The Best Way to Slow Global Warming? You Decide in This Climate Simulator

It was on Earth Day 2016 when more than 170 nations signed the Paris Agreement calling for limiting global warming “to well below 2°C.” Putting together the terms took years, with the difficult diplomatic work wrapped up by the end of 2015. Of course, the world’s climate emissaries would want to wait for a more dramatic date to sign.

We’re now five Earth Days since Paris, and 50 years since the very first Earth Day. The world has moved from an average temperature increase of 0.06°C in April 1970 to 1.16°C today. That means we’re nearly 60% of the way towards breaching the Paris target, and a stretch goal of staying below 1.5°C is all but dead.

But these decades have not been entirely wasted. Many of the necessary fixes that could only be imagined 50 years ago are now in hand, so no one needs to wait any longer for the futuristic climate solutions to be invented.

In fact, we’ve already seen most of the large-scale solutions successfully deployed somewhere in the world. Electric vehicles make up more than half of Norway’s passenger vehicle sales. The U.S. has retired 20% of its coal-fired power generation since 2012. Indonesia reduced its rate of tree-cover loss by 60% in 2017.

That means we now have enough data to measure the relative effectiveness of major climate solutions. Whether you’re a head of state, corporate executive, climate activist or bystander, there haven’t been easy ways to test your preferences. Would taxing fossil fuels be more powerful than a carbon tax set at $100 per metric ton? What happens to renewable energy if nuclear fusion becomes viable by 2030?

Climate Interactive, a nonprofit think tank, has spent the last nine years developing a tool with the MIT Sloan Sustainability Initiative and Ventana Systems Inc., dubbed En-ROADS, that lets everyone test the impact of climate solutions. It’s a policy simulator designed for use in role-playing workshops for negotiators, academic seminars, and as a learning aid for curious individuals.

Read More: The Professor Who Turns Climate Change Into a Game

Bloomberg Green has used En-ROADS as an engine to create a simplified scenario menu, streamlining the mechanics just enough to let regular people test their assumptions about specific climate solutions — and what it will take to keep the world below 2°C.

No Silver Bullets

These are our starting points for the trajectories of greenhouse-gas emissions and global temperatures, and this is our underlying rule: There are no panaceas among climate solutions. The most well-known fixes are not necessarily the most effective at stopping the planet-warming pollution. That doesn’t mean marginally effective solutions aren’t useful or important, nor does it mean an incomplete fix shouldn’t be pursued. But in some cases the all-or-nothing terms of the debate may not match the potential effect on the real world.

Electric Vehicles

Drivers bought 2.1 million electric cars in 2019, almost half of them in China. That number is projected to rise to 46 million by 2039, the first year when battery-powered cars are expected to outsell internal-combustion engines, according to research from BloombergNEF. What if a combination of consumer rebates and investment in electric cars, trucks, buses and trains by companies and governments could speed up the transition away from combustion engines?

There are limits to the electric revolution, at whatever speed it plays out. Even in a scenario like this one, in which two-thirds of all transportation eventually goes electric, oil retains its hold on worldwide transportation until the 2040s. It takes that long for nations to finally build out their charging infrastructure and for existing combustion engines to retire. Hundreds of millions of EVs will also need a lot more electricity generation, and, without limits on fossil-fuel investments, most of it would come from coal and natural gas.

If renewable power grows to keep up with this demand, the transformation will be more powerful. Electric cars are only as clean as the power generation that feeds them.

Nuclear Power

Everyone knows the best thing about nuclear power generation: zero CO₂! But we’re also familiar with the tremendous expense and time involved in bringing new nuclear plants online, not to mention the difficulties in safeguarding radioactive waste and preventing terrifying mishaps. In this simulation, however, we can clear those hurdles and look at a best-case scenario for new nuclear capacity.

A high nuclear subsidy shaves off about 8% of CO₂ emissions from baseline projections, leaving the world 0.2°C cooler in 2100 than otherwise. Adding nuclear plants reduces the amount of coal- and gas-fired power generation across the planet—but also has a similar negative impact on the growth of renewables. In the En-ROADS model, it takes a couple decades for the nuclear industry to grow to scale and cheaper power competes with fossil fuels. During that time, coal, oil and gas burning would continue apace, exactly when we need emissions to taper off.

Renewable Power

From the perspective of cutting emissions, the best global energy mix is 100% renewable power. But En-ROADS is a real-world policy tool, so its settings mimic things that real-world governments can actually do. In this case, it’s subsidizing clean power generation to speed up the energy transition.

Enlarged renewable subsidies have surprisingly limited effect on overall global temperature. Solar and wind power ramp up over the course of the century, cutting warming by a small margin and decreasing the amount of CO₂ by less than the nuclear build-out scenario above. Without deploying complementary policy tools that discourage fossil-fuel use, the second-, third- and fourth-biggest energy sources in 2100 will remain coal, oil and gas.

Direct Air Capture

There are several viable technologies that promise to draw down some of our climate pollution. Direct air capture has attracted much attention and investment, for its ability to remove CO₂ directly from the atmosphere. While the science behind it is increasingly solid, scaling up hasn’t yet been possible because costs are high and storing the CO₂ underground forever is a steep challenge. Let’s see what happens under a best-case scenario for direct air capture.

Without complementary policies, direct air capture leaves the fuel mix the same—and that means the energy required to run it will often come from sources that create new emissions. Compared with some academic estimates, En-ROADS is conservative in its assumptions for how much carbon-dioxide removal will be possible anytime soon.

Replanting Forests

Planting trees is the least people can do, having felled half the world’s tropical forests in just the last half-century. Trees remain the most successful CO₂-scrubbers in the history of the planet, there’s no debate about that. Scientists argue over how much of the planet can be dedicated to re-seeding forests. Let’s try a scenario that goes big on afforestation.

It takes decades for photosynthesis to store CO₂ in vegetation and soils. Not only does mass afforestation barely change the projections, it creates possible competition with other important uses of land, including growing food and energy crops. This result is close to the opposite of the halo that surrounds most pro-tree policies.

Carbon Tax

The most powerful button in this simulator is also the most politically fraught: a carbon price. Economists have long had a seductively easy answer to how to get governments, companies and consumers to change their behavior. Humans respond to prices, and carbon pollution in most places remains un-priced. With help from En-ROADS, we can see the impact of something that has never been attempted: a global tax on carbon emissions.

Look at that—a policy that dramatically changes our projections. En-ROADS is hardly alone in emphasizing the power of a carbon tax. The International Monetary Fund recently recommended a global carbon price of $75 a ton to help put the 2°C goal within reach. There is an existing patchwork of carbon taxes, covering the European Union, the U.S. Northeast, California, South Africa and dozens of other nations and regions. Those in Sweden, Switzerland and Liechtenstein exceed $75 per ton. And that price might not prove high enough. The longer the world waits to implement a carbon price, the higher that price needs to be to keep the 2°C goal alive.

Play the Game

Promoting a single policy, energy source or climate solution is always too narrow. Calls for “all of the above” are too vague to be practical. In the space between lie many potential approaches.

Below is a way to test some of them. Click all the boxes at once, or pick and choose to see how close different combinations bring you to the 2°C goal. Using the full En-ROADS tool itself, you can dig deeper and fine-tune different policies and assumptions to design your own pathway.

These buttons have been calibrated to bring the solutions on offer as close as possible to practical or middle-of-the-road scenarios. Remember: To hit 2°C, these solutions have to happen everywhere, not just somewhere.