Net zero emissions

Global net zero is a state in which human-caused greenhouse gas emissions are balanced by human-caused greenhouse gas removals over a specified time period. When used in shorthand, net zero generally refers to the IPCC SR1.5 pathway for a 50% chance at limiting warming to 1.5 °C with no or limited overshoot, meaning approximately halving emissions by 2030 vs current levels and reaching global net zero by 2050.

In the last few years, net zero has become the dominant framework for climate ambition with countries and organizations alike setting net zero targets. Today more than 140 countries have a net zero emissions target, including some countries which were resistant to climate action in previous decades. Country-level net zero targets now cover 92% of the global GDP, 88% of emissions and 89% of the world population. At a company level, 65% of the largest 2,000 publicly traded companies by annual revenue and 63% of Fortune 500 companies have net zero targets. Company targets are a result of voluntary action as well as government regulation.

Despite an increasing prevalence of commitments and targets, however, net zero claims vary enormously in levels of credibility and most have low credibility. While 61% of global carbon dioxide emissions are covered by some sort of net zero target, credible targets cover only 7% of emissions. Low credibility in targets reflects a lack of binding regulation and the need for continued innovation and investment to permit decarbonization.

To date, 27 countries have enacted domestic net zero legislation – laws passed by the legislative branch of government that contain net zero targets or equivalent. While there is currently no national regulation in place that legally mandates companies based in that country achieve net zero, legislation is being developed in several countries, most notably Switzerland.

History and scientific justification

The concept of net zero has its roots in research into the response of the atmosphere, oceans and carbon cycle to CO₂ emissions in the late 2000s, which found global warming will only stop if CO₂ emissions are reduced to net zero. Net zero was integral to the goals of the Paris Agreement, which asserted we must "achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century". The specific term "net zero" gained popularity after the Intergovernmental Panel on Climate Change published a Special Report on a Global Warming of 1.5 °C (SR1.5) stating that "[i]n model pathways with no or limited overshoot of 1.5 °C, global net anthropogenic CO₂ emissions decline by about 45% from 2010 levels by 2030, reaching net zero around 2050."

The scientific justification of net zero is summarised earlier in the Summary for Policymakers of SR1.5, thus: "Reaching and sustaining net zero global anthropogenic CO₂ emissions and declining net non-CO₂ radiative forcing would halt anthropogenic global warming on multi-decadal timescales (high confidence)." The context of this sentence is that the anthropogenic (human-induced) change in global average surface temperature $\Delta T$ over a multi-decade time-period $\Delta t$ is given, to a good approximation, by $$\Delta T=\kappa _{E}[E_{\rm {GEO}}+E_{\rm {LUC}}+(\rho _{F}-\rho _{E})C_{E}]\Delta t+\kappa _{F}(\Delta F+\rho _{F}F\Delta t)$$where the first term indicates CO₂-induced warming and the second term indicates warming due to the net impact of other anthropogenic drivers such as emissions of methane, nitrous oxide or aerosol precursors.

Of the variables in this equation, $E_{\rm {GEO}}$ is the average rate of CO₂ emissions over this time-period from geological sources (such as fossil fuel combustion and cement production, minus any engineered CO₂ removed to geological storage). $E_{\rm {LUC}}$ is the corresponding average rate of CO₂ emissions from land-use change, agriculture and forestry minus CO₂ removed by active interventions such as afforestation and nature-based solutions: it does not include CO₂ uptake by the biosphere that occurs as a result of past CO₂ emissions due to natural processes such as CO₂ fertilisation. $C_{E}$ is cumulative CO₂ emissions since pre-industrial times up to the middle of this time-period. $\Delta F$ is the change in net non-CO₂ radiative forcing over this time-period (shorter timescale adjustments can be accounted for by taking $\Delta F$ as the difference between the decade prior to the beginning and decade prior to the end of the time-period) and $F$ is the average non-CO₂ radiative forcing over this time-period.

Approximately constant coefficients include $\kappa _{E}$, the Transient Climate Response to Emissions, about 0.45 °C per TtCO₂ (trillion tonnes of CO₂); $\kappa _{F}$ is the Transient Climate Response to Forcing, about 0.49 Watts per m² per TtCO₂; $\rho _{F}$ is the fractional Rate of Adjustment to Constant Forcing, or the fractional rate at which global average surface temperature would continue to increase over the decades following a forcing stabilisation, which is about 0.3% per year; and $\rho _{E}$ is the fractional Rate of Forcing Decline under Zero CO₂ Emissions, also about 0.3% per year.

The fact that $\rho _{F}\simeq \rho _{E}$ means that the third term in the square brackets is approximately zero, and hence that net zero CO₂ emissions, $E_{\rm {GEO}}+E_{\rm {LUC}}=0$, and declining net non-CO₂ radiative forcing, $\Delta F/\Delta t\simeq -\rho _{F}F$, is sufficient to halt global warming, $\Delta T=0$, justifying the SR1.5 statement. Despite this cancellation, the term $\rho _{E}C_{E}$ represents an important process. It is the "passive" uptake of CO₂ by the biosphere and oceans that would continue for decades even if all human activity were to cease (called passive because it requires no active human intervention, although it might require very active protection of natural carbon sinks).

