It isn’t easy to estimate which trees absorb the most CO2. To calculate this average, we have to consider the composition of the forest. Forests with various species should be favored because they absorb more CO2.

On average, a tree absorbs about 25kg of CO2 per year. Depending on the tree, the range ranges from 10kg to 40kg per year. A tree also stores approximately 167 kg of CO2 annually (1 ton of carbon dioxide annually for six mature trees).

Carbon absorption capacity varies depending on several factors like tree species and size. Let’s understand the contribution of trees to climate change and the process of absorbing CO2 deeply.

How Much CO2 Do Trees Absorb Globally Annually

Trees are well down to as “carbon sinks.” It is accomplished through the process of photosynthesis. Trees absorb carbon dioxide through their leaves and convert it to sugars needed to grow. Do you prefer young or old trees? That is the question that scientists continue to debate.

Trees absorb CO2 faster in their youth because they grow faster, but their density increases as they age, allowing them to absorb more CO2. As the tree grows, it can lock away the carbon in its branches, roots, and trunk, playing a pivotal role in combating global warming. Not all trees are equally environmentally friendly.

Even within the same species, the carbon absorption capacity of trees varies greatly. Many factors must be considered, such as the species, age, size, weather conditions, soil type, etc. Amazingly, a tree can purify nearly one million cubic meters of air by growing one cubic meter.

Let’s recall the process of photosynthesis to recall how plants absorb CO2 and release oxygen.

  • Step 1: Plants make sap by absorbing water and minerals through their roots.
  • Step 2: The sap flows from the trunk to the leaves. The leaves absorb CO2 and light.
  • Step 3: The leaves convert CO2 and water into glucose using chlorophyll and the sun’s energy.
  • Step 4: Oxygen is released, and the sap transports glucose to nourish the tree. As it grows, it purifies the air.
  • Note 1: A little-known fact is trees breathe some oxygen at night and release CO2 through respiration.
Plants absorb CO2 for photosynthesis

Plants will absorb less CO2 as the climate warms

Birdlike dinosaurs roamed what was then a lush landscape when the atmosphere contained as much carbon dioxide as it does now. The abundance of CO2, which plants use for photosynthesis, contributed to the Earth’s lushness. As a result, some people believe that increasing CO2 levels in the atmosphere will make the planet greener.

Today, plants and soil worldwide absorb roughly a quarter of the greenhouse gasses that humans release into the atmosphere, helping the Earth avoid some of the worst effects of climate change. In an ideal situation, as carbon dioxide levels increased, plants would soak up more of these emissions, helping to fuel their growth. But plant tissues degrade and are absorbed into the soil as they die.

While this process produces CO2 naturally through the respiration of bacteria that break down dead organisms, some plant carbon can remain underground for decades or even centuries. Plants and soils store about 2,500 gigatonnes of carbon, roughly three times the amount contained in the atmosphere.

Are humans to blame?

Trees are great natural carbon storehouses. Thus it seems to sense that increasing plant abundance over the planet could lower CO2 levels in the atmosphere. However, humans are altering many parts of the natural environment by heating the planet, changing the rainfall pattern, and chopping the large area of the forest into tiny fragments. Much scientific research or debate is going on because of the complicated ways humans affect Earth.

In a study by Nature, researchers found that plants and soil may start drinking less, accelerating the rate of change under a warming climate rather than absorbing more greenhouse gas emissions. Climate scientists are well aware that carbon dioxide concentrations in the atmosphere rise during dry years, indicating that the Earth is absorbing fewer emissions.

Plants are stressed when the soil is dry, and they can’t absorb as much CO2 to perform photosynthesis. At the same time, because dry weather is frequently accompanied by warm temperatures, soil microorganisms, which are more productive when the weather is warm, release more CO2.

As the climate changes, scientists know that there will be more years of extreme weather. That means severe droughts will become more likely, followed by heavier-than-average rainfall years. Scientists are already beginning to see more of these sorts of climactic seesaws. As they occur, the new research suggests that they will reinforce global warming.

Are humans to blame

Plants are losing their ability to absorb carbon dioxide

Plants are significant in climate change mitigation. The more CO2 they absorb during photosynthesis, the less CO2 remains trapped in the atmosphere, potentially raising temperatures. However, scientists have discovered an alarming trend: 86 percent of land ecosystems worldwide are becoming less efficient at absorbing rising CO2 levels from the atmosphere.

Because CO2 is a primary “ingredient” that plants need to grow, elevated concentrations cause an increase in photosynthesis and, consequently, plant growth – a phenomenon aptly referred to as the CO2 fertilization effect (CFE). CFE is a key factor in vegetation’s response to rising CO2 levels in the atmosphere and a key mechanism for removing this potent greenhouse gas from our atmosphere – but that may be changing.

