The contributions of American cities to global warming

A ranking according to carbon footprint per capita

As centres of energy consumption, the US metropolitan areas should play a leadership role in fighting climate change. That was the starting point for the report 'Shrinking the Carbon Footprint of Metropolitan America' by The Brookings Institution. The report investigates

• the contribution of US cities to carbon emissions
• their potential to reduce this contribution
• the federal policy actions that are needed to achieve such a reduction

The starting point for this investigation is a calculation of the average carbon footprint per capita for the 100 largest U.S. metropolitan areas. This ranking takes road transportation and residential energy use into account. The city with the largest greenhouse gas emissions turned out to be Knoxville, Tennessee, while the least emissions per capita were found in Honolulu, Hawaii.

Room for improvement

As always with this type of study, the results depend a great deal upon the various boundary factors. For example, if air transport had been taken into account, Honolulu would almost certainly lose its top ranking. The boundaries of the metropolitan area are another influencing factor, as it makes a big difference whether the majority of the commuters live inside the area or outside. Various geographical elements such as local climate and whether or not the city is a transport hub can also have an effect.

Apart from those factors — some of which are impossible to change — the carbon footprint of cities is also determined by three main elements that are controllable:

• The energy source for electrical power production; cities in the eastern U.S. tend to have a higher carbon footprint because of the large contribution of coal in the energy mix
• The availability of public transport; southern U.S. cities that rely more on cars than the rest of the country turn out to have higher carbon footprints
• The size and energy intensity of dwellings

The last two elements listed above are the reason why people living in cities generally have a lower carbon footprint than those living in rural areas: they tend to live in smaller dwellings and are less dependent on their cars.

Call for reform

The report concludes by calling for reforms of the existing federal policies, particularly in the areas of public transport and energy use of buildings. One example of such a policy reform is realigning the mortgage interest deduction so that those who purchase the largest and most energy-wasting homes are no longer rewarded. Another proposal is to challenge metropolitan governments to develop innovative carbon reduction solutions that integrate various policy areas.

References

• Report 'Shrinking the Carbon Footprint of Metropolitan America' by The Brookings Institution
• Article 'Which U.S. Cities Contribute Most to Global Warming?' in Scientific American