In this course, we’ll be looking at these negative emissions technologies to see how we could remove CO₂ from the atmosphere and at what cost.
How much CO₂ do we need to remove?
Since the industrial revolution in the 1800s, we have emitted about 2400 billion tonnes of CO₂ (GtCO₂) 
. Now, we are emitting around 42 billion tonnes (Gt) of CO₂ every year! If we are going to have a chance at limiting global warming to 1.5°C (as advised by the 2015 Paris Agreement), we can only emit 580 billion more tonnes of CO₂. That sounds like a lot, but at the current rate, we will use this budget up in just 20 years!
To avoid catastrophic warming, we will need to remove some CO₂; the amount we need to remove will depend on how quickly we reduce our emissions now.
If we are very successful at reducing emissions, planting more trees could be enough to absorb the excess CO₂ . If we continue as we are, however, about a trillion tonnes (or 1000 gigatonnes (Gt)) of CO₂ will need to be removed .
So, what solutions will we be looking at? Well, negative emissions technologies can be split into two categories: nature-based solutions and technological solutions.
Nature-based solutions involve working to conserve, restore, and expand the natural ecosystems that absorb CO₂ from the environment (called carbon sinks) . These solutions include:
- Reforestation and afforestation
- Soil carbon sequestration (SCS)
- Biochar
Technological solutions use technology to capture and store CO₂ from the environment and include:
- Enhanced weathering
- Bioenergy with carbon capture and storage (BECCS)
- Direct air capture (DAC)
After this, we will look at whether reflecting solar energy before it is absorbed by the Earth (something called solar radiation management) is a realistic solution for limiting global temperatures.
But before we look at complicated new technologies, let’s look at how nature could help us with our carbon conundrum…
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