Mark Pine

In a research report published last month, NASA climatologists collated data on emissions from burning fuels in 16 sectors of the nation’s economy and entered the data into a computer climate model. The result yielded estimates of the effect of each sector on climate warming.

The emissions in the model included CO2, NO, methane, ozone, sulfates, nitrates, black carbon (soot), organic gasses, and aerosols (fine droplets). The economic sectors included road transportation (mostly petroleum-based), household fuel burning (including fossil fuels and biomass like wood), animal farming (a source of methane), electric power generation (coal, petroleum, hydro), industry and manufacturing, and several others.

A few of the results are surprising.

In the near term (now until 2020), road transportation is the largest contributor to emissions that warm the climate by adding heat-trapping gasses to the atmosphere (not very surprising). Unexpectedly, industrial fuel burning is and will remain a net cooler of the climate in the decade to come. Factories emit aerosols, including sulfates, nitrates, and organic molecules that reflect sunlight and prevent warming.

A similarly unanticipated finding is that biomass burning from forest fires and forest clearing for agricultural purposes is cooling the climate at the present time. Forest burning emits a lot of black carbon, which blocks sunlight from reaching the ground.

Power generation emits the largest amount of warming gasses at the present time, and it is a significant contributor to climate warming. But because burning coal and other fuels for power also emits reflective aerosols, the net effect of power generation on climate heating isn’t as great as road transportation.

Cooling due to factory emissions, forest burning, and power generation, however, provides only cold comfort. These emissions degrade air quality and cause serious and severe health problems. They must be cut to protect health and reduce forest loss. In the coming century, the cooling effects of these sources of emissions will be eliminated and their net warming effects will increase. By 2100, power generation will become the largest contributor to global warming, followed by road transportation and industrial fuel burning.

In the near term, the NASA research shows that the largest contribution to reducing emissions would come from downsizing the road transportation sector. Doing so would cut warming emissions without significantly affecting cooling aerosols. Nadine Unger, the lead NASA scientist on the research, put it this way:

“Targeting on-road transportation is a win-win-win,” she said. “It’s good for the climate in the short term and long term, and it’s good for our health.”

Increasing use of rail transportation to replace car commuting and truck freight would seem like the way to go.

In this connection, a new PBS series, Blueprint America: Beyond the Motor City aired last month. It’s a remarkable documentary showing how Amercans’ wholesale adoption of the automobile for transportation destroyed urban life in the 20th century—an epoch that might justifiably be called the Automobile Century.

It explains how our love affair with the car, the massive construction of roads, and the resulting flight of families to the suburbs destroyed the economic basis of cities. It also impoverished the remaining city residents, causing urban blight, segregation in ghettos, and racial riots. And it’s still going on.

Now the new NASA report makes it clearer that ubiquitous use of the automobile for personal transportation and use of trucks for freight—which was promoted by federal policies supporting highways and freeways and neglecting rail—has also probably been the main driver of global warming for the last hundred years.