Net zero emissions
Global net zero emissions describes the state where emissions of carbon dioxide due to human activities and removals of these gases are in balance over a given period. It is often called simply net zero.[2] In some cases, emissions refers to emissions of all greenhouse gases, and in others it refers only to emissions of carbon dioxide (CO2).[2] To reach net zero targets requires actions to reduce emissions. One example would be by shifting from fossil fuel energy to sustainable energy sources. Organizations often offset their residual emissions by buying carbon credits.
People often use the terms net zero emissions, carbon neutrality, and climate neutrality with the same meaning.[3][4][5][6]: 22–24 However in some cases, these terms have different meanings from each other.[3] 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.[7]
In the last few years, net zero has become the main framework for climate action. Many countries and organizations are setting net zero targets.[8][9] As of November 2023, around 145 countries had announced or are considering net zero targets, covering close to 90% of global emissions.[10] They include some countries that were resistant to climate action in previous decades.[11][9] Country-level net zero targets now cover 92% of global GDP, 88% of emissions and 89% of the world population.[9] 65% of the largest 2,000 publicly traded companies by annual revenue[9] have net zero targets. Among Fortune 500 companies the percentage is 63%.[12][13] 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.[14] 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.[15]
To date, 27 countries have enacted domestic net zero legislation. These are laws that legislatures have passed which contain net zero targets or equivalent.[16] There is currently no national regulation in place that legally requires companies based in that country to achieve net zero. Several countries, for example Switzerland, are developing such legislation.[17]
History and scientific justification[edit]
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.[18] 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 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)."[19]
The idea of net zero emissions is often confused with "stabilization of greenhouse gas concentrations in the atmosphere". This is a term that dates from the 1992 Rio Convention. The two concepts are not the same. This is because the carbon cycle continuously sequesters or absorbs a small percentage of cumulative historical human-caused CO2 emissions into vegetation and the ocean. This happens even after current CO2 emissions are reduced to zero.[20] If the concentration of CO2 in the atmosphere were kept constant, some CO2 emissions could continue. However global average surface temperatures would continue to increase for many centuries due to the gradual adjustment of deep ocean temperatures. If CO2 emissions that result directly 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 this deep ocean adjustment. The result would be approximately constant global average surface temperatures over decades or centuries.[21][20]
It will be quicker to reach net-zero emissions for CO2 alone rather than CO2 plus other greenhouse gases like methane, nitrous oxide and fluorinated gases.[22] The net-zero target date for non-CO2 emissions is later partly because modellers assume that some of these emissions such as methane from farming are harder to phase out.[22] Emissions of short-lived gases such as methane do not accumulate in the climate system in the same way that CO2 does. Therefore there is no need to reduce them to zero to halt global warming. This is because reductions in emissions of short-lived gases cause an immediate decline in the resulting radiative forcing. Radiative forcing is the change in the Earth's energy balance that they cause.[23] However, these potent but short-lived gases will drive temperatures higher in the short term. This could possibly push the rise in temperature past the 1.5 °C threshold much earlier.[22] A comprehensive net-zero emissions target would include all greenhouse gases. This would ensure that the world would also urgently reduce non-CO2 gases.[22]
Terminology[edit]
Countries, local governments, corporations, and financial institutions may all announce pledges for achieving to reach net zero emissions.[24]
In climate change discussions, the terms net zero, carbon neutrality, and climate neutrality are often used as if they mean the same thing.[3][4][5][6]: 22–24 In some contexts, however, they have different meanings from each other. The sections below explain this.[3] People often use these terms without rigorous standard definitions.[25][3]
Standards for products[edit]
Leading standards and guidance allow official accreditation bodies to certify products as carbon neutral but not as net zero.[29] The rationale behind this is that until organizations and their supply chains are on track for net zero, allowing a product to claim to be net zero at this point would be disingenuous and lead to greenwashing.[29]