Key new insights
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  • Rapid growth in emissions of methane and nitrous oxide — greenhouse gases that are far more powerful than CO2 — are worsening the impact of rising levels of CO2, together putting the world on track for 2.7°C of warming this century.
  • Reducing methane emissions is a key lever available to slow climate change over the next 25 years: readily available, low-cost measures (see implications below) could halve methane emissions by 2030 and must go hand-in-hand with CO2 mitigation and removal efforts to stabilize global temperature in the long term.
  • Rapid reductions in aerosol emissions during the COVID-19 pandemic caused a slight warming of the planet, highlighting the fact that cooling aerosols emitted from fossil fuel combustion to date have partly masked warming from greenhouse gas emissions. While declines in aerosol emissions will improve air quality and benefit the health of billions, this will exacerbate global warming in the short term.
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Key new insights
  • Rapid growth in emissions of methane and nitrous oxide — greenhouse gases that are far more powerful than CO2 — are worsening the impact of rising levels of CO2, together putting the world on track for 2.7°C of warming this century.
  • Reducing methane emissions is a key lever available to slow climate change over the next 25 years: readily available, low-cost measures (see implications below) could halve methane emissions by 2030 and must go hand-in-hand with CO2 mitigation and removal efforts to stabilize global temperature in the long term.
  • Rapid reductions in aerosol emissions during the COVID-19 pandemic caused a slight warming of the planet, highlighting the fact that cooling aerosols emitted from fossil fuel combustion to date have partly masked warming from greenhouse gas emissions. While declines in aerosol emissions will improve air quality and benefit the health of billions, this will exacerbate global warming in the short term.
Insights explained

Powerful greenhouse gases besides CO2 must not be overlooked in efforts to limit global warming to 1.5°C. These include CH4 and N2O, emissions of which are both showing rapid growth, contributing to a pathway to warming well above 2°C.

Methane is the major component of natural gas and is responsible for about 20% of global warming since the pre-industrial era. Emissions of methane reached a record high in 2020, 6% above levels in the year 2000. Human-induced nitrous oxide emissions have grown by 30% over the past three decades. Emissions of both gases from the agricultural sector are the main cause of this large growth. Waste treatment in landfills and fugitive emissions from fossil fuel extraction are also major sources of methane.

Human emissions of aerosols – tiny particles of sulphur or nitrogen emitted during fossil fuel combustion – have an overall cooling effect on the climate. They have partly masked warming from greenhouse gas emissions to date. Emissions of aerosols are predicted to decline, the extent of which depends on pollution-control policies. This will improve air quality and benefit the health of billions of people worldwide but will exacerbate global warming in the short term. This was clearly illustrated during the COVID-19 pandemic: reduced emissions of cooling aerosols during national lockdowns led to a temperature rise of 0.03°C globally and up to 0.3°C at higher northern hemisphere latitudes in May 2020.

Overall, largely due to a growth in methane and nitrous oxide emissions alongside declines in aerosols, non-CO2 factors have increasingly warmed the climate over the past 20 years. Ongoing increases in non-CO2 greenhouse gases and declines in aerosols will reduce the remaining carbon budget.

The good news is that readily available and low-cost measures could reduce the projected anthropogenic methane emissions by more than 45% to 2030. Due to the short lifetime of methane in the atmosphere, addressing the sources of methane emissions will have a rapid impact on climate change.

“Low-hanging fruit” options include reducing fossil fuel leaks and improving waste treatment technologies, which alone could avoid 0.3°C of warming by the 2040s. There are also solutions in the food and agricultural sector that could reduce nitrous oxide and methane emissions – a mix of supply and demand options – such as increasing the efficiency of nitrogen use, further improvement and uptake of feedstocks that reduce the methane emissions of ruminants, promotion of healthy low-meat diets and reduction of food waste. These solutions come with additional health and environmental benefits.

Insights explained

Powerful greenhouse gases besides CO2 must not be overlooked in efforts to limit global warming to 1.5°C. These include CH4 and N2O, emissions of which are both showing rapid growth, contributing to a pathway to warming well above 2°C.

