To reach “net-zero” emissions we need to not only reduce greenhouse gas emissions, but also to remove CO2 from the atmosphere  (for more on what “net-zero” means, see yesterday’s post). How can we remove CO2?
1) Direct Air Capture: there are a few teams of engineers building machines which “suck” CO2 out of the air [e.g. 8,9]. However, this is currently very expensive, costing over $100 to remove one tonne of CO2 .
2) Bio Energy with Carbon Capture and Storage (BECCS) : this involves growing plants, which naturally take up CO2 from the air as part of photosynthesis, and burning them in a power station to generate electricity . Burning the plants releases the CO2 that they originally took up, but machinery can be used to capture the CO2 again and store it so it doesn’t enter the atmosphere .
3) Restoring natural ecosystems : it has become popular for organisations and governments to plant lots of trees [1,2,3] to take CO2 out of the air . We need to avoid plantations of just one tree species (monocultures) which are vulnerable to climatic extremes, pests and disease, and avoid replacing other natural habitats like grassland which can be more resilient to drought and wildfire .
4) Using soil to take up CO2, by changing farming practices : this can also make crops grow better and improve food security .
We likely need a combination of methods for removing CO2 from the atmosphere . However, to successfully slow climate change we need every country on board . This is a big challenge. For example, Russia was the 4th biggest contributor of global CO2 emissions in 2017  but has weak climate targets; if every country had similar targets to Russia then global warming would exceed 4°C , rather than staying below 1.5°C as governments have agreed to aim for .
 https://ourworldindata.org/co2-and-other-greenhouse-gas-emissions See: Share of global CO2 emissions by country, 2017
 https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_summary-for-policymakers.pdf See: SPM.2 paragraph 5 (“Effective mitigation will not…”)
 https://www.american.edu/sis/centers/carbon-removal/upload/fcea_wps002_ishimoto.pdf See: Cost estimates by technology developers
 https://www.sciencedirect.com/science/article/pii/S030626191730291X#b0010 See: Introduction
 https://www.nature.com/articles/s41558-019-0405-0 See: A focus on forests
 https://www.nature.com/articles/s41558-019-0405-0 See: The problem with monocultures & What about the rest?
 https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_summary-for-policymakers.pdf See: SPM.4 paragraph 4
 https://www.ipcc.ch/sr15/chapter/chapter-4/ See: 4.3.7 Carbon Dioxide Removal (CDR)
 https://www.ipcc.ch/sr15/chapter/chapter-4/ See: 126.96.36.199 Afforestation and reforestation (AR)
 https://www.ipcc.ch/sr15/chapter/chapter-4/ See: 188.8.131.52 Soil carbon sequestration and biochar
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