posts: 45124
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| 45124 | what share of global CO2 emissions come from aviation? | untitled-reusable-block-289 | wp_block | publish | <!-- wp:paragraph --> <p>Flying is a highly controversial topic in climate debates. There are a few reasons for this. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The first is the disconnect between its role in our personal and collective carbon emissions. Air travel dominates a frequent traveller's individual contribution to climate change. Yet aviation overall accounts for only 2.5% of global carbon dioxide (CO<sub>2</sub>) emissions. This is because there are large inequalities in how much people fly – many do not, or cannot afford to, fly at all.{ref}The best estimates put this figure at around 80% of the world population. We look at this in more detail in our article "<a href="https://ourworldindata.org/carbon-footprint-flying">Where in the world do people have the highest CO2 emissions from flying?</a>"{/ref}</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The second is how aviation emissions are attributed to countries. CO<sub>2</sub> emissions from domestic flights <em>are</em> counted in a country’s emission accounts. International flights are not – instead they are counted as their own category: ‘bunker fuels’. The fact that they don’t count towards the emissions of any country means there are few incentives for countries to reduce them.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>It’s also important to note that unlike the most common greenhouse gases – carbon dioxide, methane or nitrous oxide – non-CO<sub>2</sub> forcings from aviation <em>are not included</em> in the Paris Agreement. This means they could be easily overlooked – especially since international aviation is not counted within any country’s emissions inventories or targets.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>How much of a role does aviation play in global emissions and climate change? In this article we take a look at the key numbers that are useful to know.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Global aviation (including domestic and international; passenger and freight) accounts for:</p> <!-- /wp:paragraph --> <!-- wp:list --> <ul><li><strong>1.9%</strong> of <a href="https://ourworldindata.org/ghg-emissions-by-sector">greenhouse gas emissions</a> (which includes all greenhouse gases, not only CO<sub>2</sub>)</li><li><strong>2.5%</strong> of CO<sub>2</sub> emissions</li><li><strong>3.5%</strong> of 'effective radiative forcing' – a closer measure of its impact on warming.</li></ul> <!-- /wp:list --> <!-- wp:paragraph --> <p>The latter two numbers refer to 2018, and the first to 2016, the latest year for which such data are available.</p> <!-- /wp:paragraph --> <!-- wp:separator --> <hr class="wp-block-separator"/> <!-- /wp:separator --> <!-- wp:heading {"level":4} --> <h4>Aviation accounts for 2.5% of global CO<sub>2</sub> emissions</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>As we will see later in this article, there are a number of processes by which aviation contributes to climate change. But the one that gets the most attention is its contribution via CO<sub>2</sub> emissions. Most flights are powered by jet gasoline – although some partially run on biofuels – which is converted to CO<sub>2</sub> when burned. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>In a recent paper, researchers – David Lee and colleagues – reconstructed annual CO<sub>2 </sub>emissions from global aviation dating back to 1940.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., ... & Gettelman, A. (2020). <a href="https://www.sciencedirect.com/science/article/pii/S1352231020305689">The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018</a>. <em>Atmospheric Environment</em>, 117834.{/ref} This was calculated based on fuel consumption data from the International Energy Agency (IEA), and earlier estimates from Robert Sausen and Ulrich Schumann (2000).{ref}Sausen, R., & Schumann, U. (2000). <a href="https://link.springer.com/article/10.1023/A:1005579306109">Estimates of the climate response to aircraft CO2 and NOx emissions scenarios</a>. <em>Climatic Change</em>, <em>44</em>(1-2), 27-58.{/ref}</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The time series of global emissions from aviation since 1940 is shown in the accompanying chart. In 2018, it’s estimated that global aviation – which includes both passenger and freight – emitted 1.04 billion tonnes of CO<sub>2</sub>.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>This represented 2.5% of <a href="https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels" data-type="URL" data-id="https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels">total CO<sub>2</sub> emissions</a> in 2018.