Limiting global warming to below 2°C above compared to preindustrial times requires not only massive near-term greenhouse gas emissions reductions but also the application of “negative emission” techniques that extract already emitted carbon dioxide from the atmosphere called
The study, published under the title of “The limits to global-warming mitigation by terrestrial carbon removal”, shows that
- Biomass plantations with subsequent carbon immobilization are likely unable to “repair” insufficient emission reduction policies without compromising food production and biosphere functioning due to its space-consuming properties.
- The requirements for a strong mitigation scenario staying below the 2°C target would require a combination of high irrigation water input and the development of highly effective carbon process chains.
Although the study concludes that this strategy of sequestering carbon (planting trees, everywhere) is not a viable alternative to aggressive emission reductions, the researchers say it could still support mitigation efforts if sustainably managed.
Only planting trees is not enough
But we should still plant trees, of course.
Here are some numbers:
- We emit around 36 billion tons of Co2 into Earth’s atmosphere every year.
- A tree can absorb as much as 48 pounds (around 20 kg) of carbon dioxide per year.
- So, we need 1,8 trillion trees to absorb all carbon dioxide we emit into the atmosphere.
- 10 meters is the optimal spacing between two trees.
- We need 180 million km2 land area to plant these trees.
- The problem is, the Earth’s land area is about 149 million km2. So, planting that much of trees is practically impossible.
In a summary, the amount of carbon dioxide in the Earth’s atmosphere has become so large that “only” planting more trees can no longer save us. Because there is not enough space on Earth to plant enough trees to stay within the 2°C warming limit. We have to dramatically reduce our carbon dioxide emissions while planting more trees. Many future climate scenarios suggest that negative emissions (sucking carbon dioxide out of the atmosphere) will be needed to limit global warming.
Humans emit roughly 30 to 40 billion tons of greenhouse gas, carbon dioxide, into the atmosphere each year. If we keep it up, Earth will continue to heat up and ultimately devastate our way of life. So what can we do about it? Most scientists agree that we need a way to capture some of that CO2 out of the atmosphere.
One idea is to plant lots of trees. Trees use CO2 in order to grow. They also release oxygen, so it’s a win-win.
But recent reports indicate that we simply can’t grow enough trees to capture the necessary amount of CO2 that would help us meet the goals set by the Paris Agreement. In truth, the United States, for example, would have to cover the entire area with trees just to capture 10% of the CO2 the US emits annually.
There’s just not enough room on this planet to have the farmland it takes to feed the world plus the space to plant the necessary number of trees. In other words, many of us would starve if we tried using trees to solve our emissions problem.
- How Big is Earth? on Space.com
- Can Sucking CO2 Out of the Atmosphere Really Work? on Technology Review
- Mapping tree density at a global scale on Nature.com
- Tree Facts
- Frequently Asked Global Change Questions on ornl.gov
- “Planting trees cannot replace cutting carbon dioxide emissions, study shows” on blogs.agu.org
- Original study: “The limits to global-warming mitigation by terrestrial carbon removal” by Lena R. Boysen, Wolfgang Lucht, Dieter Gerten, Vera Heck, Timothy M. Lenton, Hans Joachim Schellnhuber. onlinelibrary.wiley.com
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