1.2 Fastest

The next aspect you might consider is the speed at which the method acts. If you were under pressure from politicians to counteract climate change, might you choose the fastest technique?

Solar Radiation Management methods would generally be faster at changing Earth’s energy balance than Carbon Dioxide Removal methods. This is because SRM methods work through either:

• direct reflection of solar radiation, and/or
• processes on timescales that range from hours (e.g. cloud formation) to months (e.g. distribution of aerosols around the stratosphere).

In contrast, CDR methods are inherently slow due to:

• the limited speed of the processes (e.g. photosynthesis, chemical extraction, CCS, ocean circulation, tree growth)
• their limited scale (e.g. amount of land used or ocean fertilised, size of geological reservoir), and
• the various ways in which CO₂ can re-enter the atmosphere (e.g. leaks from reservoirs and the ocean, non-carbon-neutral energy used).

This means it will take decades to extract and sequester substantial amounts. If CO₂ emissions continue increasing, this makes the task even slower.