Researchers analyzed multiple fields, satellite-derived and model-based datasets for a new study published in Science better to understand the impact of increasing CO2 levels on CFE. Their findings have significant implications for the role trees play in mitigating climate change in the future.

“We found that the global average CFE has steadily decreased from 21% to 12% per 100 ppm of CO2 in the atmosphere since 1982,” said Ben Poulter, study co-author and scientist at NASA’s Goddard Space Flight Center. “To put it another way, terrestrial ecosystems temporarily lose their ability to mitigate climate change.”

What's Causing It?

Climate change would have happened much faster if there had been no feedback between photosynthesis and increased atmospheric CO2. However, scientists are concerned about how long the CO2 Fertilization Effect can last before other plant growth constraints kick in. For instance, while an abundance of CO2 won’t limit growth, a lack of water, nutrients, or sunlight will be the other necessary components of photosynthesis.

The study team considered the availability of these other elements when determining why the CFE has been decreasing. “According to our data, what appears to be happening is that there’s both a moisture limitation and a nutrient limitation coming into play,” Poulter said. The study team considered the availability of these other elements when determining why the CFE has been decreasing.

Next steps to combat this situation

The international science team found that remote-sensing observations were taken into account – including vegetation index data from NASA’s Advanced Very High-Resolution Radiometer (AVHRR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments – the decline in CFE is more substantial than the current land-surface models have shown. Poulter says this is because modelers have struggled to account for nutrient feedback and soil moisture limitations – due, in part, to a lack of global observations of them. 

The study results also highlight the importance of the role of trees in the global carbon cycle. According to Poulter, as land ecosystems’ carbon-uptake efficiency declines, the amount of CO2 left in the atmosphere may increase as fossil fuel burning and deforestation increase, reducing the remaining carbon budget.

Could planting trees make a significant enough difference to reduce global CO2 levels?

The concept appears simple. Because trees and plants absorb CO2 for photosynthesis, planting enough trees should help to reduce CO2. The biosphere, which includes plants and trees, believe it or not, does impact global CO2 levels.

When combined with oceans, the terrestrial biosphere removes about 45 percent of the CO2 emitted by human activities each year. According to research conducted at UC Berkeley, as global CO2 levels have risen, the terrestrial biosphere has responded by absorbing more CO2 and slowing the rate of global CO2 growth. It’s logical.

According to another research, a typical hardwood tree can absorb up to 48 pounds of carbon dioxide per year. When it reaches 40 years old, it will have sequestered about 1 ton of CO2. A ton of CO2 is a significant amount. However, human activity emits about 40 billion tons of CO2 into the atmosphere each year.

In theory, we’d have to plant 40 billion trees every year and then wait decades to see any positive results. After 40 years, the trees we had planted would have only served to offset the current CO2 levels. Contrary to this statement, National Geographic states, “An area the size of the United States could be restored as forests, with the potential of erasing nearly 100 years of carbon emissions.”

Could Planting Trees Make A Significant Enough Difference To Reduce Global CO2 Levels

Contribution of trees to climate change

Our ecosystem would be incomplete without trees. They are commonly referred to as the “lungs of the Earth” because they are essential in storing CO2 and producing oxygen. Protecting, preserving, and planting trees offers a real opportunity to offset carbon emissions and combat global warming. We must address global warming as soon as possible.

The leading cause is rising greenhouse gas concentrations in the atmosphere. Saving and planting trees is probably the best way to stop it because of their ability to absorb carbon and produce oxygen. According to a Swiss study, we need to plant 1.2 billion trees to absorb two-thirds of the CO2 produced by humans since the Industrial Revolution.

The distinction between air pollution and greenhouse gasses is critical—both of them cause climate change. However, air pollutants (carbon monoxide and nitrogen oxides) harm human health.

Carbon storage in forest soils or processed wood products through photosynthesis, on the other hand, does not usually have a direct impact on health.

When burning, trees release all the carbon dioxide they have absorbed. However, while reforestation aids in the fight against global warming, it is also critical to try to reduce CO2 emissions before reforestation. Any carbon offsetting strategy must be preceded by efforts to reduce your carbon footprint.

It can be accomplished in several ways by making changes in your daily routine, such as:

  • Switching to a green energy provider.
  • Avoid using your vehicle for short journeys and consider using public transport such as buses or trains for longer trips.
  • Reduce the amount of meat you consume.
  • Adopt a more environmentally sustainable lifestyle.
Ben McInerney
Author: Ben McInerney - Ben is a qualified arborist with 15 plus years of industry experience in Arboriculture. He ran a successful tree service before turning to writing and publishing. Ben is dedicated to providing users with the most accurate up-to-date information on everything trees.