though renewable and clean energy are crucial aspects of efforts to reduce global warming, there are other important components to combating the effects of climate change. In response to already increasing extreme weather, a number of cities are proactively addressing development through resilience planning. In the wake of Hurricane Harvey, for example, Houston has been rethinking development: The city is updating rules for building in flood-prone areas and planning new resilience-focused infrastructure, such as a reservoir and coastal storm barrier. Houstoun is a part of the Rockefeller Foundation's 100 Resilient Cities program, created to implement a strategy around climate, social and economic issues.

Minnesota and its cities are also at the forefront, particularly on two crucial areas: transportation and urban planning. The state's Department of Transportation has set a goal of boosting the number of electric vehicles on its roads from the current 6,000 to 200,000 by 2030, and the Twin Cities are building on public transit with new and expanding light rail. Meanwhile, the impressive Minneapolis 2040 Plan promotes substantive rezoning across the city to create denser development. New and existing buildings will be retrofitted or redesigned, and the city will emphasize an array of transportation alternatives including incentives for electric-vehicle charging stations.

(Editor's note: Each story has two sections, the first reflecting the present and the second imagining the world of 2050.)

2019: I went looking for people who've mapped out this world without greenhouse emissions. I found them in Silicon Valley.

Sila Kiliccote is an engineer. The back deck of her house, high up in the hills, overlooks Cupertino. Apple's circular headquarters is hidden in the morning mist. It's a long way from Istanbul, in Turkey, where she grew up; a great place to conjure up future worlds.

"Maybe you'd like some coffee?" Kilicotte says.

Her coffee machine is powered by solar panels on the roof. So is her laptop and her wifi.

"Everything runs on electricity in this house," she says.

This is the foundation of a zero-carbon world: Electricity that comes from clean sources, mainly the sun and the wind, cheap and increasingly abundant.

Today, it powers this house; tomorrow, it could drive the world.

Last year, Kiliccotte quit her job at Stanford University and launched a startup company, eIQ Mobility, helping companies replace their fleets of vehicles, such as delivery vans, with electric-powered versions.

"In order to have impact, timely impact, I figured that I need to leave research and focus on impactful things that I want to do. And fast," she says.

It has to happen really fast. Last year, the world's climate scientists put out a report showing what it will take to limit global warming to 1.5 °C by the end of this century, averting the worst consequences of climate change. It requires bringing the globe's net greenhouse emissions down to zero by 2050.

It's a giant leap for humankind.

So Sila Kiliccotte and I take that leap. Sitting in her kitchen, with solar panels overhead and an electric car parked outside, we pretend that it's happened. It's 2050 and we've stopped climate change.

"Any sense of how we did it?" I ask her.

She pauses. "Yes," she says.

2050: The first step was electric cars. That was actually pretty easy.

"By 2025, battery technology got cheaper," she says. Electric cars were no longer more expensive. "At that point there was a massive shift to electric vehicles, because they were quieter, and cleaner, and [required] less maintenance. No oil change! Yippee! You know?"

Heating and cooling in homes and office buildings have gone electric, too. Gas-burning furnaces have been replaced with electric-powered like heat pumps.

We needed more electricity to power all this right when we were shutting down power plants that burned coal and gas. It took a massive increase in power from solar and wind farms. They now cover million of acres in the U.S., ten times more land than they did in 2020. Huge electrical transmission lines share electricity between North and South America. Europe is connected to vast solar installations in the Sahara desert -- which means that sub-Saharan Africa also has access to cheap power.

"It just changed Africa," Kiliccote says. "It actually fueled the economies of Africa."

We now store electricity so that it's always there when we need it. With batteries, of course, but in lots of other ways, too. For instance, cities are using electricity to heat and chill massive tanks of water, which then heat or cool buildings at any hour of the day or night.

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