{ref}The Global Carbon Budget estimated total CO<sub>2</sub> emissions from all fossil fuels, cement production and land-use change to be 42.1 billion tonnes in 2018. This means aviation accounted for [1 / 42.1 * 100] = 2.5% of total emissions.{/ref}<sup>,</sup>{ref}Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project. <a href="https://doi.org/10.18160/gcp-2019">https://doi.org/10.18160/gcp-2019</a>.<br><br>If we were to exclude land use change emissions, aviation accounted for 2.8% of fossil fuel emissions. The Global Carbon Budget estimated total CO<sub>2</sub> emissions from fossil fuels and cement production to be 36.6 billion tonnes in 2018. This means aviation accounted for [1 / 36.6 * 100] = 2.8% of total emissions.{/ref}</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Aviation emissions have doubled since the mid-1980s. But, they’ve been growing at a similar rate as total CO<sub>2</sub> emissions – this means its share of global emissions has been relatively stable: in the range of 2% to 2.5%.{ref}2.3% to 2.8% of emissions if land use is excluded.{/ref}</p> <!-- /wp:paragraph --> <!-- wp:image {"id":36836,"sizeSlug":"large"} --> <figure class="wp-block-image size-large"><img src="https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-693x550.png" alt="" class="wp-image-36836"/></figure> <!-- /wp:image --> <!-- wp:heading {"level":4} --> <h4>Non-CO<sub>2</sub> climate impacts mean aviation accounts for 3.5% of global warming</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>Aviation accounts for around 2.5% of global CO<sub>2</sub> emissions, but it’s overall contribution to climate change is higher. This is because air travel does not only emit CO<sub>2</sub>: it affects the climate in a number of more complex ways.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>As well as emitting CO<sub>2</sub> from burning fuel, planes affect the concentration of other gases and pollutants in the atmosphere. They result in a short-term increase, but long-term decrease in ozone (O<sub>3</sub>); a decrease in methane (CH<sub>4</sub>); emissions of water vapour; soot; sulfur aerosols; and water contrails. While some of these impacts result in warming, others induce a cooling effect. Overall, the warming effect is stronger.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>David Lee et al. (2020) quantified the overall effect of aviation on global warming when all of these impacts were included.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., ... & Gettelman, A. (2020). <a href="https://www.sciencedirect.com/science/article/pii/S1352231020305689">The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018</a>. <em>Atmospheric Environment</em>, 117834.{/ref} To do this they calculated the so-called ‘Radiative Forcing’. Radiative forcing measures the difference between incoming energy and the energy radiated back to space. If more energy is absorbed than radiated, the atmosphere becomes warmer. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>In their chart we see <a href="https://ars.els-cdn.com/content/image/1-s2.0-S1352231020305689-gr3_lrg.jpg" target="_blank" rel="noreferrer noopener">their estimates for the radiative forcing</a> of the different elements. When we combine them, aviation accounts for approximately 3.5% of effective radiative forcing: that is, 3.5% of warming.<br><br>Although CO<sub>2 </sub>gets most of the attention, it accounts for less than half of this warming. Two-thirds (66%) comes from non-CO<sub>2 </sub>forcings. Contrails – water vapor trails from aircraft exhausts – account for the largest share.</p> <!-- /wp:paragraph --> <!-- wp:heading {"level":4} --> <h4>We don’t yet have the technologies to decarbonize air travel</h4> <!-- /wp:heading --> <!-- wp:paragraph --> <p>Aviation’s contribution to climate change – 3.5% of warming, or 2.5% of CO<sub>2</sub> emissions – is often less than people think. It’s currently a relatively small chunk of emissions compared to other sectors. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The key challenge is that it is particularly hard to decarbonize. We have solutions to reduce emissions for many of the <a href="https://ourworldindata.org/ghg-emissions-by-sector">largest emitters</a> – such as power or road transport – and it’s now a matter of scaling them. We can deploy renewable and nuclear energy technologies, and transition to electric cars. But we don’t have proven solutions to tackle aviation yet. