什么是“直接空气捕集”，它能帮助应对气候变化吗？

Governments and industries increasingly are exploring ways to remove carbon dioxide (CO2) from the atmosphere. CO2 is a major polluter. The waste gas traps heat in the atmosphere, causing the planet to warm.

The United States launched a $3.5 billion program last year aimed at the permanent storage of CO2 using a process known as Direct Air Capture (DAC).

DAC technology uses chemical reactions to remove carbon dioxide from the air. The CO2 can then be stored underground or used in making products such as concrete or aviation fuel.

The world's largest operating DAC plant, Climeworks' Orca plant in Iceland, can remove about 3,600 metric tons of CO2 each year. The CO2 is then stored deep underground.

The US program hopes to build much larger plants that could store almost one million metric tons each year.

Natural ways to remove carbon, such as planting trees and forest management, cost far less than DAC, currently. Data from The World Resources Institute, an environmental and research organization, say these natural methods cost close to $50 per metric ton of carbon, while DAC currently costs closer to $1,000 per metric ton.

Other types of carbon removal

There are still other ways to deal with CO2, like BECCS. The bioenergy with carbon capture and storage process uses the electricity produced by burning biomass such as small wood pieces. The CO2 is captured and stored during its release.

Biochar is a form of charcoal produced when organic matter such as leaves and wood is heated at high temperatures without oxygen. This produces a carbon rich substance that can be used as fertilizer.

Techniques are also being developed to remove CO2 from seawater.

Carbon capture and storage (CCS) is another technology to deal with CO2.

CCS is traditionally deployed at industrial smokestacks such as fossil fuel power factories. It captures the CO2 and stores it before it reaches the atmosphere.

CCS is considered carbon removal only if it stores more carbon than the site releases.

Carbon removal methods such as DAC may be very useful if they can pull pollution from the air and store it permanently in the Earth or in new products.

Some environmental groups worry that companies will use technical solutions like DAC as an excuse not to reduce their CO2 releases. The groups also link the issue to environmental justice as heavy polluting sites are often in, or near, poor and minority communities.

I'm Andrew Smith.

Andrew Smith adapted this story for VOA Learning English based on reporting by Susana Twidale for Reuters.

_________________________________________________________________

smokestack-n. a tall chimney that carries smoke and other gases away from a factory

fossil fuel -n. carbon or hydrocarbon-based fuels such as oil or natural gas, found underground, that come from organic material, such as the remains of plants or animals