Greenhouse gas emissions là gì

September 17, 2019 By Kelly Levin, Taryn Fransen, Clea Schumer and Chantal Davis Cover Image by: Aaron Minnick/

Editor"s Note: This article was updated in May 2021 to include’s latest research and information about new national net-zero targets.

The latest research is clear: To avoid the worst climate impacts, global greenhouse gas (GHG) emissions will need to drop by half by 2030 and reach net-zero around mid-century.

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Recognizing this urgency, a rapidly growing number of national government, local government and business leaders are making commitments to reach net-zero emissions within their jurisdictions or businesses. To date, over fifty countries have communicated such “net-zero targets,” including the world’s largest emitters (China and the United States). On top of that, hundreds more regions, cities and businesses have set targets of their own.

These numbers are climbing quickly, particularly because the U.N. Secretary General asked countries to come forward with net-zero targets. The U.N. High Level Climate Champions’ Race to Zero campaign also calls on regions, cities, businesses, investors and civil society to submit plans to reach net-zero emissions by 2050 in advance of the United Nations climate negotiations (COP 26) in Glasgow in November 2021.

But what does a net-zero target mean, what’s the science behind net-zero and which countries have already made such commitments? Here are nine common questions and answers about net zero:

1. What Does It Mean to Reach Net-Zero Emissions?

Net-zero emissions will be achieved when all GHG emissions released by humans are counterbalanced by removing GHGs from the atmosphere in a process known as carbon removal.

First and foremost, human-caused emissions (such as those from fossil-fueled vehicles and factories) should be reduced as close to zero as possible. Any remaining GHGs should then be balanced with an equivalent amount of carbon removal, which can happen through things like restoring forests or using direct air capture and storage (DACS) technology. Reaching net-zero emissions is akin to achieving "climate neutrality."


The Special Report on Global Warming of 1.5˚C, from the Intergovernmental Panel on Climate Change (IPCC), finds that if the world reaches net-zero emissions by 2040, the chance of limiting warming to 1.5 degrees C is considerably higher. The sooner emissions peak, and the lower they are at that point, the more realistic achieving net zero becomes. This would also create less reliance on carbon removal in the second half of the century.

This does not suggest that all countries need to reach net-zero emissions at the same time. The chances of limiting warming to 1.5 degrees C, however, depend significantly on how soon the highest emitters reach net-zero emissions. Equity-related considerations — including responsibility for past emissions, equality in per-capita emissions and capacity to act — also suggest earlier dates for wealthier, higher-emitting countries.

Importantly, the time frame for reaching net-zero emissions is different for CO2 alone versus for CO2 plus other GHGs like methane, nitrous oxide and fluorinated gases. For non-CO2 emissions, the net zero date is later because models suggest that some of these emissions — such as methane from agricultural sources — are more difficult to phase out. However, these potent but short-lived gases will drive temperatures higher in the near-term, potentially pushing temperature change past the 1.5 degrees C threshold much earlier.

Because of this, it"s important for countries to specify whether their net-zero targets cover CO2 only or all GHGs. A comprehensive net-zero emissions target would include all GHGs, ensuring that non-CO2 gases are also reduced.

3. What Needs to Happen to Achieve Net-Zero Emissions?

Policy, technology and behavior need to shift across the board. For example, in pathways to 1.5 degrees C, renewables are projected to supply 70-85% of electricity by 2050. Energy efficiency and fuel-switching measures are critical for transportation. Improving the efficiency of food production, changing dietary choices, halting deforestation, restoring degraded lands and reducing food loss and waste also have significant potential to reduce emissions.


In some cases, emissions are actually getting worse. Despite tremendous acceleration in renewable energy, adoption will need to increase by a factor of five to reach 2030 and 2050 goals. Current rates of renovation for both residential and commercial buildings, for instance, fall between 1% and 2% per year on average, whereas they need to reach 2.5-3.5% per year by 2030. And the world needs to drastically slow deforestation and increase tree cover gain five times faster by 2030.

5. How Many Countries Have Net-Zero Targets?

Global momentum for web10_setting net-zero targets is growing quickly, with key economies like China, the United States and the European Union articulating such commitments. Bhutan was the first country to set a net-zero target in 2015. Now over 50 countries, representing more than half of global emissions, have set a net-zero target.