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>There are some design concepts emerging – Airbus, for example, <a href="https://web.archive.org/web/20201031121346/https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html" data-type="URL" data-id="https://web.archive.org/web/20201031121346/https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html">have announced plans</a> to have the first zero-emission aircraft by 2035, using hydrogen fuel cells. Electric planes may be a viable concept, but are likely to be limited to very small aircraft due to the limitations of battery technologies and capacity. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Innovative solutions may be on the horizon, but they’re likely to be far in the distance.</p> <!-- /wp:paragraph --> <!-- wp:owid/prominent-link {"title":"Towards zero-carbon transport: how can we expect the sector’s CO\u003csub\u003e2\u003c/sub\u003e emissions to change in the future?","linkUrl":"ourworldindata.org/co2-emissions-from-transport","mediaId":36827,"mediaUrl":"https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070.png","mediaAlt":"","className":"is-style-thin"} --> <!-- wp:paragraph --> <p></p> <!-- /wp:paragraph --> <!-- /wp:owid/prominent-link --> <!-- wp:owid/additional-information {"defaultOpen":true} --> <!-- wp:heading {"level":3} --> <h3>Appendix: <strong>Efficiency improvements means air traffic has increased more rapidly than emissions</strong></h3> <!-- /wp:heading --> <!-- wp:columns {"className":"is-style-sticky-right"} --> <div class="wp-block-columns is-style-sticky-right"><!-- wp:column --> <div class="wp-block-column"><!-- wp:paragraph --> <p>Global emissions from aviation have increased a lot over the past half-century. However, air travel volumes increased even more rapidly. </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>Since 1960, aviation emissions increased almost seven-fold; since 1970 they’ve tripled. Air traffic volume – here defined as revenue passenger kilometers (RPK) traveled – <a href="https://ourworldindata.org/grapher/airline-capacity-and-traffic">increased by orders of magnitude more</a>: almost 300-fold since 1950; and 75-fold since 1960.{ref}Airline traffic data comes from the International Civil Aviation Organization (ICAO) via <a href="https://www.airlines.org/dataset/world-airlines-traffic-and-capacity">Airlines for America</a>. Revenue passenger kilometers (RPK) measures the number of paying passengers multiplied by their distance traveled.{/ref} </p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The much slower growth in emissions means aviation efficiency has seen massive improvements. In the chart we show both the increase in global airline traffic since 1950, and aviation efficiency, measured as the quantity of CO<sub>2</sub> emitted per revenue passenger kilometer traveled. In 2018, approximately 125 grams of CO<sub>2 </sub> were emitted per RPK. In 1960, this was eleven-fold higher; in 1950 it was twenty-fold higher. Aviation has seen massive efficiency improvements over the past 50 years.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>These improvements have come from several sources: improvements in the design and technology of aircraft; larger aircraft sizes (allowing for more passengers per flight); and an increase in how ‘full’ passenger flights are. This last metric is termed the ‘passenger load factor’. The passenger load factor measures the actual number of kilometers traveled by paying customers (RPK) as a percentage of the available seat kilometers (ASK) – the kilometers traveled if every plane was full. If every plane was full the passenger load factor would be 100%. If only three-quarters of the seats were filled, it would be 75%.</p> <!-- /wp:paragraph --> <!-- wp:paragraph --> <p>The global passenger load factor <a href="https://ourworldindata.org/grapher/airline-passenger-load-factor">increased from 61% in 1950 to 82% in 2018</a>. </p> <!-- /wp:paragraph --></div> <!-- /wp:column --> <!-- wp:column --> <div class="wp-block-column"><!-- wp:image {"id":36837,"sizeSlug":"large"} --> <figure class="wp-block-image size-large"><img src="https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-800x505.png" alt="" class="wp-image-36837"/></figure> <!-- /wp:image --></div> <!-- /wp:column --></div> <!-- /wp:columns --> <!-- /wp:owid/additional-information --> | {
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2021-09-24 12:39:06 | 2024-02-16 14:23:02 | [
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2021-09-24 13:39:17 | 2023-06-29 12:08:45 | {} |
