Sources of GHGs and Ways to Reduce Them

In 1987, the United Nations defined sustainability as “meeting the needs of the present without compromising the ability of future generations to meet their own needs.” In 2005 the acronym ESG – Environmental, Social Responsibility, and Governance – was coined and in many conversations is interpreted to mean ‘environmental sustainability.’ However, ‘environmental’ is just one of the three pillars of ESG.

By Tim Goedeker

What are GHGs?

Greenhouse gases (GHGs) are gases that absorb and emit radiant energy, within the thermal infrared range, that cause the ‘greenhouse effect’ (envision a greenhouse for plants, fruits, and vegetables). The primary GHGs in our Earth’s atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Greenhouse gases are not bad by nature. Without greenhouse gases, the average temperature of Earth’s surface would be about -18 °C (0 °F) rather than the present average of 15 °C (59 °F).

Greenhouse gases are generated from nature and mankind also known as anthropogenic GHGs. The key anthropogenic (man made) GHGs of focus are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).

Sources of GHGs

In 2000, see Figure 2, the top five countries/regions emitted ~50% of the World’s GHGs. (US, China, the EU, Russia, India).

In 2020, these same 5 countries/regions emitted ~54% of the World’s GHGs (China, US, India, the EU, Russia) which included a doubling of China’s & India’s share of the total and approximately 1/3 reductions in both the US and the EU’s share of the total.

Figure 3 shows the contribution (in %) of the key sources of GHGs for China, the US, the EU, India, Russia, and the rest of the world countries. As can be seen from the data, there is not one common solution to mitigate all GHGs. There will need to be a host of mitigation tactics across each source of GHGs.

In most countries/regions GHGs from electricity & heat (power) generation is the largest source, while the 2nd largest source varies by country/region. However, mitigating GHGs from power generation will address 25%-50% of the world GHG emissions.

Figure 4 uses the same data from Figure 3 but shows the contributions (in %) of GHGs from China, the US, India, the EU, Russia, and the rest of the world (ROW) for each of the key sources of GHGs. This provides a look at the country/region with the largest impact on each of the key sources of GHGs.

From this view, the greatest opportunity for GHG reductions is in the key sources:
• Power Generation (Elect / Heat) –China
• Agriculture – Globally
• Transportation – Globally
• Industrial Operations (Industry) –China
• Buildings – Globally
• Fugitives – China, Russia

Opportunities for GHG reduction in each of the key sources (Heat/Elect, Agriculture, Transport, Industry, Buildings & Fugitives) are addressed in the following paragraphs.

Power Generation (Elect/Heat)

With approximately 32% of the World GHGs coming from power consumption (elect/heat) improving energy efficiency (energy per unit GDP) should be a national priority among all countries.

By 2050, power consumption (elect/heat) is forecasted to increase by 50%, equivalent to adding 7 billion metric tonnes of GHG (assuming current power generation GHG emission rate), which includes a nearly tenfold increase in wind and solar energy generation (50 million GWh).

Options to reduce power generation emissions of GHGs include changing high GHG emitting feedstocks (coal, oil) to lower or no GHG emitting feedstocks (natural gas, wind, solar, nuclear, hydro). However, the lower or no GHG sources of power generation have limitations.

“Intermittent” power generation from renewable solar & wind sources do not produce power 24/7/365. To ensure reliable power 24/7/365 additional sources of power (batteries, natural gas, etc.) are needed to supplement wind & solar sources.

“Intermittent” power generation from solar & wind requires a lot of land. Nearly 5,000-10,000 acres per Gigawatt (~3-6 hrs peak sun per day) are required for solar generation and approximately 50,000-80,000 acres per Gigawatt (~6 hrs peak wind per day) for wind generation.

GHGs Consist Of:

CO2: ~80% of GHGs (global warming potential (GWP) is 1) CH4: ~10% of GHGs (GWP is 25x CO2 or 25 CO2e)
N2O: ~7% of GHGs (GWP is 298x CO2 or 298 CO2e)
*1 Billion metric tons = 1 Gigaton

Sources of Global Anthropogenic (man-made) GHGs – ~49 B metric tons (MT) – 2018

~76% – Energy Use (~37 B MT)
• 32% – Heat / Elect generation (~15 B MT)
• 14% – Transportation exhaust (~7 B MT)
• 13 % – Industrial combustion (~6 B MT)
• 6% – Residential / Commercial buildings (~3 MT)
• 6% – Fugitives (leaks) (~3 B MT)
• 5% – Bunker fuel & other combustion (~3 B MT)
~15% – Agriculture and Land Use (~8 B MT) ~6% – Industrial Processes (~3 B MT)
~3% – Waste (~1 B MT)