What Is a Carbon Footprint? What It Means and How to Reduce Yours

You are not imagining it: the Earth is running a fever. Droughts, wildfires, frequent heat waves — if you are not experiencing them where you are, you are certainly seeing more of them in the news. According to the National Centers for Environmental Information, the year 2020 was the second warmest on record after 2016, with seven of the Earth’s warmest years occurring after 2014.

The increase in the average global temperature is caused by the increase of greenhouse gases in Earth’s atmosphere. “The atmosphere lets energy from the sun pass through, but greenhouse gases absorb and trap energy that the Earth would normally emit to space, leading to more energy and higher temperatures,” says Benjamin Cook, climate scientist, author of Drought: An Interdisciplinary Perspective and Associate Research Professor at Columbia University’s Earth Institute.

The carbon dioxide level in the atmosphere is considered the “biggest control knob for Earth’s thermostat,” says Cook, which is why the concept of a “carbon footprint” has become increasingly important in conversations around global warming and climate change.

What does “carbon footprint” mean?

Our carbon footprint is the total amount of carbon we all collectively emit due to all human activities. Currently, the world produces carbon emissions equivalent to about nine gigatons (billion tons) of carbon dioxide each year. About half of these emissions are absorbed by the oceans and terrestrial biosphere, leaving an excess of about four gigatons of carbon dioxide to accumulate in the atmosphere.

According to the Environmental Protection Agency (EPA), the United States produced about 6.6 billion tons of carbon dioxide equivalent in 2019. While the world average for personal carbon footprint is about six tons of carbon dioxide per person per year, the United States is the third highest in the world with about 20 tons of carbon dioxide per person per year, behind Australia and Saudi Arabia, according to University of Berkeley’s climate science research.

The biggest contributors to carbon emissions in the U.S. are:

• Transportation: 29%
• Electricity generation: 25%
• Industrial activities: 23%
• Commercial and residential heating: 13%
• Agriculture: 10%

(Graph by Robert Simmon, using data from the Carbon Dioxide Information Analysis Center and Global Carbon Project.)Getty Images

What effect does our carbon footprint have on the environment?

Earth’s warming trend has set off a cascade of climate events which include:

1. Drier soils: Global warming is not even across the Earth due to differences in heat capacities of land and water. Land surfaces are warming faster than water surfaces, and as a result soils are drier than usual. This affects vegetation growth and also makes wildfires spread more easily according to the National Aeronautics and Space Administration, NASA.
2. Warming oceanic temperatures: While the ocean can hold more heat under its surfaces than land can, it eventually reaches the surface and results in high ocean surface temperature anomalies. Among other effects, warming sea temperatures are detrimental to the fish species and can cause bleaching of coral reefs.
3. Acidification of oceans: As we pump more and more carbon dioxide into the atmosphere, the oceans have been absorbing this excess, making them more acidic. This has direct consequences on the health of all marine species but particularly for coral reefs, which can’t build their skeletons, as well as clams, mussels and sea plankton, whose protective shells can’t form under acidic conditions.
4. Loss of ice reserves and rising sea levels: Referred to as polar amplification, the warming trend is uneven across the different latitudes. Northern latitudes and the North Pole are heating up faster than the rest of the world and this has resulted in the decrease of snow cover duration on land, as well as arctic sea ice and mountain glacier volumes. The melting of the ice reserves coupled with the thermal expansion of the upper ocean due to warming has resulted in the continuous rise of the sea levels, according to NASA. Current sea levels are about 7-8 inches higher than when compared to their levels in 1900, with the last three inches of rise happening since 1993. This trend increases the risk of flooding of coastal areas during extreme weather and may lead to permanent changes to our coastlines, disrupting settlements and resulting in economic losses.

Currently, we are about 1.1 °C above pre-industrial temperature levels and are likely to surpass the 1.5 °C limit that was set as a goal within the Paris Climate Accord. This international treaty on climate change, adopted in 2015 by 196 countries, was the first binding agreement to bring all nations together to combat climate change. Each nation is expected to commit to ambitious national goals to reduce greenhouse gases as well as collaborate internationally to build resilience to adapt to rising temperatures.

According to the Intergovernmental Panel on Climate Change (IPCC), about half of the cumulative carbon emissions in the last 150 years have occurred in the last 40 years. “Depending on the trajectory we take over the next century, we will likely end up with 2-4 degrees of warming by 2100,” adds Cook. Translation: We need to accelerate our transition to renewable energy sources even faster than proposed based on the 1.5 °C goal.

While carbon emissions in 2020 fell about 10% due to the pandemic-related economic downturn, it hardly put a dent in the accumulation of the carbon dioxide in our atmosphere. Carbon dioxide does not dissipate or break down and stays put for hundreds of years. That means even if we could somehow stop all of our carbon emissions today, it would take over a decade to reverse the warming trend we are in.

What are some examples of my personal carbon footprint?

First, lets address the concept of a “personal carbon footprint” — the idea was popularized as part of a greenwashing campaign by petroleum companies, according to Cook. “This was a strategy to shift responsibility to individuals, rather than address the systemic nature of our global dependency on fossil fuels,” says Cook. He advises against solely focusing on one’s personal carbon footprint, since addressing climate change requires “a wholesale, systemic shift in our energy systems, something that is unlikely to happen through individual action alone.”

That said, from the electricity you use at home to the type of meals you put on the table, it’s true that everyone contributes to the world’s total carbon output. Your individual carbon footprint, however, is largely pre-determined. Here are the factors that matter most:

• Where in the world you live (specifically, which country and its energy sources and policies)
• Your socioeconomic conditions (more purchasing power means more goods manufactured and energy consumed)
• How energy intensive your lifestyle is (think access to heat, hot water and air conditioning)

How can I calculate my carbon footprint?

Carbon footprint calculators can help you better understand your individual contribution to the global carbon footprint. They typically take into account your impacts due to home energy use, transportation, waste generation and your diet (meat- or plant-based). Expect to input data such as your zip code, how many live in your household and what type of housing (single family home or apartment building) you reside in.

Some carbon footprint calculators are more elaborate, like the EPA’s calculator which requires much more detailed data, like type of fuel source used in heating your home, the price of your electricity bill, how many vehicles you own and how many miles you drive, as well as how much is recycled in your household. While these calculators will only reveal approximations of your carbon footprint, they can help pinpoint where individual impacts lie.

Can I reduce my carbon footprint?

Addressing global scale reductions in greenhouse gas emissions requires huge shifts away from fossil fuel use towards zero carbon energy sources, and each country needs policies to incentivize this transition. Perhaps one of the most impactful things individuals can do is organize and pressure their governments for swift action.

In addition, there are sustainable lifestyle choices we can all make to help along with achieving net-zero carbon emissions by 2050, which is what scientists believe is needed to curb global warming as close to the 1.5 °C limit set by the Paris Climate Accord. Here are some examples of how to lower your carbon footprint, all with varying degrees of impact:

• Limiting the size of your family (highest)
• Living car-free (high)
• Switching to a plant-based diet (high)
• Recycling (moderate)
• Upgrading light bulbs (low)

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