What Are the Top Sources of CO2 Emissions Worldwide?

This article is an excerpt from the Shortform book guide to "How to Avoid a Climate Disaster" by Bill Gates. Shortform has the world's best summaries and analyses of books you should be reading.

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What are the top sources of CO2 emissions worldwide? What are the main challenges with reducing global carbon emissions?

In his book How to Avoid a Climate Disaster, Bill Gates divides the major sources of carbon dioxide emissions into five categories. These categories (and their corresponding percentage of overall emissions) are manufacturing (31%), electricity generation (27%), agriculture (19%), transportation (16%), and heating and cooling (7%).

In this article, we’ll examine Gates’s commentary on the current state of each category and some significant challenges and opportunities for curbing emissions. 

Manufacturing (31%)

Gates explains that the cement and steel used to build infrastructure are the primary sources of CO2 emissions in the manufacturing category. Producing one ton of cement and one ton of steel generates one and 1.8 tons of carbon dioxide, respectively, and the world uses a lot of them. For example, the United States produces 600 pounds of cement and 600 pounds of steel per person every year, and between 2001 and 2016, China used nearly 26 billion tons of cement alone. The quantity of these materials that go into constructing roads, bridges, and buildings make them major greenhouse gas sources.

Reducing cement and steel emissions is problematic because the technology for carbon-less manufacturing on a large scale doesn’t exist yet. Still, the demand for these building materials will increase as the global population grows. Gates explains that our most viable yet imperfect option is to keep the process roughly the same but capture the carbon dioxide before it reaches the atmosphere. Unfortunately, while this technology exists on a relatively small scale, it can’t capture all the carbon dioxide emitted, and it makes both the manufacturing and the final products more expensive. Since the options for carbon-less manufacturing are limited, using materials as efficiently as possible and recycling materials is especially important.

Electricity Generation (27%)

According to Gates, generating electricity without emitting carbon dioxide is the most critical step to eliminating carbon emissions because non-carbon electricity can also help reduce emissions in all other categories. For example, electric cars reduce emissions in the transportation category, and electric heat pumps can reduce emissions from furnaces in the heating and cooling category. As of 2021, fossil fuels account for two-thirds of electricity production worldwide, with hydropower contributing 16%, nuclear 10%, and renewable sources (including solar and wind) 11%. Gates highlights solar and wind as promising renewable/non-carbon energy sources. We’ll briefly discuss each. 

Solar Power

Solar is one of the most widely used and growing renewable electricity sources. Solar has obvious appeal in that the sun is an unlimited source of energy, and solar panels can be scaled up to industrial size and down to individual homes and businesses or even tiny cells that can charge a single device. However, Gates notes that solar also has significant limitations, including:

Efficiency. Gates explains that at current efficiency levels, solar takes up between five and 50 times more space than fossil fuels. This limitation is especially significant considering that land devoted to solar energy production won’t be available for other uses like farming and housing. 

Discontinuous Availability. Gates notes that one of the biggest challenges in carbon-less electricity generation is the public’s expectation that electricity will be reliably available 24/7. Unlike fossil fuels that generate energy day or night, solar panels only produce electricity when the sun is shining, meaning less power is available at night, during long or especially heavy storms, and during winter. 

The challenges of discontinuous solar availability add to the complexity of a large-scale switch to solar. For example, Gates notes that it isn’t feasible or economical to use existing battery technology to store the huge amounts of energy cities would need during especially dark periods. Additionally, the uneven distribution of sunlight throughout the year creates the problematic question of whether to invest in enough solar panels for the winter (in which case you’d have too much power during the summer) or summer (in which case you wouldn’t have enough power in the winter). 

Technology coupled with strategic pricing can help address the challenges of discontinuity. For example, “smart homes” could be outfitted to use electricity to charge electric vehicles, heat water, and perform other tasks during off-peak hours, such as late at night. Additionally, Gates notes that utility companies could start charging more for electricity during peak hours to create an incentive for people to restructure their energy use based on availability. 

Wind and Offshore Wind 

Wind-generated electricity faces many of the same challenges as solar. Gates notes that windmills take up ten times more space than solar and have similar reliability challenges (the wind doesn’t always blow). Additionally, Gates explains that the lengthy and complex permitting process for installing offshore wind turbines in the United States is a deterrent to widespread adoption. 

Another challenge facing wind and solar power is that they’re location-specific, whereas fossil fuels can be shipped and used anywhere. Making a significant switch to wind or solar would necessitate a large-scale and coordinated update of electrical grids and power companies so that renewable energy generated in one location could be used in another. However, this would also necessitate crossing state or even national boundaries, adding political and economic complexity to the task. Fossil fuels, on the other hand, are easy to transport and our existing infrastructure is set up for their transport and use.

