Net-zero emissions

• 1. Introduction

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  By November 2023, around 145 countries had announced or were considering net-zero targets for their greenhouse gas emissions. Country-level targets now cover 92% of global GDP, 88% of all global emissions, and 89% of the world's population. Net-zero is also the stated goal of 65% of the world's 2,000 largest publicly traded companies. Yet most of these commitments have low credibility. While 61% of global carbon dioxide emissions are covered by some net-zero target, credible targets cover only 7%. What does it actually mean to commit to net zero? What separates a genuine target from an accounting exercise? And how did this concept become the dominant framework of global climate politics?

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• 2. Origins in Science

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  The concept of net-zero emissions emerged from scientific research in the late 2000s. Scientists studying how the atmosphere, oceans, and carbon cycle were reacting to CO2 emissions reached a stark conclusion. Global warming would significantly slow down only if human-caused emissions reached zero. Even then, existing greenhouse gases already in the atmosphere would continue contributing to some warming. The Paris Agreement of 2015 translated this science into a formal international commitment. It called for balancing human-caused greenhouse gas emissions with removals by natural and artificial sinks, to be achieved in the second half of this century.

  The term net-zero gained broad currency after October 2018. That month, the Intergovernmental Panel on Climate Change published its Special Report on Global Warming of 1.5 °C. The report stated with high confidence that reaching and sustaining net-zero global CO2 emissions would halt human-caused global warming on multi-decadal timescales. Four months earlier, in June 2018, a scientific review had appeared with the title "Net-zero emissions energy systems." It was the first to assess the particular challenges of not just reducing energy-related emissions but eliminating them entirely.

  The 1992 Rio Convention had used a different concept: stabilization of greenhouse gas concentrations in the atmosphere. Net-zero and stabilization are not the same target. Under stabilization, some ongoing emissions remain acceptable, but global temperatures would continue rising over many centuries due to the ocean's delayed response to warming. At net-zero CO2 emissions, by contrast, atmospheric concentrations would actually decline. They would fall 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. That fundamental distinction between stabilization and net-zero shapes every debate about which gases need to reach zero, and by when.

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• 3. CO2 and Its Cousins

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  Methane, nitrous oxide, and fluorinated gases all trap heat in the atmosphere, but they do not behave the same way CO2 does. Short-lived gases like methane do not accumulate in the climate system the way CO2 does. Reductions in methane emissions produce an almost immediate decline in the warming they cause. That means reducing them to zero is not strictly necessary to halt global warming.

  Methane from farming is among the emissions that climate modellers consider hardest to phase out entirely. For this reason, reaching net-zero for all greenhouse gases combined is expected to take longer than reaching it for CO2 alone. But the short-term potency of these gases poses its own danger. They could push global temperatures past the 1.5 °C threshold much earlier than projections based on CO2 alone would suggest. A comprehensive net-zero target covers all greenhouse gases; robust standards say that full coverage is essential.

  France, in its national climate strategy, uses the term "carbon neutral" to mean net reductions of all greenhouse gases. The United States pledged net-zero by 2050. As of March 2021, it had not specified which gases would fall under that commitment. Organizations that make net-zero pledges often plan to offset remaining emissions by purchasing carbon credits, a practice that has generated sustained and serious controversy.

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• 4. The Offset Problem

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  Kevin Smith, writing in a 2007 report from the Transnational Institute, compared carbon offsets to medieval indulgences. He argued that paying offset companies to handle emissions allows organizations to maintain what he called a "business as usual" attitude. That approach, he said, stifled the major structural changes that real decarbonization requires. His criticism has proven durable. A 2021 watchdog ruling against Shell found that offsets had played a part in greenwashing. That ruling reinforced the case that carbon credits can serve as cover rather than cure.

  The United Nations has operated a certification process for carbon offsets since 2001, through the Clean Development Mechanism. Its stated aim is to stimulate sustainable development and emissions reductions while giving industrialized countries flexibility in meeting their reduction targets. Yet most carbon credits on voluntary markets today do not meet UN, UNFCCC, ISO, or Science Based Targets initiative standards. They fall short of what those standards require for permanent carbon dioxide removals. The difficulty of calculating genuine sequestration has made the market particularly susceptible to weak or fraudulent claims.