Flying is a highly controversial topic in climate debates. There are a few reasons for this. The first is the disconnect between its role in our personal and collective carbon emissions. Air travel dominates a frequent traveller's individual contribution to climate change. Yet aviation overall accounts for only 2.5% of global carbon dioxide (CO2) emissions. This is because there are large inequalities in how much people fly – many do not, or cannot afford to, fly at all.{ref}The best estimates put this figure at around 80% of the world population. We look at this in more detail in our article "[Where in the world do people have the highest CO2 emissions from flying?](https://ourworldindata.org/carbon-footprint-flying)"{/ref} The second is how aviation emissions are attributed to countries. CO2 emissions from domestic flights _are_ counted in a country’s emission accounts. International flights are not – instead they are counted as their own category: ‘bunker fuels’. The fact that they don’t count towards the emissions of any country means there are few incentives for countries to reduce them. It’s also important to note that unlike the most common greenhouse gases – carbon dioxide, methane or nitrous oxide – non-CO2 forcings from aviation _are not included_ in the Paris Agreement. This means they could be easily overlooked – especially since international aviation is not counted within any country’s emissions inventories or targets. How much of a role does aviation play in global emissions and climate change? In this article we take a look at the key numbers that are useful to know. Global aviation (including domestic and international; passenger and freight) accounts for: * **1.9%** of [greenhouse gas emissions](https://ourworldindata.org/ghg-emissions-by-sector) (which includes all greenhouse gases, not only CO2) * **2.5%** of CO2 emissions * **3.5%** of 'effective radiative forcing' – a closer measure of its impact on warming. The latter two numbers refer to 2018, and the first to 2016, the latest year for which such data are available. ## Aviation accounts for 2.5% of global CO2 emissions As we will see later in this article, there are a number of processes by which aviation contributes to climate change. But the one that gets the most attention is its contribution via CO2 emissions. Most flights are powered by jet gasoline – although some partially run on biofuels – which is converted to CO2 when burned. In a recent paper, researchers – David Lee and colleagues – reconstructed annual CO2 emissions from global aviation dating back to 1940.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., ... & Gettelman, A. (2020). [The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018](https://www.sciencedirect.com/science/article/pii/S1352231020305689). _Atmospheric Environment_, 117834.{/ref} This was calculated based on fuel consumption data from the International Energy Agency (IEA), and earlier estimates from Robert Sausen and Ulrich Schumann (2000).{ref}Sausen, R., & Schumann, U. (2000). [Estimates of the climate response to aircraft CO2 and NOx emissions scenarios](https://link.springer.com/article/10.1023/A:1005579306109). _Climatic Change_, _44_(1-2), 27-58.{/ref} The time series of global emissions from aviation since 1940 is shown in the accompanying chart. In 2018, it’s estimated that global aviation – which includes both passenger and freight – emitted 1.04 billion tonnes of CO2. This represented 2.5% of [total CO2 emissions](https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels) in 2018.{ref}The Global Carbon Budget estimated total CO2 emissions from all fossil fuels, cement production and land-use change to be 42.1 billion tonnes in 2018. This means aviation accounted for [1 / 42.1 * 100] = 2.5% of total emissions.{/ref},{ref}Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project. [https://doi.org/10.18160/gcp-2019](https://doi.org/10.18160/gcp-2019). If we were to exclude land use change emissions, aviation accounted for 2.8% of fossil fuel emissions. The Global Carbon Budget estimated total CO2 emissions from fossil fuels and cement production to be 36.6 billion tonnes in 2018. This means aviation accounted for [1 / 36.6 * 100] = 2.8% of total emissions.{/ref} Aviation emissions have doubled since the mid-1980s. But, they’ve been growing at a similar rate as total CO2 emissions – this means its share of global emissions has been relatively stable: in the range of 2% to 2.5%.{ref}2.3% to 2.8% of emissions if land use is excluded.{/ref} <Image filename="Global-CO2-emissions-from-aviation.png" alt=""/> ## Non-CO2 climate impacts mean aviation accounts for 3.5% of global warming Aviation accounts for around 2.5% of global CO2 emissions, but it’s overall contribution to climate change is higher. This is because air travel does not only emit CO2: it affects the climate in a number of more complex ways. As well as emitting CO2 from burning fuel, planes affect the concentration of other gases and pollutants in the atmosphere. They result in a short-term increase, but long-term decrease in ozone (O3); a decrease in methane (CH4); emissions of water vapour; soot; sulfur aerosols; and water contrails. While some of these impacts result in warming, others induce a cooling effect. Overall, the warming effect is stronger. David Lee et al. (2020) quantified the overall effect of aviation on global warming when all of these impacts were included.