6. How can net zero CO2 emissions be reached?

Because collective climate action has been delayed until the Paris Agreement was adopted, much more stringent and expensive options are required to hold global average temperature below 2ºC.  


The IPCC concluded that the full implementation of GHG emission reduction measures by all countries in all sectors will not be enough to hold global average temperature below 2ºC. Thus, additional measures will be required to cut CO2 emissions to net zero, using technologies to reduce CO2 emissions and to remove CO2 from the atmosphere. The reason to focus on CO2 is that it accounts for 65 percent (or about 35 GtCO2) of global GHG emissions as a result of the burning of fossil fuels[1].


One technology to reduce CO2 emissions is carbon capture and storage (CCS). These large-scale industrial plants capture CO2 (from carbon-fueled power plants, refineries, cement plants and steel mills) and store it before it reaches the atmosphere by injecting it deep underground. These CCS plants are expensive, have not been tested at large-scale, and potentially pose risks, such as leakage of CO2 to water, soil or back into the atmosphere. Thus, accelerated research into their financial and environmental viability is needed. Currently, about a dozen CCS plants in the world capture less than 0.1 percent of CO2 emissions (or about 0.036 GtCO2)[2].


One technology that could produce energy and remove CO2 from the atmosphere is the production of bioenergy combined with CCS. The production of energy by burning biomass (such as fuelwood and agricultural residues) coupled with CCS could offer negative emissions because the CO2 absorbed by trees and plants during their growth can be captured and stored deep underground. There are risks and challenges associated with these technologies, also known as negative emission technologies, such as competition for food, land and water to grow the necessary biomass to produce bioenergy sustainably, which could negatively impact livelihoods. Other risks are simply not known, because there are currently no large-scale bioenergy with CCS plants in the world[3].


The inadequate INDCs have accelerated the need to depend on these technologies. To meet the 2ºC target, global CO2 emissions should be net zero by 2060-2075[4].


To cut CO2 emissions to net zero requires not only drastically reducing emissions but also increasing the removal of CO2. Currently, the oceans, trees and plants (or carbon sinks) remove about half of anthropogenic (or man-made) CO2 emissions[5]. Extensive reforestation and conversion of land into forest (afforestation) activities could considerably increase the removal of CO2. But the planting of new forests will not be enough to cut CO2 emissions to net zero because it would imply expanding the current world’s forest cover, at least, twofold. Such massive expansion, though, is constrained by available land. Thus, the large-scale utilization of negative emission technologies will be required. However, the dependence on these negative emission technologies as an option to control climate change is unproven[6]. Even if new negative emission technologies are developed to remove CO2 from the atmosphere, their impact in controlling climate change will not be immediate –global temperature will continue to increase for decades, after these negative emission technologies are applied[7].


The high risks and costs of further postponing decisive climate action, such as the dependence on unproven negative emission technologies, can be reduced by raising the ambition of the INDCs.  Taking earlier action will increase the options of feasible and more cost-effective measures to reduce global GHG emissions[8], and most importantly, will outweigh the risks and damage costs arising from the changing climate[9].





[1] IPCC, AR5, WG III, Chapter 1 (2014)

[2] IPCC, AR5, WG III, Chapter 1 (2014)

[3] IPCC, AR5, WGIII, Chapter 6 (2014)

[4] UNEP The Emissions Gap Report 2015 (2015)

[5] IPCC, AR5, WG I, Chapter 6 (2013)

[6] Betting on Negative Emissions, Nature Climate Change (2014) and UNEP The Emissions Gap Report 2015 (2015)

[7] IPCC, AR5, WG I, Chapter 6 (2013)

[8] UNEP The Emissions Gap Report 2015 (2015)

[9] The Economics of Climate Change, The Stern Review (2006)