We talk a lot about decarbonization in the electric power sector, possibly because there are so many solutions on the table: nuclear reactors, renewable energy, carbon capture, and on and on. But electricity is only about one-fifth of global final energy consumption, and decarbonization outside the power sector is pretty disappointing. If we want to really tackle the emissions challenge, we’ll need innovation and deployment of technological options far beyond zero-carbon power generation.
As the figures below illustrate, the carbon intensity of energy — that is, total carbon dioxide released into the atmosphere for every joule of primary energy — went up by 3% for industrial energy inputs and 2% for the commercial and service sector between 1992 and 2015. Transportation and agricultural carbon intensity were essentially flat.
There are three basic factors that govern overall emissions: the carbon intensity of energy, the energy intensity of economic activity, and overall economic activity. Restricting economic activity is a non-starter politically and socially. Energy intensity of the economy tends to decline steadily, though there are no clear ways to dramatically accelerate that trend. This leaves the carbon intensity of energy as a major point of intervention, by deploying low-carbon energy sources to replace high-carbon sources. Unfortunately, so far this has barely been happening. Let’s examine the trends in each of the world’s major energy sectors.
A major reason that industry moved backwards is the trend toward using more coal (growing from 22% to 27% of the total, including energy inputs for feedstock rather than combustion, but not counting upstream coal for electricity).
It is little surprising that transportation carbon intensity barely budged, since the share of petroleum products in the sector barely fell (from 94% in 1992 to 92% in 2015). Electric vehicles have started to gain real traction in the last few years, but mostly for light-duty vehicles and only in certain markets.
In the residential sector (the most successful sector in decarbonizing energy), biomass fell, from 42% to 36% of energy input, as did coal, from 8% to less than 4%. In addition to being a source of greenhouse gas emissions, direct burning of biomass is the leading source of indoor air pollution, and energy modernization is as much about a high standard of living as it is about environmental quality.
The situation in the world commercial sector is more mixed, with electricity growing in share (40% to 51%) but natural gas decreasing (27% to 24%). Agricultural energy (excluding upstream inputs such as fertilizer and pesticide) became a fraction of a percent more carbon intensive, with more electrification (19% to 26%) and less petroleum (65% to 55%).
The carbon intensity of the world energy supply is essentially flat, and in the case of industry and commerce, increasing. Furthermore, industry is the largest sector at 37% of total final energy consumption. Overall, the world energy system reduced its carbon intensity by a tenth of a percent in over 20 years.
As recently demonstrated by UC Irvine’s Steve Davis and his coauthors, we still do not have good low-carbon solutions for many important energy services, particularly outside of electricity. In the iron and steel sector, which constitute 5% of the world’s total energy usage, 64% of the energy input is in the form of coal, not including coal in electricity, and there are no low-carbon steelmaking processes that have been demonstrated to work economically at scale. Aviation accounts for 3% of energy usage, and world air travel could triple by 2050 without yet a demonstrated scalable low-carbon solution.
Even where we do have tools to cut emissions, there are a host of economic, technical, and political barriers to doing so. Without massive deployments of grid-scale batteries and/or high voltage direct current transmissions, the power grid will struggle to support high volumes of renewable energy. Likewise, while many countries and regions around the world are exploring ways to decarbonize personal automobiles through legislative fiat, the technology to do so remains nascent and will take decades to deploy.
What can we expect in the coming years? The International Energy Agency’s World Energy Investment 2018 shows that overall worldwide energy investment in the energy industry fell in 2017, including in renewables, nuclear power, and industrial energy efficiency. World investments in research and development, both public and private, received welcome but modest increases in 2017. These trends do not instill great confidence that the pace of world decarbonization is going to accelerate. The onus is on political and business leaders to make the investments required — ranging from preserving existing nuclear plants, deploying developed clean energy technologies, bringing emerging technologies to market, and developing solutions for the difficult-to-decarbonize sectors — to accelerate world decarbonization, or it will not happen.