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., ... & Gettelman, A. (2020). [The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018](https://www.sciencedirect.com/science/article/pii/S1352231020305689). _Atmospheric Environment_, 117834.{/ref} To do this they calculated the so-called ‘Radiative Forcing’. Radiative forcing measures the difference between incoming energy and the energy radiated back to space. If more energy is absorbed than radiated, the atmosphere becomes warmer. In their chart we see [their estimates for the radiative forcing](https://ars.els-cdn.com/content/image/1-s2.0-S1352231020305689-gr3_lrg.jpg) of the different elements. When we combine them, aviation accounts for approximately 3.5% of effective radiative forcing: that is, 3.5% of warming. Although CO2 gets most of the attention, it accounts for less than half of this warming. Two-thirds (66%) comes from non-CO2 forcings. Contrails – water vapor trails from aircraft exhausts – account for the largest share. ## We don’t yet have the technologies to decarbonize air travel Aviation’s contribution to climate change – 3.5% of warming, or 2.5% of CO2 emissions – is often less than people think. It’s currently a relatively small chunk of emissions compared to other sectors. The key challenge is that it is particularly hard to decarbonize. We have solutions to reduce emissions for many of the [largest emitters](https://ourworldindata.org/ghg-emissions-by-sector) – such as power or road transport – and it’s now a matter of scaling them. We can deploy renewable and nuclear energy technologies, and transition to electric cars. But we don’t have proven solutions to tackle aviation yet. There are some design concepts emerging – Airbus, for example, [have announced plans](https://web.archive.org/web/20201031121346/https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html) to have the first zero-emission aircraft by 2035, using hydrogen fuel cells. Electric planes may be a viable concept, but are likely to be limited to very small aircraft due to the limitations of battery technologies and capacity. Innovative solutions may be on the horizon, but they’re likely to be far in the distance. ### Towards zero-carbon transport: how can we expect the sector’s CO<sub>2</sub> emissions to change in the future? ourworldindata.org/co2-emissions-from-transport ## Additional information Global emissions from aviation have increased a lot over the past half-century. However, air travel volumes increased even more rapidly. Since 1960, aviation emissions increased almost seven-fold; since 1970 they’ve tripled. Air traffic volume – here defined as revenue passenger kilometers (RPK) traveled – [increased by orders of magnitude more](https://ourworldindata.org/grapher/airline-capacity-and-traffic): almost 300-fold since 1950; and 75-fold since 1960.{ref}Airline traffic data comes from the International Civil Aviation Organization (ICAO) via [Airlines for America](https://www.airlines.org/dataset/world-airlines-traffic-and-capacity). Revenue passenger kilometers (RPK) measures the number of paying passengers multiplied by their distance traveled.{/ref} The much slower growth in emissions means aviation efficiency has seen massive improvements. In the chart we show both the increase in global airline traffic since 1950, and aviation efficiency, measured as the quantity of CO2 emitted per revenue passenger kilometer traveled. In 2018, approximately 125 grams of CO2 were emitted per RPK. In 1960, this was eleven-fold higher; in 1950 it was twenty-fold higher. Aviation has seen massive efficiency improvements over the past 50 years. These improvements have come from several sources: improvements in the design and technology of aircraft; larger aircraft sizes (allowing for more passengers per flight); and an increase in how ‘full’ passenger flights are. This last metric is termed the ‘passenger load factor’. The passenger load factor measures the actual number of kilometers traveled by paying customers (RPK) as a percentage of the available seat kilometers (ASK) – the kilometers traveled if every plane was full. If every plane was full the passenger load factor would be 100%. If only three-quarters of the seats were filled, it would be 75%. The global passenger load factor [increased from 61% in 1950 to 82% in 2018](https://ourworldindata.org/grapher/airline-passenger-load-factor). <Image filename="Aviation-traffic-and-efficiency-Lee-et-al.-2020.png" alt=""/> | {
