Mobility clearly is essential to economic growth, but in our carbon-based world moving people from place to place exacts a steep price.

Consider just the United States. In 2017, the transportation sector accounted for 29% of the nation’s total emissions of 6.4 billion metric tons of carbon dioxide equivalent, or CO2e (the CO2 equivalent of an individual greenhouse gas).

Driven largely by the transportation sector’s emissions of fossil fuels, concentrations of CO2 have risen steadily since the early 1980s, except for the period beginning with the start of the last recession in late 2007, according the U.S. Energy Information Administration.

Annual CO2 emissions from transportation had reached more than two billion metric tons in 2007 – the highest level since the EIA began keeping records in 1973. By 2012, about four years into the recession, emissions had fallen to about 1.8 billion metric tons. But with the economic recovery, emissions began to rise again. By 2018, transportation emissions totaled 1.9 billion metric tons for the year – just under the 2012 peak.

Despite the rise of electric car manufacturers, new public transit projects in cities across the nation, more fuel efficient aircraft engines, and other innovations in mobility, it’s clear that economics is the main driver of carbon emissions from transportation. When the economy is growing they go up; when it’s contracting they go down.

Globally, the picture is similar, and in its most recent report on climate change, the Intergovernmental Panel on Climate Change in 2014 offered a stark forecast: By 2050, global emissions of greenhouse gases from transportation could grow to about 12 billion tons of CO2e annually – unless there are aggressive and sustained changes in how humans get around. Globally, the transportation sector in 2010 – as reported then by IPCC – was responsible for about 23 percent of total energy-related CO2 emissions worldwide.

Transportation and the carbon emissions it creates make for a big and unwieldy topic. But reviewing a few key areas can help improve understanding of some of the challenges ahead.

The impact of driving

Many Americans love to drive and love their cars – or at least the notion of car ownership. In 2018, there were 281.3 million vehicles registered in the U.S., according to Hedges & Company, an automotive marketing and research agency based in Hudson, Ohio. Americans collectively drove more than three trillion miles in 2017, the most of any year since record keeping began in 1980, according to the Federal Highway Administration. Emissions from light-duty vehicles in the U.S., such as cars and pickup trucks, came to nearly 1.1 billion metric tons of CO2e – about 17% of all carbon emissions in the country.

How can we collectively reconcile a need to reduce carbon pollution with peoples’ widespread fondness for driving, often with just a driver, no passengers, even in congested urban areas? The New York Times in August ran a short but provocative piece that suggested people can make big changes in carbon emissions with fairly little effort – simply by driving just 10% less, or about 1,350 fewer miles each year. That achievement could cut total annual CO2 emissions in the U.S. by 110 million metric tons. That’s the same as shutting down about 28 coal-fired power plants for a year.

Driving less can make a big dent in carbon emissions, but the rise in electric vehicles also has the potential to make an impact in coming decades (if, that is, the electricity used is produced by zero-carbon or low-carbon sources of energy). As of 2018, more than one million electric vehicles were traversing American roads, and the market appears to be growing rapidly, according to a briefing from Consumer Reports. There are now more than 40 types of electric vehicles on U.S. roads, up from three in 2010. Luxury brands such as Jaguar, Mercedes, and Audi are planning to introduce electric car models to compete with Tesla, and more affordable options by Kia, Hyundai, and Nissan are now available.

Meanwhile, carsharing is gaining traction in some cities. Carsharing services such as Zipcar and car2gov are offering city dwellers easy solutions for quick trips. Other companies are populating city streets with fleets of electric scooters – although they’re clearly not well-suited for everyone. And carsharing hasn’t uniformly led to lower overall emissions, especially when the vehicles shared are powered by fossil fuels.

One development to keep an eye on is the Trump administration’s efforts to roll back fuel efficiency standards, and an apparent revolt against such deregulation by Ford, Volkswagen, BMW, and Honda. Those four automakers, representing 30% of new car sales in the U.S., have aligned with California’s progressive policies on fuel efficiency. Their effort is certain to face legal challenges from the Trump administration’s Justice Department, but the automakers’ pact with California, if it proceeds and succeeds, would set the goal of reaching an average fuel economy of 50 mpg by 2025.

Adding to growing uncertainties for automakers and their customers is the Trump administration’s mid-September 2019 effort to revoke California’s authority under the 1970 Clean Air Act to set motor vehicle emission standards more stringent than the overall federal standards. That provision over nearly five decades has been a critical feature of U.S. motor vehicle emission standards in and well beyond California, as more than a dozen other states have opted for the tougher California standards. While the Trump revocation initiative is certain to be challenged, with the eventual outcome perhaps not decided for a year or more, uncertainty about the future of auto emission standards is the only certainty.

The hidden costs of play – and of work

Along with daily driving, there is a steep cost to air travel – whether for work or play. Demand for jet fuel in the U.S. increased in 2018 – just one sign that air travel is a growth sector for sources of carbon emissions. Globally, airlines carried 4.3 billion passengers in 2018, contributing about 2% of global greenhouse gas emissions. By 2050, global emissions from passenger air travel globally are projected to increase by 300-700%, according to the European Commission.

A small but perhaps growing movement to cut back on air travel is taking hold in Europe and North America, and young climate activists such as Greta Thunberg from Sweden are helping to raise awareness of the health and ecological risks posed by climate change and of the contributions of the aviation industry. There’s even been a new term added to the climate change lexicon: flight shaming.

In June, Andy Newman of The New York Times wrote of the irony of people who are eager to visit places that are at risk of disappearing because of climate change – thereby hastening the demise of those places by flying there. In his piece, Newman cites a sobering statistic: 32 square feet of Arctic summer sea ice melts for every airline passenger who flies 2,500 miles.

Cruise travel, meanwhile, poses its own threats to the globe’s climate. The most efficient cruise ships emit three to four times more carbon emissions per passenger than commercial air travel.

Beyond vacation travel and tourism, another big source of carbon emissions from air travel is business trips. In 2018, U.S. travelers took 463.6 million business trips, and that number is forecast to rise to 493.7 million by 2022, according to Statista, a provider of market and consumer data. As businesses become more conscious of their impacts on the environment, and their bottom line, virtual business meeting platforms such as BlueJeans have become an alternative to air travel.

Academia, another source of air travel emissions, has also begun to grapple with its impact on climate change. There’s a worry among some, at least, that all those climate change meetings might be making climate change worse. One of the largest annual meetings for climate scientists in the U.S. – the fall meeting of the American Geophysical Union, routinely attracting more than 23,000 visitors from across the world – is among those beginning to grapple with just that issue.

More to read on transportation and climate change:

Current U.S. EPA page on transportation and climate change

Fast Facts: U.S. transportation sector greenhouse gas emissions 1990-2017

WHO web page on the climate impacts of transport

IPCC AR5 chapter 8 on global emissions from transport (2014)

Transportation Research Board, The National Academies (2012): Climate change and transportation

United Nations Conference on Trade and Development, May 2019: Why the transport sector needs to adapt to climate change

Transportation is the biggest source of CO2 in the U.S., Climate Central, Nov. 2017

IEA meeting, 2016: Life in the fast lane: evolving paradigms for mobility and transportation systems of the future

How your flight emits as much CO2 as many people do in a year, The Guardian, July 19, 2019

Cruise ship pollution is causing serious health and environmental problems, Forbes, April 26, 2019

Cargo ships are emitting boatloads of carbon, and nobody wants to take the blame, PhysOrg, Dec. 26, 2018

Editor’s note: This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story. (Minor edit made to article on 10/7/19.)