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.
As 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 limit. We have to dramatically reduce our carbon dioxide emissions while planting more trees.
- 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 on ncsu.edu (NC State University)
- 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