Climate Watch’s Net-Zero Tracker shows how these targets were set, such as through nationally determined contributions (NDCs), long-term low GHG emissions development strategies (LTS), domestic laws,policies or high-level political pledges from heads of state or other cabinet members.

6. Why and How Should Countries Align Their 2030 Emissions-Reduction Targets with a Net-Zero Emissions Goal?

When beginning a journey to reach net-zero emissions by mid-century, countries must pursue near-term action with their long-term objectives in mind. This will help avoid locking in carbon-intensive, non-resilient infrastructure and technologies. Countries can also cut near- and long-term costs by investing in green infrastructure that will not need to be phased out later, designing consistent policies and sending strong signals to the private sector to invest in climate action.

Under the Paris Agreement, countries agreed to submit climate plans every five years, known as nationally determined contributions, or NDCs. NDCs are an important tool to align near- and long-term goals. When informed by a country’s long-term vision, these documents can help governments implement the types of policies, signals, targets and other enhancement strategies necessary in the nearer term to realize an ambitious mid-century objective.

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Many countries with net-zero targets are beginning to incorporate them directly into their near-term NDCs. These targets are also being expressed in many countries across other law and policy documents. The most advantageous action, ultimately, will be for countries to express their net-zero commitments in as many source documents as possible, including NDCs. This will make the target as durable and binding as possible, allowing for synergistic planning.

7. Does the Paris Agreement Commit Countries to Achieving Net-Zero Emissions?

In short, yes. However, while the Paris Agreement establishes a global goal that implies reaching net-zero emissions, it was left unresolved when individual countries should reach that goal.

The Paris Agreement sets a long-term goal of achieving "a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century, on the basis of equity, and in the context of sustainable development and efforts to eradicate poverty." This concept of balancing emissions and removals is akin to reaching net-zero emissions.

The Paris Agreement also commits governments to putting forward plans to sharply reduce emissions and ramp up efforts to reach net-zero emissions. The Paris Agreement’s invitation to countries to submit long-term, low-emissions development strategies by COP 26 is one opportunity for countries to set net-zero targets and chart how they aim to make such transitions.

Ultimately, commitments to create bold short- and long-term targets that align with a net-zero emissions future send important signals to all levels of government, the private sector and the public that leaders are betting on a safe and prosperous future.

8. Are Net-Zero Targets a Form of Greenwashing?

No, but they can be if used as an excuse to not take bold climate action in the near-term.

Although net-zero targets continue to gain traction with governments and companies, skeptical voices have emerged, from academic journals to campaign groups to Greta Thunberg’s speech in Davos. Critiques of net-zero targets include:

a. The “net” aspect of net-zero targets could dampen efforts to rapidly cut emissions.

Critics are concerned that this could foster an overreliance on carbon dioxide removal, allowing decision-makers to use net-zero targets to avoid emission reductions in the near-term. Decision-makers can address this concern by web10_setting absolute reduction targets (targets that do not rely on removals) alongside their longer-term net reduction targets.

b. Some countries’ net-zero targets rely on purchasing emissions reductions, delaying reductions within their own boundaries.

Some countries are web10_setting net-zero targets that rely on investing in or paying for emissions reductions from other countries to use toward their own targets. There’s concern that government leaders might use this strategy to avoid reducing their own emissions in the long-term. Decision-makers can address this concern by web10_setting deep emission reduction targets that explicitly avoid or limit using offsets to achieve their goals.

c. The time horizon for net-zero targets — typically 2050 — feels distant.

Today’s infrastructure can last for decades and have a major impact on mid-century targets. Decision-makers must take this into account by establishing near- and mid-term milestones for their path to net-zero emissions, including by web10_setting ambitious 2030 emission reduction targets as part of their NDCs. NDCs are subject to transparency and accountability mechanisms under the Paris Agreement that can foster implementation in the near term, which is critical for a long-term net-zero goal to be credible.

In short, net-zero commitments must be robust to be effective and advance climate action. Countries must take concrete steps to set robust targets.