Removing carbon from atmosphere

Keeping global warming below 2°C

Expanding forests, restoring existing forests and managing forests can help remove carbon dioxide from the atmosphere.

Since the Industrial Revolution, humans have emitted more than 2,000 gigatonnes of carbon dioxide into the atmosphere. (A gigatonne is one billion tonnes.)

If nothing changes, climate impacts such as forest fires, stifling heat waves and damaging sea level rise will only continue to intensify. The imperative for combatting climate change is to dramatically curb emissions—for example, by ramping up renewable energy, boosting energy efficiency, halting deforestation and curbing super pollutants like hydrofluorocarbons (HFCs).

To keep global temperature rise to less than 1.5-2 degrees C, some scientists believe that we need to not only reduce emissions, but also to remove some carbon from the atmosphere estimated at billions of tonnes of carbon dioxide annually by mid-century.

Graphics of carbon removal

Here are six options for removing carbon from the atmosphere:

1.       Forests

Photosynthesis removes carbon dioxide naturally—and trees are especially good at storing carbon removed from the atmosphere by photosynthesis. Expanding forests, restoring existing forests and managing forests will store carbon in wood and soils.

However, reforesting farmland would reduce the supply of food. Restoring land outside of farmland and managing existing forests are important.

2.       Farms

Soils naturally store carbon, but agricultural soils are running a big deficit due to intensive use. Building soil carbon is good for farmers and ranchers, as it can increase soil health and crop yields. Integrating trees on farms can also remove carbon while providing other benefits like shade and forage for livestock.

There are many ways to increase carbon in soils - planting cover crops, sequestering about half a metric tonne of CO2per acre per year and compost making

3.       Bio-energy with Carbon Capture and Storage (BECCS)

BECCS is another way to use photosynthesis to combat climate change. It is the process of using biomass for energy in the industrial, power or transportation sectors; capturing the embodied carbon before it is released back to the atmosphere; and then storing it either underground or in long-lived products like concrete.

If BECCS relies on bioenergy crops, it could displace food production or natural ecosystems, erasing the apparent climate benefits and exacerbating food insecurity and ecosystem loss.

4.        Direct Air Capture

Direct air capture is the process of chemically scrubbing carbon dioxide directly from the ambient air, and then storing it either underground or in long-lived products. The technology remains costly and energy-intensive. One estimate is that it would cost about $94-$232 per tonne.

Direct air capture also requires substantial power inputs. The technology need further development and would need to be powered by low- or zero-carbon energy sources to result in net carbon removal.

5.       Seawater Capture

Seawater capture is akin to direct air capture, except CO2 is extracted from seawater instead of air. By reducing CO2 concentration in the ocean, the water then draws in more carbon from the air to regain balance. Seawater capture will have to grapple with the added complexities of technology deployment in harsh maritime environments.

6.       Enhanced Weathering

Some minerals naturally react with CO2, turning carbon from a gas into a solid. The process is commonly referred to as “weathering,” and it typically happens very slowly—on a geological timescale. But scientists are figuring out how to speed up the process, especially by enhancing the exposure of these minerals to CO2 in the air or ocean.

The Future of Carbon Removal

We don’t know today which of these strategies can provide the most large-scale carbon removal in the future, and which may ultimately prove less useful. Each approach offers both promise and challenges. (WRI)