Implementation

Countries, local governments, corporations, and financial institutions may announce pledges for achieving net zero emissions for themselves; these entities are known as actors. Since 2015, there has been significant growth in the number of actors pledging net zero emissions. A plethora of standards have arisen that interpret the net zero concept and aim to measure progress towards net zero targets. Some of these standards are more robust than others, and weak standards have been criticized for facilitating greenwashing. More robust standards are promoted by the UN, UNFCCC, ISO, and SBTi

Types of greenhouse gas

Some targets aim to reach net zero emissions only for carbon dioxide, whereas others aim to reach net zero emissions of all greenhouse gases. Robust net zero standards state that all greenhouse gases should be covered by a given actor's targets.

Emission reductions, carbon removals, and offsetting

A given actor may plan to achieve net zero emissions through a combination of: 1) actions to reduce their own emissions, 2) actions to directly remove carbon dioxide from the atmosphere, and 3) purchasing carbon credits.

Emission reductions

According to robust net zero standards, actors must reduce their own emissions as much as possible following science-based pathways and then balance their residual emissions using removals and offsets. Residual emissions are those which cannot be feasibly reduced due to either technological constraints.

Experts and net zero frameworks disagree over the exact percentage of residual emissions that may be allowable, but most guidance suggests this should be limited to a small fraction of total emissions determined by sector-specific and geographical factors. SBTi directs residual emissions across most sectors should fall between 5-10% of an organization's baseline emissions, and even lower for some sectors with competitive alternatives like the power sector. Hard-to-abate sectors, such as heavy manufacturing, will likely have a higher percentage of residual emissions by 2050.

Carbon removals and offsets

To balance residual emissions, actors may take direct action to remove carbon dioxide from the atmosphere and sequester it, and/or they can buy carbon credits that "offset" emissions. Carbon credits can be used to fund carbon removal projects such as reforestation. They can also fund initiatives that aim to avoid emissions, such as energy efficiency retrofits or renewable energy projects. Avoided emissions offsets are those resulting from actions which reduce emissions relative to a baseline or status quo, but do not remove emissions from the atmosphere.

Weak standards, such as ISO and BSI's "carbon neutrality" standards, allow organizations to use avoided-emissions carbon credits and do not specify how permanent or durable a credit must be. Stronger standards such as the ISO and BSI "net zero" standards only allow removal-based offsets that are equal in permanence as the greenhouse gases that they balance. Permanence means that removals must have equally long-term storage relative to the lifetime the GHG emissions they balance. For example, methane has a lifetime of around 12 years in the atmosphere whereas carbon dioxide lasts between 300 - 1,000 years. Accordingly, removals that balance carbon dioxide must last much longer than removals that balance methane.

Most of the carbon credits on the voluntary market today do not meet UN's, UNFCCC's, ISO's or SBTi's standards for permanent carbon dioxide removals. Accordingly, significant investment in carbon capture and permanent geological storage will likely be required to achieve net-zero targets by mid-century.

Timeframe

To achieve net zero, actors are encouraged to set net zero targets for 2050 or earlier. Long-term net zero targets should be supplemented by interim targets for every one to five years. The UN, UNFCCC, ISO, and SBTi all assert that organizations should prioritize early, front-loaded emissions reduction and should aim to halve emissions by 2030. Specific emissions reduction targets and pathways may look different for different sectors, with some able to decarbonize more quickly and easily than others.

Comprehensive accounting

Actors are encouraged to include emissions across their full value chain (scope 1, scope 2 and scope 3 emissions) and CO₂ and other greenhouse gas emissions within the scope of their net zero targets. Per leading guidance, organizations should choose a base year to measure emissions reductions against, which is representative of their "typical GHG profile", and they should disclose "why the baseline has been chosen and how changes in conditions since the baseline will be accounted for". Financial organizations should also include the emissions within their portfolio, including all organizations they have financed, invested in, or insured. Countries and regions should include territorial emissions (emissions released within its boundaries) and consumption emissions (GHG emissions related to products and services consumed within its boundaries).

Equity and impact

The concept of net zero has been the subject of some criticism over its potentially negative equity and distributional effects. In particular, the use of removals or carbon credits for offsetting has been controversial due to the perception offset projects themselves could have harmful effects. A report by Friends of the Earth asserts REDD+ carbon removal offsets "lead to or promote a variety of devastating impacts, including land grabs, forced displacement, militarization, and loss of livelihoods and biodiversity". Considering these potential negative effects, the ISO Net Zero Guidelines assert net zero strategies should align with the United Nations Sustainable Development Goals to "support equity and global transition to a net zero economy, and any subsequent UN global goals which supersede the 2030 SDGs." Moreover, the UNFCCC's Race to Zero campaign asserts emissions reductions and removals should "safeguard the rights of the most vulnerable people and communities", and organizations should disclose how they will support communities affected by climate impacts and climate transition.

