- What is Climate Engineering? The different strategies proposed to slow or halt global warming by direct intervention.
- How does Negative Emissions Technology work? Tree Planting, Rock Weathering, Ocean Nutrition, Direct Air Capture, and Biomass with Carbon Capture – the pros and cons of sucking CO2 from the air.
- Could Negative Emissions Technology solve climate change? Why Negative Emissions Technology is useful for slowing Global Warming and offsetting hard-to-abate emissions, but will likely be limited to 10-30% of the solution.
Climate engineering refers to several proposed strategies which are designed to either slow, or prevent, climate change by either directly removing CO2 from the atmosphere (negative emissions technology) or by limiting the amount of solar energy absorbed by the planet (solar radiation management). In this post we are going to dig into the main options for Negative Emissions Technology.
Sucking CO2 from the Atmosphere
Negative Emissions Technology (NET) is designed to draw CO2 back out of the atmosphere in order to reduce radiative forcing (the net-energy inflows into Earth caused by the increases to greenhouse gasses in the atmosphere), and to keep temperature rises at bay.
Here are the techniques which have been proposed to suck CO2 from the air.
- Reducing Deforestation, Reforestation or Afforestation requires stopping the destruction of forests, restoring past forests, or growing new ones and speeding up the land based biological carbon cycle. Trees absorb carbon dioxide using photosynthesis through the day and expel just half as much CO2 through respiration overnight when growing. The average tree draws half a tonne of CO2 from the atmosphere as it grows over 25-75 years and locks it away in the trunk, branches, and root systems. There are already 3 trillion trees on Earth covering 42 million square km or 28% of all dry land.
- Reducing Deforestation: Every year the world loses around 80,000 square km of forest from unsustainable logging and clearing for agricultural land. That’s a land area the size of Austria and, with 50,000 tonnes of CO2 bound up in each square kilometre of forest, this releases four billion tonnes of CO2 emissions from the burning and rotting wood. End deforestation and you eliminate nearly 10% of all CO2e emissions. The cost is estimated at less than $5 per tonne of CO2 to compensate farmers for lost income on potential agricultural land and to ensure the policy is enforced.
- Tree Planting: Scientists estimate there is enough space on the planet to add up to another nine million square kilometres of forest or 0.7 trillion trees without impacting agricultural output.15 This is an area bigger than the United States. This could remove more than 400 billion tonnes of CO2 over the next 50-100 years at a rate of up to 7-8 billion tonnes per year. It costs between $0.5 and $6 to plant and establish one tree depending on the land,16 a total cost of about $2 trillion to plant all potential land.vi Reforestation could work out at less than $10 per tonne of CO2 removed or an added cost of $0.5c per kWh to offset the emissions from fossil fuel energy.
Since the 1990s, China has planted nearly one million square kilometres of new forest, covering 0.7% of all the world’s dryland at a cost of over $100 billion ($3 per tree). Scaling this up to every country in the world, full forest potential could be reached over the coming decades. Tree planting is relatively cheap, effective, and low risk. It also comes with added co-benefits of soil preservation, flood control, and water retention. But it only covers a maximum of 15% of current annual emissions and eventually this strategy runs out of land unless the wood can be sustainably harvested and stored or used. Planting trees is effective, cheap, and low risk, but it can only offset a fraction of emissions.
