1009. Rethinking ‘Net Zero’ for Realizing Climate Targets 

With not only more than 100 countries but also several hundred municipalities and companies committing to reduce their net greenhouse gas emissions by mid-century, ‘net zero’ as a phrase has become a tremendous success. 
An opinion piece published in the journal PNAS in late April noted that while the net zero goal has become a beacon of hope, more comprehensive climate mitigation efforts should be embraced.
 

The concept of net zero is founded on climate science. Earth’s stability depends on the oceans, whose CO₂-absorbing capacity has a cooling effect, while the atmosphere, through the phenomenon of thermal inertia, has continued to have a warming effect for a few decades. 

The concept of net zero became more widely known to the public with the publication of the IPCC report “Global Warming of 1.5°C.”. To limit global warming to 1.5°C, the world should not only cut emissions deeply but also balance ongoing sources of residual emissions by removing a significant amount of CO₂ from the atmosphere. Residual emissions include CO₂ from concrete manufacturing or nitrous oxide from fertilizers, which are difficult to completely eliminate.  　

In reality, the success of net zero depends on whether technologies that remove CO₂ from the atmosphere become feasible. Some estimates indicate that average residual emissions in developing countries will amount to 18% of current total emissions at the time of zero, extrapolated to a global annual removal of at least 12 billion tonnes of CO₂. In turn, natural solutions such as reforestation could offset only a small fraction of such CO₂, while natural ecosystems will become increasingly vulnerable to fire, pests, and diseases in a warming world. Most of the available technologies, which operate on a small scale, are expensive, and face challenges in scaling up, are estimated to collectively remove only about two million tonnes of CO₂ per year. Large-scale deployment of biomass-based CO₂ removal could compete for land with agriculture and/or ecosystems. 

Without setting a target for removals, there would be no clear incentives for each country or company to make efforts to reduce emissions. Instead, they may opt to pay others to remove CO₂ on their behalf. Some scientists call for broader language beyond mere zero emissions, emphasizing the need to conceptualize to encourage people to change their lifestyles and consumption patterns to drive a larger transformation. 

Reference
Stephen Battersby (2024) “Net zero” may need a rethink to keep climate targets within reach
PNAS. April 25, 2024. 121 (18) e2407160121 https://doi.org/10.1073/pnas.2407160121

Contributor: IIYAMA Miyuki (Information Program)