Credibility

Status of countries' net zero targets, as of Nov 2021. The inclusion criteria for net zero commitments may vary from country to country.

Despite an increasing prevalence of both nations and organizations (private and public sector) committing to net zero, the credibility of these claims remains low. Given the lack of any binding regulation mandating a transition to net zero, the overwhelming majority of net zero commitments have been made on a voluntary basis. The lack of an enforcement mechanism surrounding these claims means that many are dubious. In addition, in many sectors such as steel, cement, and chemical production, the pathway to achieving net zero remains technologically unclear. Further investment in research and innovation, as well as further regulation, will likely be necessary if net zero claims are to increase in credibility.

The role of carbon credits

A primary reason for the low credibility of many net zero claims is the heavy reliance on carbon credits. Carbon credits are often used for offsetting, and are a reduction or removal of emissions of carbon dioxide or other greenhouse gases made in order to compensate for emissions made elsewhere. For example, many fossil fuel companies have made pledges to be net zero by 2050, while their extraction practices continue to increase greenhouse gas emissions. These claims are based on the fossil fuel companies assertions that they will use carbon credits and carbon capture technology in order to continue extracting and burning fossil fuels, and have been condemned by the UN as dangerous examples of greenwashing.

Criticism

Tracing the history of certain illusions in climate policy from 1988 to 2021, climate scientists James Dyke, Robert Watson, and Wolfgang Knorr "[arrive] at the painful realisation that the idea of net zero has licensed a recklessly cavalier 'burn now, pay later' approach which has seen carbon emissions continue to soar... Current net zero policies will not keep warming to within 1.5 °C because they were never intended to. They were and still are driven by a need to protect business as usual, not the climate. If we want to keep people safe then large and sustained cuts to carbon emissions need to happen now. ...The time for wishful thinking is over."

In March 2021, Tzeporah Berman, chair of the Fossil Fuel Non-Proliferation Treaty Initiative, argued that the Treaty would be a more genuine and realistic way to achieve the goals of the Paris Agreement than the "Net zero" approach which, she claimed, is "delusional and based on bad science".

Eric Reguly, of The Globe and Mail states that, "The net-zero pledges are both welcome and dubious. Most are back-end loaded, meaning the majority of the cuts are to come well after 2030... Most of these targets also assume...steady technological advances and outright breakthroughs...Fossil fuel exports will not figure into the national accounting for the net-zero goal."

In his 16-page report, Dangerous Distractions, economist Marc Lee states that, "'Net zero' has the potential to be a dangerous distraction that reduces the political pressure to achieve actual emission reductions..." "A net zero target means less incentive to get to 'real zero' emissions from fossil fuels, an escape hatch that perpetuates business as usual and delays more meaningful climate action...Rather than gambling on carbon removal technologies of the future, Canada should plan for a managed wind down of fossil fuel production and invest public resources in bona fide solutions like renewables and a just transition from fossil fuels."

Comparison with carbon neutrality

The terms 'climate neutral' and 'net zero' are often used interchangeably by politicians, businesses and even scientists. This graphic lays out the differences between these and related terms.

The terms net zero, carbon neutral, and climate neutral are often used interchangeably. In other contexts, the terms have different meanings from each other.

Whilst different entities have at times treated these terms in different ways, growing consensus is that carbon neutral refers to offsetting all emissions (whilst doing some unspecified degree of reducing emissions) and net zero is shorthand for net zero by 2050, meaning a Paris-aligned reduction pathway as explained above. While similar, carbon neutrality has several key distinctions from net zero:

Carbon credits versus emissions reductions

According to ISO and BSI's carbon neutrality standards, organizations can claim to be "carbon neutral" once they have 1) begun reducing emissions (at any level), 2) created a plan to reduce emissions in the medium-long term as much as possible and 3) have purchased carbon credits to balance remaining emissions. Credible net zero claims, on the other hand, require organizations to reduce emissions as much as possible first, and only then can carbon removal offsets be used to balance remaining emissions. Therefore, carbon neutrality is often considered a more short-term target, with net zero being a longer term target.

Product labels

Another key difference between the two terms according to leading standards and guidance is that products can be certified by official accreditation bodies as carbon neutral but not as net zero. 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.

Perceptions and confusion over net zero versus carbon neutral

Based in large part on the UNFCCC's consistent priority use of the term 'net zero' over 'carbon neutral', there is broad consensus net zero is a more strict standard than carbon neutral, though the precise difference between these terms is sometimes contested. Some authors and recommendations assert the difference between carbon neutral and net zero terms is that carbon neutral solely focuses on carbon dioxide, whereas net zero includes all greenhouse gases. Others have asserted the difference lies in whether or not scope 3 emissions are counted, with only net zero standards requiring they are. A growing number of experts believe carbon neutrality should cover all scopes and greenhouse gases, and the distinction between carbon neutrality and net zero lies only in carbon credit types and use of credits.

See also

• Carbon footprint