Energy by Part


The energy discussion so far has primarily been about how clean energy can replace fossil fuels to generate electricity for heating, cooling, lighting, and light-duty transportation. That part of the energy sector, however, accounts for only 25% of global GHG emissions. To really understand what we are dealing with here it’s necessary to look at all the sources of GHG emissions from the energy sector.

Net-Zero Emissions Energy Systems 1

The Hardest Emissions to Eliminate

Those energy sources highlighted as longer pie pieces


World-wide GHG emissions from the transportation sector account for about 14% of total emissions. According to the US EPA almost 95% of transportation energy comes from petroleum-based fuels, mostly gasoline and diesel.2

In the United States, though, the transportation sector is the largest source of CO2, accounting for 28% of GHG emissions. It has overtaken the generation of electricity as coal is replaced by renewables and natural gas. Light-duty (passenger) vehicles account for 60% of those emissions, 

We can expect the share of electric vehicles to grow, but it’s important to remember that the electricity they use is only as clean as the energy source used to produce that electricity. The variation among countries is dramatic. The total emissions per vehicle includes manufacture, fuel use at the power plant, and upstream fuel production. For electric cars, grid losses need to be taken into account.

Manufacturing emissions from petrol cars are assumed to be less than 60% that of electric vehicles (longer lifetime mileage and smaller manufacturing footprint.) All this taken into consideration, electric vehicle emissions range from similar to average petrol cars to less than half of the best hybrids depending on power source.3

Freight transport by road is responsible for a large share of GHG emissions and is particularly hard to decarbonize. Heavy-duty trucking uses about 50% of all diesel fuel and produces 80% of the global net increase in diesel since 2000. It is expected to double by 2050.4

In a recent report by the International Travel Forum (ITF) they say that “given the current state of research and commercial deployment no zero emissions solution in widespread use is foreseeable in the short to medium term for long-haul heavy freight trucks.”5

Decarbonizing the aviation sector will be even harder than heavy-duty trucking. This area will become more critical as incomes rise in developing countries and more people begin to fly. The best that can be hoped for between now and 2050 is the introduction of low-carbon fuels, but according to a report from the International Council on Clean Transportation (ICCT), “this seems very unlikely, if you consider everything that would need to happen to realize that vision.”6

Cellulosic biofuels represent the best replacement for aviation jet fuels, but their availability is subject to a complicated interaction that would require, among other things, the electrification of most cars and trucks.  It’s going to require broad climate mitigation across all energy sectors, and that is just not happening at this time.

GHG emissions from shipping account for slightly more than that from aviation. Projected emissions from maritime shipping will increase 23% from 2015 to 2035. A recent OECD report lists a set of three measures necessary to decarbonize shipping: technological, operational, and alternative fuels and energy. The report continues that utilizing these measures could make decarbonization of maritime shipping possible by 2035, but that market forces and regulation to accomplish this do not exist at this time.7

Many rail systems throughout the world are electrified, but in the US freight trains run on diesel. Electrification would be the obvious path to decarbonization, but it would be very costly. Electric vehicles and roadways would be another costly solution. Once again there is no public focus on developing the technologies to accomplish this.8 


Global Industrial Energy Consumption Forecast   2015 to 2050 by Fuel

While the energy and transportation sectors have seen progress in decarbonizing, the industrial sector, representing about 21% of GHG emissions, and including manufacturing, mining, construction, and agriculture has seen far less change.9 It uses more delivered energy than any other end-use sector, consuming about 54% of the world’s total delivered energy.10 As you can see from the chart above, there is little change within the sector expected for fuel type even as energy consumption grows.

If we distinguish between OECD and Non-OECD countries, we see two significant differences. By 2040, the Non-OECD countries  will be approaching 3 times the energy consumption of OECD countries in this sector, and coal will continue to provide a large part of that increased energy demand.

Manufacturing is the largest emitter of the group and can be further broken into 5 main categories: paper, food, petroleum refineries, chemicals, and metal/mineral products. Steel, cement, and petrochemicals are all very carbon-intensive processes. For decades the industrial sector has been pouring carbon emissions into the atmosphere, reaching a cumulative total of 1.3 trillion metric tons in 2014.11

Steel production accounts for 6.7% of global CO2 emissions, most of it coming from the Basic Oxygen Furnace (BOF) which still dominates global production. China has dominated production and consumption of steel since the beginning of the century. The electric arc furnace (EAF) has gained widespread use in the US as the industry has declined. The EAF uses large amounts of electricity which could be produced by renewables. 

China continues to rely on coal to fire its steel plants and will dictate the rate of change to clean energy sources. As with their power facilities, these plants are relatively new and not likely to be replaced in the near future. And, as with cars, even if China were to use more EAF plants, the emissions from such plants would not be any better than the source used to produce the electricity needed.

Research is ongoing to develop new production techniques because the continued use of BOF plants will make zero-emissions impossible to achieve in this sector.

Cement production: “Concrete is tipping us into climate catastrophe. It’s payback time.”12

In a Guardian article from February 25, 2018, Jonathan Watts lays out the horrific numbers regarding concrete. After water, it is the most widely used substance on earth, and represents in the most dramatic terms the human endeavor to tame nature. Concrete has been used since Roman times, but its central function in modern construction dates more recently from the mid-18th century.

Concrete is composed of cement, water, sand, and gravel, the cement acting as a bonding agent for the mix. Each year, more than 4 billion metric tons of cement are produced, accounting for about 8% of global CO2 emissions. On a business as usual path, cement production is eventually expected to surpass 5 billion metric tons per year.13

After energy generation and transport, cement manufacture is the next biggest producer of GHG emissions. CO2 is produced from two parts of the cement production cycle, first from the mostly coal burning to produce the heat necessary and second from the thermal decomposition of calcium carbonate.14 

In 2015, cement production produced around 2.8 billion metric tons of CO2. Reducing cement production emissions is considered difficult because 50% of those emissions are produced by a chemical reaction. The other half are 40% fossil fuel burning and 10% from fuels to mine and transport the raw materials.

With so much construction predicted in the developing world in the decades to come, it’s important to limit the emissions from this process. There are signs that Chinese consumption may be leveling off, but India is set to rapidly urbanize and build the necessary infrastructure to support this new construction. Other developing countries will further contribute to this ongoing increase in demand.

What can be done? CO2 intensity of cement production has decreased, but emissions continue to increase with demand. More efficient kilns could lower the global average with best practices by another 20%. Replacing coal with alternative energy sources could also contribute to lower carbon emissions. Finally, “high blend” cements in which part of the clinker is substituted with other materials, can reduce emissions per kilogram by a factor of four. This is referred to as adjusting the “clinker ratio” but is not possible in all situations because of change to the quality of the cement.15

The carbon footprint of the cement industry is so large that without changes, it could jeopardize the goals of the 2015 Paris Accords by itself. The industry hopes for technological fixes like Carbon Capture and Storage (CCS) but it is not yet (if it ever will be) commercially available. Unless the industry is forced to internalize its environmental damages, it will continue emitting an additional 500 million metric tons of GHG emissions per year for decades to come.

Load Following Electricity

As renewable energy has become more available and in use at power plants, the intermittent nature of their power production has created a need for a type of power that can be produced to balance out the power supply. The power plants which fill this function are referred to as “load following.” The electricity produced by these plants is less efficient and more expensive than that from base load plants.

Power output throughout the day must also contend with variability in demand. Load following power plants are operated to respond to this variability. They can be hydroelectric, diesel and gas engine power plants, natural gas, or heavy fuel oil. As noted above, they account for a significant part of global fossil fuel emissions.