Net-zero emissions

Global net-zero emissions is reached when greenhouse gas emissions and removals due to human activities are in balance. Net-zero emissions is often shortened to net zero. Once global net zero is achieved, further global warming is expected to stop.

Emissions can refer to all greenhouse gases or only to carbon dioxide (CO₂). Reaching net zero is necessary to stop further global warming. It requires deep cuts in emissions, for example by shifting from fossil fuels to sustainable energy, improving energy efficiency and halting deforestation. A small remaining fraction of emissions can then be offset using carbon dioxide removal.

People often use the terms net-zero emissions, carbon neutrality, and climate neutrality with the same meaning. However, in some cases, these terms have different meanings. For example, some standards for carbon neutral certification allow a lot of carbon offsetting. But net zero standards require reducing emissions to more than 90% and then only offsetting the remaining 10% or less to fall in line with 1.5 °C targets. Organizations often offset their residual emissions by buying carbon credits.

In the early 2020s net zero became the main framework for climate action. Many countries and organizations are setting net zero targets. As of November 2023, around 145 countries had announced or are considering net zero targets, covering close to 90% of global emissions. They include some countries that were resistant to climate action in previous decades. Country-level net zero targets now cover 92% of global GDP, 88% of emissions, and 89% of the world population. 65% of the largest 2,000 publicly traded companies by annual revenue have net zero targets. Among Fortune 500 companies, the percentage is 63%. Company targets can result from both voluntary action and government regulation.

Net zero claims vary enormously in how credible they are, but most have low credibility despite the increasing number of commitments and targets. While 61% of global carbon dioxide emissions are covered by some sort of net zero target, credible targets cover only 7% of emissions. This low credibility reflects a lack of binding regulation. It is also due to the need for continued innovation and investment to make decarbonization possible.

To date, 27 countries have enacted domestic net zero legislation. These are laws that contain net zero targets or equivalent. There is currently no national regulation in place that legally requires companies based in that country to achieve net zero. However several countries, for example Switzerland, are developing such legislation.

The idea of net-zero came out of research in the late 2000s into how the atmosphere, oceans and carbon cycle were reacting to CO₂ emissions. This research found that global warming will only stop if CO₂ emissions are reduced to net zero. Net-zero was basic to the goals of the Paris Agreement. This stated that the world must "achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century". The term "net zero" gained popularity after the Intergovernmental Panel on Climate Change published its Special Report on Global Warming of 1.5 °C (SR15) in October of 2018, this report stated that "Reaching and sustaining net zero global anthropogenic [human-caused] CO₂ emissions and declining net non-CO₂ radiative forcing would halt anthropogenic global warming on multi-decadal timescales (high confidence)." An influential and now highly-cited scientific review on "Net-zero emissions energy systems" was also published in June of 2018, which was the first to assess the special challenges of not just reducing energy-related GHG emissions but actually reaching net-zero.

The idea of net-zero emissions is often confused with "stabilization of greenhouse gas concentrations in the atmosphere", a term from the 1992 Rio Convention. The two concepts are not the same. This is because the carbon cycle continuously sequesters or absorbs a small portion of human-caused atmospheric CO₂ into vegetation and the ocean, even after CO₂ emissions are reduced to zero. If CO₂ emissions from human activities are reduced to net zero, the concentration of CO₂ in the atmosphere would decline. This would be at a rate just fast enough to compensate for the slow warming of the deep ocean. The result would be approximately constant global average surface temperatures over decades or centuries. In contrast, stabilising atmospheric CO₂ concentrations would allow for some ongoing emissions, but global temperatures would continue to rise over many centuries due to the ocean's delayed response to warming.