A new research paper by Professor Myles Allen and colleagues in Annual Review of Environment and Resources explains the science behind the drive for global net zero emissions and why this is needed to halt the ongoing rise in global temperatures. The paper presents the science behind net zero in a form accessible to students, using a simple climate model to demonstrate key concepts.
It defines the term net zero emissions as a balance between ongoing anthropogenic (human-caused) release of greenhouse gases into the atmosphere, and active Greenhouse Gas Removal. It can be applied to an individual gas, such as CO₂, or a basket of gases.
The paper explains why we need net zero emissions of CO₂, to halt the rise in global temperatures, and how this understanding emerged from a pre-2009 emphasis on stabilisation of atmospheric concentrations of CO₂.
Some of the article’s key points include:
- Durable, climate-neutral net zero strategies require like-for-like balancing of anthropogenic greenhouse gas sources and sinks in terms of both origin (biogenic versus geological) and gas lifetime.
- Since the concept of net zero was taken up through the 5th Assessment Report of the IPCC and UNFCCC Structured Expert Dialogue, culminating in Article 4 of the Paris Agreement, increasing numbers of net zero targets have since been adopted around the world, by countries, cities, corporations and investors. The sustainability of a net zero strategy as a whole, and its implications for global temperature over multidecadal time scales, is crucial.
- CO₂ emissions have a substantial and effectively permanent impact on global climate, which is why sustained net zero CO₂ emissions are needed to restore climate equilibrium, on multimillennial timescales. Approximately net zero CO₂ emissions are also required on multidecadal timescales to stop global warming, through a balance between CO₂ uptake by oceans and the biosphere and the ongoing thermal adjustment of the deep oceans and evolving atmospheric feedbacks.
- Nature-based solutions (NbS) provide immediate cost-effective opportunities for reducing net CO₂ emissions with substantial co-benefits, but they will likely be needed in the future to compensate for essential emissions (e.g. from food production) and the release of carbon from the biosphere due to global warming itself. NbS are unlikely to be scaled sufficiently to compensate for ongoing fossil fuel emissions past mid-century.
The authors of the paper are: Myles R. Allen, Pierre Friedlingstein, Cécile A.J. Girardin, Stuart Jenkins, Yadvinder Malhi, Eli Mitchell-Larson, Glen P. Peters, and Lavanya Rajamani. Four of the authors, Myles R. Allen, Stuart Jenkins, Eli Mitchell-Larson and Lavanya Rajamani are part of Oxford Net Zero.
Read the report (PDF).