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"content": "\n<p>Flying is a highly controversial topic in climate debates. There are a few reasons for this. </p>\n\n\n\n<p>The first is the disconnect between its role in our personal and collective carbon emissions. Air travel dominates a frequent traveller’s individual contribution to climate change. Yet aviation overall accounts for only 2.5% of global carbon dioxide (CO<sub>2</sub>) emissions. This is because there are large inequalities in how much people fly \u2013 many do not, or cannot afford to, fly at all.{ref}The best estimates put this figure at around 80% of the world population. We look at this in more detail in our article “<a href=\"https://ourworldindata.org/carbon-footprint-flying\">Where in the world do people have the highest CO2 emissions from flying?</a>“{/ref}</p>\n\n\n\n<p>The second is how aviation emissions are attributed to countries. CO<sub>2</sub> emissions from domestic flights <em>are</em> counted in a country\u2019s emission accounts. International flights are not \u2013 instead they are counted as their own category: \u2018bunker fuels\u2019. The fact that they don\u2019t count towards the emissions of any country means there are few incentives for countries to reduce them.</p>\n\n\n\n<p>It\u2019s also important to note that unlike the most common greenhouse gases \u2013 carbon dioxide, methane or nitrous oxide \u2013 non-CO<sub>2</sub> forcings from aviation <em>are not included</em> in the Paris Agreement. This means they could be easily overlooked \u2013 especially since international aviation is not counted within any country\u2019s emissions inventories or targets.</p>\n\n\n\n<p>How much of a role does aviation play in global emissions and climate change? In this article we take a look at the key numbers that are useful to know.</p>\n\n\n\n<p>Global aviation (including domestic and international; passenger and freight) accounts for:</p>\n\n\n\n<ul><li><strong>1.9%</strong> of <a href=\"https://ourworldindata.org/ghg-emissions-by-sector\">greenhouse gas emissions</a> (which includes all greenhouse gases, not only CO<sub>2</sub>)</li><li><strong>2.5%</strong> of CO<sub>2</sub> emissions</li><li><strong>3.5%</strong> of ‘effective radiative forcing’ \u2013 a closer measure of its impact on warming.</li></ul>\n\n\n\n<p>The latter two numbers refer to 2018, and the first to 2016, the latest year for which such data are available.</p>\n\n\n\n<hr class=\"wp-block-separator\"/>\n\n\n\n<h4>Aviation accounts for 2.5% of global CO<sub>2</sub> emissions</h4>\n\n\n\n<p>As we will see later in this article, there are a number of processes by which aviation contributes to climate change. But the one that gets the most attention is its contribution via CO<sub>2</sub> emissions. Most flights are powered by jet gasoline \u2013 although some partially run on biofuels \u2013 which is converted to CO<sub>2</sub> when burned. </p>\n\n\n\n<p>In a recent paper, researchers \u2013 David Lee and colleagues \u2013 reconstructed annual CO<sub>2 </sub>emissions from global aviation dating back to 1940.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., … & Gettelman, A. (2020). <a href=\"https://www.sciencedirect.com/science/article/pii/S1352231020305689\">The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018</a>. <em>Atmospheric Environment</em>, 117834.{/ref} This was calculated based on fuel consumption data from the International Energy Agency (IEA), and earlier estimates from Robert Sausen and Ulrich Schumann (2000).{ref}Sausen, R., & Schumann, U. (2000). <a href=\"https://link.springer.com/article/10.1023/A:1005579306109\">Estimates of the climate response to aircraft CO2 and NOx emissions scenarios</a>. <em>Climatic Change</em>, <em>44</em>(1-2), 27-58.{/ref}</p>\n\n\n\n<p>The time series of global emissions from aviation since 1940 is shown in the accompanying chart. In 2018, it\u2019s estimated that global aviation \u2013 which includes both passenger and freight \u2013 emitted 1.04 billion tonnes of CO<sub>2</sub>.</p>\n\n\n\n<p>This represented 2.5% of <a href=\"https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels\" data-type=\"URL\" data-id=\"https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels\">total CO<sub>2</sub> emissions</a> in 2018.{ref}The Global Carbon Budget estimated total CO<sub>2</sub> emissions from all fossil fuels, cement production and land-use change to be 42.1 billion tonnes in 2018. This means aviation accounted for [1 / 42.1 * 100] = 2.5% of total emissions.