An Inconvenient Truth About Clean Diesel

The recent Volskwagen emissions scandal is not only about how emissions testing can be avoided by computer programs instead of physical technology that prevents emission. It brings into question the very core of climate policy on light duty vehicles. Around the world we developed emission standards for CO2 emissions, typically in grams of CO2/km, we developed labeling systems, and even emission taxes based on those emissions. Our wishful thinking made us think that the more efficient diesel cycle could be a solution for more climate-friendly cars, as these emitted 20 to 30 percent less CO2/km than gasoline cars. It also made us ignore those spurts of blackish exhaust coming out of these climate cars.

Maybe we thought it was our imagination. What we didn't tell consumers that real-world emissions of Euro 4 diesels were 18 times higher than gasoline. Or that even those brand new Euro 5 or 6 diesels were three to six times dirtier than gasoline. Indeed, mean emissions CO2 from car fleets decreased in European cities. But we were looking past the fact that these cities weren't getting any cleaner in terms of particulate matter and nitrogen oxides -- dangerous components of air pollution, which cause thousands of cases of mortality, cardiovascular disease, and respiratory ailments such as asthma. And now we see how cities have reacted strongly against diesel emissions.

Policy makers face a new challenge now. A year ago policies pointed to promoting "clean diesel." Labelling systems focused only on climate pollutants, and now we face an inconvenient truth. We had been promoting technologies, which may be incompatible with clean air. It's not the first time we've made this mistake. Biofuels were promoted widely a decade ago. Now we see that corn ethanol is far from being carbon neutral if coal fuels its manufacturing processes. We now know that sugarcane ethanol is not so environmentally friendly if we burn the agricultural waste it produces. We have learned that palm oil biodiesel is not friendly to ecological conservation if deforestation is part of its production. And we know that climate and environmentally friendly wood is the always a main culprit of air pollution when it is used for heating.

Our concerns on diesel emissions were addressed in Chile with an integrated green tax, which balances NOx emissions and efficiency in its calculation. The result is that new diesel SUV's must pay a tax between 2000 to 5000 dollars upon purchase. And gasoline cars pay a tax much under 1000 dollars. And when diesel cars are proven to be truly clean they will pay less tax.

This scandal also reminds us that policy makers must be more open to scientific research and the precautionary principal. There are dozens of papers focusing on real-world diesel emissions. Scientists were making testimony on what all cyclists know when waiting in traffic behind a diesel vehicle: that diesel at its current state is far from being deemed clean. And it also reminds us that if we don't integrate our climate and air pollution policies, it will inevitably come at the cost of clean air, human health and livable cities. And we can't afford that cost.