On the current trajectory, greenhouse gas emissions from cars, trains, ships and airplanes may become one of the greatest drivers of human-induced climate change, according to a draft of the forthcoming U.N. fifth assessment report on mitigation of climate change.
Authors project with high confidence that continued growth in emissions from global passenger and freight activity could "outweigh future mitigation measures," says a preliminary version of the Intergovernmental Panel on Climate Change (IPCC) study obtained by ClimateWire.
Lacking improvements in fuel efficiency combined with a comprehensive mitigation policy, the report finds that transport emissions could double by 2050 from 6.7 gigatons of emitted carbon dioxide in 2010, which represents 22 percent of the world's total.
Demand for personal vehicles and consumer goods in fast-growing economies like China, India and Brazil is fueling the use of motorized transport across all modes. The transportation sector's almost complete reliance on energy-dense, high-carbon fuels, like gasoline and diesel makes reducing emissions an even greater challenge.
"[Transportation] could actually become one of the biggest sectors of emissions ... because you can mitigate the other sectors more easily," said an expert familiar with the draft report.
The electricity sector can reduce emissions relatively easily by adopting renewables like solar and wind, while cars and trucks can't harness these zero-emissions energy sources without sophisticated and expensive energy storage technologies.
But the report adds that there are still opportunities for change.
Could cities be part of the solution?
The upcoming report finds that technical improvements and behavioral changes, combined with new infrastructure and urban development investments, could reduce energy demand from the transport sector by up to 40 percent below the base line in 2050, a greater reduction potential than shown in the fourth assessment report.
According to transport exports, urban centers represent both the greatest potential source of transport emissions and the greatest opportunity to mitigate them.
"We're at a really important crossroads," said Manish Bapna, executive vice president of the World Resources Institute, on a recent call with reporters. "Will cities be part of the solution or the problem?"
According to the World Health Organization, the urban population will double from 2.5 billion in 2009 to nearly 5.2 billion in 2050. In China alone, 300 million people are expected to move into cities over the next 15 years.
Building cities in a way that slows vehicle demand while delivering high accessibility could prove to be a low-cost option for curbing greenhouse gas emissions, as well as a solution to pressing problems for policymakers like local air pollution and poor public health.
Addressing transport emissions in a more comprehensive manner through urban design is one of the main themes at the U.N. World Urban Forum being held this week in Medellin, Colombia.
"We are already struggling with the number of cars we have in the streets of our cities; congestion, air pollution, road safety issues, health impacts from people driving all the time," said Luc Nadal, technical director for urban development at the Institute for Transportation and Development Policy (ITDP). "This is an absolutely unsustainable development model."
Unsustainable habits and designs
Motorized transport makes up almost a quarter of global man-made emissions, most of which stem from personal vehicles. Nadal said it would be "an absolute disaster" if the 20th century model of car-centric transport development, which has characterized many cities in the United States and Europe, were to continue into the 21st century.
"The way buildings are built, the streets are laid, urban forms that will be with us for a long, long time, decades certainly, centuries probably. We have streets in some places that are several millennia," he said. "Once these patterns are on the ground, it's very difficult to change them."
ITDP today unveiled a new policy guide at the Urban Forum to evaluate real estate developments that integrate sustainable transport and land-use planning to connect people conveniently and safely to jobs, education, shopping and other opportunities.
The TOD (transit-oriented development) Standard is based on eight elements: walkability; bicycle-friendliness; a connected network of streets and paths; a robust transit system; a balanced mix of activities; dense, vertical building; compact development; and a shift away from personal motorized transport.
These principles are understood by urban planners and architects, but policymakers still lack awareness of them, said Nadal. In rapidly urbanizing parts of Africa, Asia and Latin America, cities are still being built to accommodate motorists, even where they represent a fraction of the urban population.
The IPCC draft report finds that institutional, legal, financial and cultural barriers may limit the adoption of low-carbon transport technologies and changes in transport demand. A comprehensive analysis on the extent to which these barriers can be overcome is outside the scope of the report.
A final version of the complete IPCC study is set for release Sunday.