This story originally appeared on The New Republic and is part of the Climate Desk collaboration.

Germany was supposed to be a model for solving global warming. In 2007, the country’s government announced that it would reduce its greenhouse gas emissions by 40 percent by the year 2020. This was the kind of bold, aggressive climate goal scientists said was needed in all developed countries. If Germany could do it, it would prove the target possible.

So far, Germany has reduced its greenhouse gas emissions by 27.7 percent—an astonishing achievement for a developed country with a highly developed manufacturing sector. But with a little more than a year left to go, despite dedicating $580 billion toward a low-carbon energy system, the country “is likely to fall short of its goals for reducing harmful carbon-dioxide emissions,” Bloomberg News reported on Wednesday. And the reason for that may come down not to any elaborate solar industry plans, but something much simpler: cars.

“At the time they set their goals, they were very ambitious,” Patricia Espinosa, the United Nations’ top climate change official, told Bloomberg. “What happened was that the industry—particularly the car industry—didn’t come along.”

Changing the way we power our homes and businesses is certainly important. But as Germany’s shortfall shows, the only way to achieve these necessary, aggressive emissions reductions to combat global warming is to overhaul the gas-powered automobile and the culture that surrounds it. The only question left is how to do it.

In 2010, a NASA study declared that automobiles were officially the largest net contributor of climate change pollution in the world. “Cars, buses, and trucks release pollutants and greenhouse gases that promote warming, while emitting few aerosols that counteract it,” the study read. “In contrast, the industrial and power sectors release many of the same gases—with a larger contribution to [warming]—but they also emit sulfates and other aerosols that cause cooling by reflecting light and altering clouds.”

In other words, the power generation sector may have emitted the most greenhouse gases in total. But it also released so many sulfates and cooling aerosols that the net impact was less than the automobile industry, according to NASA.

Since then, developed countries have cut back on those cooling aerosols for the purpose of countering regular air pollution, which has likely increased the net climate pollution of the power generation industry. But according to the Union of Concerned Scientists, “collectively, cars and trucks account for nearly one-fifth of all U.S. emissions,” while “in total, the US transportation sector—which includes cars, trucks, planes, trains, ships, and freight—produces nearly thirty percent of all US global warming emissions ... .”

In fact, transportation is now the largest source of carbon dioxide emissions in the United States—and it has been for two years, according to an analysis from the Rhodium Group.

There’s a similar pattern happening in Germany. Last year, the country’s greenhouse gas emissions decreased as a whole, “largely thanks to the closure of coal-fired power plants,” according to Reuters. Meanwhile, the transportation industry’s emissions increased by 2.3 percent, “as car ownership expanded and the booming economy meant more heavy vehicles were on the road.” Germany’s transportation sector remains the nation’s second largest source of greenhouse gas emissions, but if these trends continue, it will soon become the first.

Clearly, the power generation industry is changing its ways. So why aren’t carmakers following suit?

To American eyes, Germany may look like a public transit paradise. But the country also has a flourishing car culture that began over a hundred years ago and has only grown since then.