Burning fossil fuels releases carbon dioxide (CO2) into the environment. This is considered to be the primary human contribution to climate change. All countries have contributed to rising atmospheric CO2 levels, but the biggest contributor is China, followed by the United States.
The U.S. experienced a significant decrease in emissions between 2007 and 2013, however, with the amount of CO2 being released falling by 11%. The emissions in 2012, for example, were 5% lower than the levels in 1997. Some people have thanked the shift to less carbon-intensive fuels for this marked decrease. This alteration of fuel-type has shown to be a small factor, but the main contributor to decreased emissions turns out to be a surprising one. It was one of the most devastating economic events this century: the recession. The study that found these results is published in Nature Communications.
Between 1997 and 2007, the U.S. experienced a flourishing economic and population growth. With more people and more cash to splash, the amount of CO2 emissions increased during this 10-year period.
Then, near the end of 2007, the party stopped. This was the time of the economic recession, dubbed the "Great Recession." It's predicted that millions of people lost their jobs, housing price bubbles started to pop up in many parts of the world, and there was a plunge in international trade.
From this point to 2009, there was also a reduction in the CO2 emissions from the U.S. There were claims that this was due to the changes in fuel mix, with an emphasis on less carbon-intensive fuels like natural gas. However, this study finds that this only contributed towards 17% of the CO2 decrease. The primary contributing factor, making up most of the remaining 83% of the reduction, was due to a decline in the consumption of goods. People just didn't have the money to lavish on carbon-emitting products.
Between 2009 and 2013, the economy began to recover from the financial blow. However, this was not married with a rise in CO2 emissions, which is thought to be due to several economic factors. The price of gasoline was high during this period, and a mild winter in 2012 meant lower demand for heat. At this time, companies were also increasing their output of energy-efficient products.
All of these factors are great for reducing the U.S.'s overall emissions. The current decrease is consistent with President Obama's goal of reducing carbon emissions by 17% in 2020 and more than 80% in 2050, relative to 2005 levels. But the real question is: Can this good track record endure as the U.S. economy gets stronger?
The authors suggest that strategies, such as the increase in use of natural gas, will only have a limited benefit in reducing the overall carbon emissions of the U.S. Instead, they look to environmental policies, such as the Environmental Protection Agency Clean Power Plan, to keep emissions in check.
Central Image: Graph of how different energy sources contributed to generating electricity in the U.S. from 1997 to 2013. Nature Communications.