Major reductions in greenhouse gas emissions require comprehensive changes not just in how we source energy, and manage forests and agricultural systems, but also in how we live and move in urban areas, where most of the world’s energy, materials, and products are consumed.

Decarbonization Pathways

To decarbonize we must comprehensively shift energy sourcing from dirty to clean; rethink forest and agricultural systems management; focus on how human beings live and move in urban areas; and address consumption and waste. The main pathways to a low-carbon future, referred to as the deep decarbonization pathways, or DDPs, are:

• Conservation & Efficiency—Consuming less energy and using energy more efficiently in buildings, transportation, and industry.  
• Decarbonization—Removing coal and natural gas from the electricity grid entirely; limiting the use of natural gas in heating and transportation in the 2030-35 time frame; and getting to zero-carbon fuels by 2050.  
• Fuel-Shifting—Switching fossil fuels to low- or zero-emission renewable fuels to power buildings, vehicles, and industry.  
• Waste Reduction—Reducing the emissions associated with all waste products, as well as decreasing consumption in general.  
• Emission Sequestration—Preserving and increasing natural carbon sinks, such as forests, agricultural land, vegetation, and soils.  
• Methane Emission Reduction—Reducing methane emissions from landfills, coal mines, and agriculture and halting all new natural gas and oil development.  
• Carbon Capture and Sequestration—Deploying systems to capture carbon emissions at smokestacks or directly from the atmosphere.

Sectors to Decarbonize

There are six key sectors in which to concentrate decarbonization efforts: (1) Energy supply; (2) Transportation (air, marine, fleet, freight) (3) Residential and commercial building; (4) Industrial (manufacturing, construction, agriculture energy transformation, mining); (5) Agriculture and waste; (6) Land use and forestry. Each of these has a series of critical transitions or actions that need to occur as follows:

Energy Supply Sector: Ultimately, the electricity grid needs to be as close to 100% clean and deeply efficient to enable increased electricity generation to power as many vehicles, buildings, and industrial processes as possible, and upgraded to enable variability in transmission and a free-flow of electrons from generation to source.

First efforts must focus on ramping up energy efficiency to decrease the amount of energy required, thereby stretching existing resources as far as possible, and obviating the need for new fossil-fuel powered supply. Equally important are new business models that will transform utilities and power markets to accommodate decarbonization.

Coal and natural gas must be replaced with renewable energy to reduce fossil fuel emissions and decarbonize electricity generation, while electricity grids must also be modernized to integrate renewable energy and resources that control energy demand.  

Transportation (air, marine, fleet, freight) Sector: For the transportation sector, the focus is fuel-switching: electrified or hydrogen-powered public transit, high-speed rail, bicycling, and walking, using biofuels for aviation and possibly compressed natural gas for long-haul freight or liquified natural gas for marine.

As with the energy supply, we also must focus on efficiency by improving fuel efficiency and engine efficiency to decrease the need for energy. Transport vehicles must be electrified as much as possible to take advantage of an increasingly clean electric grid. Fuel cell vehicles may also need to be part of the mix of options to replace gasoline-powered, internal combustion engines.

For vehicles that cannot be electrified (airplanes, long-haul trucking, and marine vessels), their liquid and gas fuels must be decarbonized as much as possible. Finally, vehicle miles traveled must be reduced as much as possible and replaced by low- or zero-carbon alternatives, such as electrified public transit, high-speed rail, bicycling, and walking.

Residential and Commercial Sector: The key actions for decarbonizing buildings are deep energy efficiency, energy conservation, and switching from coal, oil, or gas as the fuel for space and water heating. Buildings should also be able to store energy, produce energy (solar panels on their roofs would be an example), and house electric vehicles that would also be able to store energy in their batteries.

Industrial (manufacturing, construction, agriculture energy transformation, mining) Sector: For industry, again energy efficiency is crucially important, as well as using onsite energy management systems such as combined heat and power to capture and reuse waste heat. As with vehicles, switching to lower-carbon fuel sources and clean electricity for industrial processing is also required.

Agriculture and Waste Sector: The agriculture sector requires both reducing harmful methane emissions that come from land and agriculture uses, as well as decreasing nitrogen in fertilizers while increasing nutrients in carbon-capturing soil and developing processes that will convert manure to energy to power farm operations. Soil and agriculture play a crucial role in sequestering carbon, so protecting farmlands and nurturing soils to maximize carbon capture is required.

Required actions include: reducing harmful methane emissions from land, agriculture, and animals; decreasing nitrogen in fertilizers; increasing nutrients in carbon-capturing soil; developing processes that convert manure to energy to power farm operations; and electrifying farm equipment and using onsite renewable energy generation on farms.

Land Use and Forestry Sector: As with agriculture, forests are critical carbon sinks and as such must be both maintained but also increased significantly. Not only must deforestation end, but reforestation and afforestation are essential. Logging must be curtailed and forests cannot be converted into development. Attention must be paid to increase the carbon sequestration potential of lands and natural areas in urban areas for their carbon sequestration and heat-cooling value.

For a list of studies, books, reports, and articles to gain a better understanding of what it takes to achieve deep decarbonization, please review this reference guide.