Nuclear Energy

While Gates advocates pursuing and improving all of the renewable energy sources discussed above, he notes that our best chance of achieving non-carbon electricity generation is to combine the above options with nuclear power. This would provide many benefits:

  • Reliable and consistent electricity generation: Nuclear doesn’t have the discontinuity problems solar and wind face.
  • Non-carbon fuel source: Nuclear reactors run on uranium, a non-carbon and relatively abundant fuel source.
  • Less material-intensive to build: Nuclear reactors are the second-most materials-efficient type of power plant we can build, bested only marginally by natural gas. Therefore, making the reactor itself emits less carbon dioxide than other energy sources.   

Gates recognizes public hesitancy to pursue large-scale nuclear power due to the dangers of radioactive waste, the potential for a nuclear reactor meltdown, and uranium’s role in producing weapons of mass destruction. However, he notes that the idea that nuclear is an unsafe option is flawed. Nuclear power has resulted in fewer deaths per unit of energy produced than coal, oil, biomass, or gas. Additionally, Gates notes that new technology promises to make nuclear meltdowns a near impossibility. Therefore, he explains that reducing the threat of global warming will likely necessitate a more widespread acceptance of nuclear power. 

Agriculture (19%) 

Raising livestock generates most of the emissions in the agriculture category. Animals such as cows, sheep, and goats generate methane in their flatulence, and animal manure (particularly pig manure) generates nitrous oxide. Both of these greenhouse gases have far more warming potential than carbon dioxide. Additionally, when we clear land for livestock the carbon stored in the trees and disturbed soil is released into the atmosphere as carbon dioxide. 

As people around the world become wealthier, their dietary preferences shift toward consuming more animal products, driving up the carbon footprint of their diet. This trend, combined with global population increases, will substantially increase the demand for animal-based food. As a result, if current trends hold, emissions in this category may increase by two-thirds in the coming decades. While Gates doesn’t expect people to give up meat entirely, he encourages readers to eat fewer animal products to help curb greenhouse gas emissions.  

Transportation (16%)

Transportation accounts for 16% of emissions worldwide, but Gates explains that it’s the biggest source of emissions in the US, with roughly half of those emissions coming from personal vehicles. Without a large-scale shift to electric cars and carbon-less electricity to charge those cars, we can expect emissions from personal vehicles to increase as car ownership becomes more common globally. 

The two most significant barriers to reducing personal transportation emissions with electric cars are the availability of carbon-less electricity (if we use fossil fuels to generate the electricity used to charge the car then we’re just swapping one fossil fuel for another) and the purchase cost of an electric vehicle. However, Gates estimates that the price of an electric car will be similar to the price of a gas-powered car by 2030, and sooner should gas prices increase.

Nearly a third of the remaining global transportation emissions come from large trucks and buses, as well as another 10% from cargo and cruise ships and 10% from airplanes. Unfortunately, these larger vehicles are more difficult to electrify because current battery technology is 35 times heavier than gas and would require vehicles to make frequent recharging stops. The resulting loss of efficiency makes current battery technology impractical for large vehicles. Gates notes that nuclear-powered ships are a carbon-free option and cites advances in alternative fuels as a promising solution for trucks and planes.

Heating and Cooling (7%)

Heating and cooling technology improves people’s quality of life in moderate temperatures and can be the difference between life and death in extreme temperatures. Gates expects the global demand for air conditioning to triple by 2050 as wealth increases in emerging economies and extreme heat becomes more dangerous. Ironically, the more the planet warms, the more air conditioning people will use, further exacerbating global warming (this is another reason Gates stresses the need for carbon-less electricity). 

Efficiency can help curb emissions in the heating and cooling category. Gates estimates that emissions from air conditioners could be reduced by half if people purchased the most efficient models available. Additionally, since most furnaces and water heaters currently run on fossil fuels, Gates suggests switching to electric heat pumps as another way to increase efficiency and reduce emissions. However, since a new furnace or water heater is an expensive and infrequent purchase, he notes that this large-scale switch is likely to take a long time without compelling consumer incentives. 

What Are the Top Sources of CO2 Emissions Worldwide?

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Darya Sinusoid

Darya’s love for reading started with fantasy novels (The LOTR trilogy is still her all-time-favorite). Growing up, however, she found herself transitioning to non-fiction, psychological, and self-help books. She has a degree in Psychology and a deep passion for the subject. She likes reading research-informed books that distill the workings of the human brain/mind/consciousness and thinking of ways to apply the insights to her own life. Some of her favorites include Thinking, Fast and Slow, How We Decide, and The Wisdom of the Enneagram.

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