  The ISO and BSI standards for carbon neutrality take a notably weaker approach than their net-zero counterparts. Carbon neutrality standards allow avoided-emissions credits: funding for actions that emit less than a hypothetical baseline, without removing anything from the atmosphere. Net-zero standards, by contrast, require that removals match the permanence of the gases they balance. Tzeporah Berman, chair of the Fossil Fuel Non-Proliferation Treaty Initiative, called such claims by fossil fuel companies "delusional and based on bad science."

  Non-native and monocultural forest plantations have attracted particular criticism as offset projects. Their effects on native biodiversity have been described as "limited and at times negative." At the 2022 United Nations Climate Change Conference, the UN High-Level Expert Group on net-zero commitments issued 10 recommendations for non-state actors. The group had been formed by Secretary-General António Guterres and was chaired by former Canadian Environment Minister Catherine McKenna. Among the recommendations: non-state actors should publicly disclose verifiable information that substantiates compliance with their pledges. Significant investment in carbon capture and permanent geological storage will most likely be necessary to achieve net-zero targets by mid-century.

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• 5. Scopes, Standards, and Accountability

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  The Greenhouse Gas Protocol organizes corporate emissions into three categories called scopes. Scope 1 covers all direct emissions within a company's own boundary: fuel it burns, its vehicle fleet, and fugitive releases from its processes. Scope 2 captures indirect emissions from purchased electricity, heat, cooling, and steam. As of 2010, at least one third of all global greenhouse gas emissions were estimated to fall under Scope 2. Scope 3 is the broadest category, covering the full value chain: suppliers, customers, transportation, and the emissions generated when a company's products are ultimately used.

  Scope 3 emissions were estimated to represent 75% of all emissions reported to the Carbon Disclosure Project. That percentage varies significantly across business sectors. The breadth of Scope 3 makes it the most consequential scope to include, and also the most convenient to exclude. Some oil companies claim net-zero for their Scope 1 and 2 operations. They exclude the emissions produced when their oil is burned by customers. Those end-use emissions typically represent 70-90% of total oil-related emissions. Robust net-zero standards require Scope 3 to be counted; carbon-neutrality standards do not.

  The Science Based Targets initiative holds that residual emissions across most sectors should fall below 10% of an organization's baseline by 2050. For the power sector, where competitive low-carbon alternatives already exist, the bar is set even lower. For harder-to-abate sectors like heavy manufacturing and chemicals, some higher residual fraction may remain acceptable. To date, 27 countries have enacted domestic net-zero legislation. Switzerland is among those currently developing laws that would extend requirements to companies based within their borders.

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• 6. Costs and Consequences

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  The International Monetary Fund estimated that shifting to net-zero policies by 2050 would leave global GDP about 7% higher than under current government policies. The cost of the emissions reductions themselves would amount to less than 2% of world GDP in 2050. The savings from reduced climate damage would be approximately 9% of world GDP. That arithmetic has not silenced the debate.

  The International Energy Agency identified a specific threshold. Global investment in low-carbon substitutes for fossil fuels would need to reach $4 trillion annually by 2030 for the world to reach net-zero by 2050. Some analyses have raised concerns that worldwide net-zero by mid-century may not be achievable. In EU member states, on average around 29% of companies have formulated a net-zero target or already achieved it. Those figures vary significantly across industries and firm sizes.

  Climate scientists James Dyke, Bob Watson, and Wolfgang Knorr traced the history of climate policy failures from 1988 to 2021. Their conclusion was stark: the idea of net-zero has functioned as what they called a "blank cheque" for continued fossil fuel use. By allowing actors to defer present-day emissions reductions in favor of unproven future technologies, it licensed a "burn now, pay later" approach. Carbon emissions continued to rise. They concluded that current net-zero policies were never intended to keep warming within 1.5 °C. The policies were driven, they argued, by protecting business as usual, not the climate.

  In the United Kingdom, the transition to net zero carries uneven regional consequences. London and the South East hold more jobs in service industries likely to be less affected. The Midlands and the North, where heavy industry is concentrated, face greater disruption. Some cattle farmers are lobbying for GWP*, an alternative accounting approach that critics have called "dangerous."

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