Methane is the major component of natural gas and is responsible for about 20% of global warming since the pre-industrial era. Emissions of methane reached a record high in 2020, 6% above levels in the year 2000. Human-induced nitrous oxide emissions have grown by 30% over the past three decades. Emissions of both gases from the agricultural sector are the main cause of this large growth. Waste treatment in landfills and fugitive emissions from fossil fuel extraction are also major sources of methane.

Human emissions of aerosols – tiny particles of sulphur or nitrogen emitted during fossil fuel combustion – have an overall cooling effect on the climate. They have partly masked warming from greenhouse gas emissions to date. Emissions of aerosols are predicted to decline, the extent of which depends on pollution-control policies. This will improve air quality and benefit the health of billions of people worldwide but will exacerbate global warming in the short term. This was clearly illustrated during the COVID-19 pandemic: reduced emissions of cooling aerosols during national lockdowns led to a temperature rise of 0.03°C globally and up to 0.3°C at higher northern hemisphere latitudes in May 2020.

Overall, largely due to a growth in methane and nitrous oxide emissions alongside declines in aerosols, non-CO2 factors have increasingly warmed the climate over the past 20 years. Ongoing increases in non-CO2 greenhouse gases and declines in aerosols will reduce the remaining carbon budget.

The good news is that readily available and low-cost measures could reduce the projected anthropogenic methane emissions by more than 45% to 2030. Due to the short lifetime of methane in the atmosphere, addressing the sources of methane emissions will have a rapid impact on climate change.

“Low-hanging fruit” options include reducing fossil fuel leaks and improving waste treatment technologies, which alone could avoid 0.3°C of warming by the 2040s. There are also solutions in the food and agricultural sector that could reduce nitrous oxide and methane emissions – a mix of supply and demand options – such as increasing the efficiency of nitrogen use, further improvement and uptake of feedstocks that reduce the methane emissions of ruminants, promotion of healthy low-meat diets and reduction of food waste. These solutions come with additional health and environmental benefits.

Background
Global warming is driven by human activities that produce both positive and negative climate forcing. Overall, about 21% of current net global warming is caused by factors other than CO2. These include emissions of other greenhouse gases, their precursors or warming aerosols such as black carbon. Non-CO2 factors driving global warming arise primarily from the burning of fossil fuels, and from land-use including agricultural activities (see image for a full breakdown). They have had an increasing warming effect over the past 20 years, largely due to growth in emissions of the powerful greenhouse gases methane and nitrous oxide. This is worsening the impact of rising levels of CO2. If anthropogenic emissions of methane and nitrous oxide continue to rise, it will reduce the remaining carbon budget, preventing stabilization of global temperature once net-zero emissions of CO2 are reached.
Background
Global warming is driven by human activities that produce both positive and negative climate forcing. Overall, about 21% of current net global warming is caused by factors other than CO2. These include emissions of other greenhouse gases, their precursors or warming aerosols such as black carbon. Non-CO2 factors driving global warming arise primarily from the burning of fossil fuels, and from land-use including agricultural activities (see image for a full breakdown). They have had an increasing warming effect over the past 20 years, largely due to growth in emissions of the powerful greenhouse gases methane and nitrous oxide. This is worsening the impact of rising levels of CO2. If anthropogenic emissions of methane and nitrous oxide continue to rise, it will reduce the remaining carbon budget, preventing stabilization of global temperature once net-zero emissions of CO2 are reached.
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Implications

At national and local levels, decision makers in government and the private sector are urged to:

  • reduce fugitive methane emissions from the fossil fuel sector through regulation – for example certification of suppliers, and through investment in new technologies for leak detection and repair, including in production, transmission and distribution systems;
  • reduce net emissions from landfill by promoting the separation of waste at source, recycling, incineration with energy recovery and anaerobic digestion with biogas recovery;
  • curtail methane emissions from the food and agriculture sectors through a broad portfolio of policies to reduce food waste and improve land and livestock management – for example promoting the use of lower emission feedstock, improving water management in rice cultivation and encouraging healthy, low-meat diets;
  • reduce nitrous oxide emissions in agriculture through practices that limit the use of nitrogen fertilizers and promote their efficient use – for example through improved timing of nitrogen application and better management of animal manure.
Image
Implications

At national and local levels, decision makers in government and the private sector are urged to:

  • reduce fugitive methane emissions from the fossil fuel sector through regulation – for example certification of suppliers, and through investment in new technologies for leak detection and repair, including in production, transmission and distribution systems;
  • reduce net emissions from landfill by promoting the separation of waste at source, recycling, incineration with energy recovery and anaerobic digestion with biogas recovery;
  • curtail methane emissions from the food and agriculture sectors through a broad portfolio of policies to reduce food waste and improve land and livestock management – for example promoting the use of lower emission feedstock, improving water management in rice cultivation and encouraging healthy, low-meat diets;
  • reduce nitrous oxide emissions in agriculture through practices that limit the use of nitrogen fertilizers and promote their efficient use – for example through improved timing of nitrogen application and better management of animal manure.
46%
share of warming factors driving climate change other than CO2 (cooling factors offset a proportion of this, leading to 21% of net warming).
0.03°C
short-term global warming as a result of COVID-19 restrictions.
45%

methane emission reductions possible by 2030 through readily available and low-cost measures (see implications).

46%
share of warming factors driving climate change other than CO2 (cooling factors offset a proportion of this, leading to 21% of net warming).
0.03°C
short-term global warming as a result of COVID-19 restrictions.
45%

methane emission reductions possible by 2030 through readily available and low-cost measures (see implications).

Image
Figure 2. Current human-driven factors that contribute to global warming and cooling. The factors are partitioned by their direct and indirect sources: factors driven by land-use including agricultural activities (left column) and fossil fuel combustion (right column). The atmospheric gases include both long- and short-lived types (see Martin et al., 2021 for references). Abbreviations are: CO2 – carbon dioxide; N2O – nitrous oxide; CH4 – methane; Trop. O3 – tropospheric ozone; SOx – sulphate aerosols; NOx – nitrogen oxides; LUC albedo – changes in the reflectivity of land surface due to land-use changes.
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Figure 2. Current human-driven factors that contribute to global warming and cooling. The factors are partitioned by their direct and indirect sources: factors driven by land-use including agricultural activities (left column) and fossil fuel combustion (right column). The atmospheric gases include both long- and short-lived types (see Martin et al., 2021 for references). Abbreviations are: CO2 – carbon dioxide; N2O – nitrous oxide; CH4 – methane; Trop. O3 – tropospheric ozone; SOx – sulphate aerosols; NOx – nitrogen oxides; LUC albedo – changes in the reflectivity of land surface due to land-use changes.
Browse insights in climate

Browse insights in climate


10 New Insights in Climate Science

A year of climate-related science in review

Each year we consult researchers and carry out a horizon scan in fields related to climate change on what the latest findings and most important new emerging fields are. We summarize this in 10 important scientific insights, and the result has always been a rich and valuable scientific synthesis for policy and society at large, a testament to the ever-expanding and improving knowledge of our planetary climate systems and the interactions with the human world.
Download PDF

Extras

Acknowledgements

The full authoring team and other contributors are listed here. The making of this report has been led by Future Earth, The Earth League and the World Climate Research Programme (WCRP). We also gratefully acknowledge support from Arizona State University (ASU), GERICS Climate Service Center Germany (an institution of Helmholtz-Zentrum Hereon),

 We acknowledge the work of the following individuals in their respective capacities:

Produced by: Future Earth, The Earth League, Azote, and the World Climate Research Programme
Website, graphics and publication design: Cultivate Communications, Azote

10 New Insights in Climate Science

A year of climate-related science in review

Each year we consult researchers and carry out a horizon scan in fields related to climate change on what the latest findings and most important new emerging fields are. We summarize this in 10 important scientific insights, and the result has always been a rich and valuable scientific synthesis for policy and society at large, a testament to the ever-expanding and improving knowledge of our planetary climate systems and the interactions with the human world.
Download PDF

Extras

Acknowledgements

The making of this report has been led by Future Earth, The Earth League and the World Climate Research Programme (WCRP). We also gratefully acknowledge support from Arizona State University (ASU), GERICS Climate Service Center Germany (an institution of Helmholtz-Zentrum Hereon),

 We acknowledge the work of the following individuals in their respective capacities:

Produced by: Future Earth, The Earth League, and the World Climate Research Programme
Website, graphics and publication design: Cultivate Communications