{/ref}<sup>,</sup>{ref}Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project. <a href=\"https://doi.org/10.18160/gcp-2019\">https://doi.org/10.18160/gcp-2019</a>.<br><br>If we were to exclude land use change emissions, aviation accounted for 2.8% of fossil fuel emissions. The Global Carbon Budget estimated total CO<sub>2</sub> emissions from fossil fuels and cement production to be 36.6 billion tonnes in 2018. This means aviation accounted for [1 / 36.6 * 100] = 2.8% of total emissions.{/ref}</p>\n\n\n\n<p>Aviation emissions have doubled since the mid-1980s. But, they\u2019ve been growing at a similar rate as total CO<sub>2</sub> emissions \u2013 this means its share of global emissions has been relatively stable: in the range of 2% to 2.5%.{ref}2.3% to 2.8% of emissions if land use is excluded.{/ref}</p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" width=\"693\" height=\"550\" src=\"https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-693x550.png\" alt=\"\" class=\"wp-image-36836\" srcset=\"https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-693x550.png 693w, https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-400x318.png 400w, https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-150x119.png 150w, https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation-768x610.png 768w, https://owid.cloud/app/uploads/2020/10/Global-CO2-emissions-from-aviation.png 1505w\" sizes=\"(max-width: 693px) 100vw, 693px\" /></figure>\n\n\n\n<h4>Non-CO<sub>2</sub> climate impacts mean aviation accounts for 3.5% of global warming</h4>\n\n\n\n<p>Aviation accounts for around 2.5% of global CO<sub>2</sub> emissions, but it\u2019s overall contribution to climate change is higher. This is because air travel does not only emit CO<sub>2</sub>: it affects the climate in a number of more complex ways.</p>\n\n\n\n<p>As well as emitting CO<sub>2</sub> from burning fuel, planes affect the concentration of other gases and pollutants in the atmosphere. They result in a short-term increase, but long-term decrease in ozone (O<sub>3</sub>); a decrease in methane (CH<sub>4</sub>); emissions of water vapour; soot; sulfur aerosols; and water contrails. While some of these impacts result in warming, others induce a cooling effect. Overall, the warming effect is stronger.</p>\n\n\n\n<p>David Lee et al. (2020) quantified the overall effect of aviation on global warming when all of these impacts were included.{ref}Lee, D. S., Fahey, D. W., Skowron, A., Allen, M. R., Burkhardt, U., Chen, Q., … & Gettelman, A. (2020). <a href=\"https://www.sciencedirect.com/science/article/pii/S1352231020305689\">The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018</a>. <em>Atmospheric Environment</em>, 117834.{/ref} To do this they calculated the so-called \u2018Radiative Forcing\u2019. Radiative forcing measures the difference between incoming energy and the energy radiated back to space. If more energy is absorbed than radiated, the atmosphere becomes warmer. </p>\n\n\n\n<p>In their chart we see <a href=\"https://ars.els-cdn.com/content/image/1-s2.0-S1352231020305689-gr3_lrg.jpg\" target=\"_blank\" rel=\"noreferrer noopener\">their estimates for the radiative forcing</a> of the different elements. When we combine them, aviation accounts for approximately 3.5% of effective radiative forcing: that is, 3.5% of warming.<br><br>Although CO<sub>2 </sub>gets most of the attention, it accounts for less than half of this warming. Two-thirds (66%) comes from non-CO<sub>2 </sub>forcings. Contrails \u2013 water vapor trails from aircraft exhausts \u2013 account for the largest share.</p>\n\n\n\n<h4>We don\u2019t yet have the technologies to decarbonize air travel</h4>\n\n\n\n<p>Aviation\u2019s contribution to climate change \u2013 3.5% of warming, or 2.5% of CO<sub>2</sub> emissions \u2013 is often less than people think. It\u2019s currently a relatively small chunk of emissions compared to other sectors. </p>\n\n\n\n<p>The key challenge is that it is particularly hard to decarbonize. We have solutions to reduce emissions for many of the <a href=\"https://ourworldindata.org/ghg-emissions-by-sector\">largest emitters</a> \u2013 such as power or road transport \u2013 and it\u2019s now a matter of scaling them. We can deploy renewable and nuclear energy technologies, and transition to electric cars. But we don\u2019t have proven solutions to tackle aviation yet. </p>\n\n\n\n<p>There are some design concepts emerging \u2013 Airbus, for example, <a href=\"https://web.archive.org/web/20201031121346/https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html\" data-type=\"URL\" data-id=\"https://web.archive.org/web/20201031121346/https://www.airbus.com/innovation/zero-emission/hydrogen/zeroe.html\">have announced plans</a> to have the first zero-emission aircraft by 2035, using hydrogen fuel cells. Electric planes may be a viable concept, but are likely to be limited to very small aircraft due to the limitations of battery technologies and capacity. </p>\n\n\n\n<p>Innovative solutions may be on the horizon, but they\u2019re likely to be far in the distance.</p>\n\n\n <block type=\"prominent-link\" style=\"is-style-thin\">\n <link-url>http://ourworldindata.org/co2-emissions-from-transport</link-url>\n <title>Towards zero-carbon transport: how can we expect the sector\u2019s CO<sub>2</sub> emissions to change in the future?</title>\n <content>\n\n<p></p>\n\n</content>\n <figure><img width=\"768\" height=\"485\" src=\"https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-768x485.png\" class=\"attachment-medium_large size-medium_large\" alt=\"\" loading=\"lazy\" srcset=\"https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-768x485.png 768w, https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-400x253.png 400w, https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-800x505.png 800w, https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-150x95.png 150w, https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070-1536x970.png 1536w, https://owid.cloud/app/uploads/2020/10/IEA-Transport-to-2070.png 1732w\" sizes=\"(max-width: 768px) 100vw, 768px\" /></figure>\n </block>\n\n\t<block type=\"additional-information\" default-open=\"true\">\n\t\t<content>\n\n<h3>Appendix: <strong>Efficiency improvements means air traffic has increased more rapidly than emissions</strong></h3>\n\n\n\n<div class=\"wp-block-columns is-style-sticky-right\">\n<div class=\"wp-block-column\">\n<p>Global emissions from aviation have increased a lot over the past half-century. However, air travel volumes increased even more rapidly. </p>\n\n\n\n<p>Since 1960, aviation emissions increased almost seven-fold; since 1970 they\u2019ve tripled. Air traffic volume \u2013 here defined as revenue passenger kilometers (RPK) traveled \u2013 <a href=\"https://ourworldindata.org/grapher/airline-capacity-and-traffic\">increased by orders of magnitude more</a>: almost 300-fold since 1950; and 75-fold since 1960.{ref}Airline traffic data comes from the International Civil Aviation Organization (ICAO) via <a href=\"https://www.airlines.org/dataset/world-airlines-traffic-and-capacity\">Airlines for America</a>. Revenue passenger kilometers (RPK) measures the number of paying passengers multiplied by their distance traveled.{/ref}\u00a0</p>\n\n\n\n<p>The much slower growth in emissions means aviation efficiency has seen massive improvements. In the chart we show both the increase in global airline traffic since 1950, and aviation efficiency, measured as the quantity of CO<sub>2</sub> emitted per revenue passenger kilometer traveled. In 2018, approximately 125 grams of CO<sub>2 </sub> were emitted per RPK. In 1960, this was eleven-fold higher; in 1950 it was twenty-fold higher. Aviation has seen massive efficiency improvements over the past 50 years.</p>\n\n\n\n<p>These improvements have come from several sources: improvements in the design and technology of aircraft; larger aircraft sizes (allowing for more passengers per flight); and an increase in how \u2018full\u2019 passenger flights are. This last metric is termed the \u2018passenger load factor\u2019. The passenger load factor measures the actual number of kilometers traveled by paying customers (RPK) as a percentage of the available seat kilometers (ASK) \u2013 the kilometers traveled if every plane was full. If every plane was full the passenger load factor would be 100%. If only three-quarters of the seats were filled, it would be 75%.</p>\n\n\n\n<p>The global passenger load factor <a href=\"https://ourworldindata.org/grapher/airline-passenger-load-factor\">increased from 61% in 1950 to 82% in 2018</a>.\u00a0\u00a0</p>\n</div>\n\n\n\n<div class=\"wp-block-column\">\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" width=\"800\" height=\"505\" src=\"https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-800x505.png\" alt=\"\" class=\"wp-image-36837\" srcset=\"https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-800x505.png 800w, https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-400x253.png 400w, https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-150x95.png 150w, https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-768x485.png 768w, https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020-1536x970.png 1536w, https://owid.cloud/app/uploads/2020/10/Aviation-traffic-and-efficiency-Lee-et-al.-2020.png 1832w\" sizes=\"(max-width: 800px) 100vw, 800px\" /></figure>\n</div>\n</div>\n\n</content>\n\t</block>"
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