{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,27]],"date-time":"2026-07-27T22:13:47Z","timestamp":1785190427916,"version":"3.55.0"},"reference-count":124,"publisher":"Public Library of Science (PLoS)","issue":"8","license":[{"start":{"date-parts":[[2025,8,20]],"date-time":"2025-08-20T00:00:00Z","timestamp":1755648000000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS One"],"abstract":"<jats:p>Estimating and predicting CO<jats:sub>2<\/jats:sub> emissions are the keys to achieving the overall greenhouse gas emission goals for 2030 and 2050. Recent surges in space tourism have generated significant interest and concern. However, the associated CO<jats:sub>2<\/jats:sub> emission and potential future increase remain largely uncertain due to limited publicly available information from the industry. Focusing on suborbital flights, we develop an analytical model to estimate the associated CO<jats:sub>2<\/jats:sub> emissions, considering differences in spacecraft, fuel types, and flight characteristics. The model is based on basic physical principles and fundamental kinetics of the launching and landing phases. We find that suborbital tourism releases 400\u20131,000 times more CO<jats:sub>2<\/jats:sub> per passenger per hour compared with commercial aviation flights. The spacecraft using liquid hydrogen as fuel releases nearly the least amount of CO<jats:sub>2<\/jats:sub>; however, it is still associated with 90\u2013106 metric tons of indirect CO<jats:sub>2<\/jats:sub> emissions due to the fuel production process. In contrast, spacecraft using kerosene (RP-1) and solid fuel (HTPB), respectively, release significantly more. However, if methane (natural gas) is used as fuel, its emissions may become comparable with those using liquid hydrogen, but its maximum reduction in emission can only be less than 10% because that is the amount associated with production. Generally, conventional rocket fuels generate more CO<jats:sub>2<\/jats:sub> than emerging fuels such as hydrogen and methane. Even though the total emissions of suborbital flights are still small compared with commercial aviation, their emission intensity (i.e., per passenger per hour) is enormous (85\u2013226 tons vs. 250 kg). If the demand for suborbital flights increases significantly, as some have speculated, the total annual emission can be as large as 21 Mt CO<jats:sub>2<\/jats:sub> per year in a decade, which exceeds the annual emission of more than 100 countries. Even adopting a conservative estimate, CO<jats:sub>2<\/jats:sub> emissions for suborbital travel can grow to a similar size to that of Congo (with a population of nearly 100 million). Therefore, the CO<jats:sub>2<\/jats:sub> emission from emerging suborbital travel needs more attention in the future.<\/jats:p>","DOI":"10.1371\/journal.pone.0328456","type":"journal-article","created":{"date-parts":[[2025,8,20]],"date-time":"2025-08-20T17:36:22Z","timestamp":1755711382000},"page":"e0328456","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":3,"title":["Estimating CO2 emissions due to present and future suborbital space tourism industry"],"prefix":"10.1371","volume":"20","author":[{"given":"Angela M.","family":"Huang","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7173-7761","authenticated-orcid":true,"given":"Yangyang","family":"Xu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2025,8,20]]},"reference":[{"issue":"22","key":"pone.0328456.ref001","doi-asserted-by":"crossref","first-page":"10017","DOI":"10.3390\/su162210017","article-title":"A Review of Carbon Emission Reduction During the Operation Stage of Substations","volume":"16","author":"W Che","year":"2024","journal-title":"Sustainability"},{"issue":"51","key":"pone.0328456.ref002","article-title":"Assessing farmers\u2019 contribution to greenhouse gas emission and the impact of adopting climate-smart agriculture on mitigation","volume":"9","author":"MA Israel","year":"2020","journal-title":"Ecol Process"},{"key":"pone.0328456.ref003","doi-asserted-by":"crossref","first-page":"100106","DOI":"10.1016\/j.clrc.2023.100106","article-title":"Research on carbon emission standards of automobile industry in BRI participating countries","volume":"8","author":"P Zhang","year":"2023","journal-title":"Clean Responsib Consumpt"},{"issue":"5820","key":"pone.0328456.ref004","article-title":"Can the UK deliver zero carbon ready homes by 2050?","volume":"16","author":"L Warren","year":"2024","journal-title":"Sustainability"},{"issue":"2","key":"pone.0328456.ref005","first-page":"16","article-title":"Transportation is critical to reducing greenhouse gas emissions in the United States","volume":"10","author":"DL Bleviss","year":"2021","journal-title":"WIREs Ener Environ"},{"issue":"10","key":"pone.0328456.ref006","doi-asserted-by":"crossref","first-page":"1049","DOI":"10.1108\/MRR-11-2014-0262","article-title":"Reducing transportation greenhouse gas emissions with collaborative distribution- a case study","volume":"38","author":"N Danloup","year":"2015","journal-title":"Manag Res Rev"},{"issue":"1","key":"pone.0328456.ref007","doi-asserted-by":"crossref","first-page":"343","DOI":"10.5198\/jtlu.2018.1173","article-title":"Reducing greenhouse gas emissions from transportation and land use: Lessons from West Coast states","volume":"11","author":"R Lewis","year":"2018","journal-title":"J Transport Land Use"},{"issue":"25","key":"pone.0328456.ref008","doi-asserted-by":"crossref","first-page":"11","DOI":"10.1177\/0361198118755714","article-title":"Reducing transportation greenhouse gas emissions through the development of policies targeting high-emitting trips","volume":"2672","author":"R Tu","year":"2018","journal-title":"Transport Res Rec J Transport Res Board"},{"issue":"22","key":"pone.0328456.ref009","first-page":"3520","article-title":"Aviation and global climate change in the 21st century","volume":"43","author":"DS Lee","year":"2009","journal-title":"Atmos Environ (1994)"},{"key":"pone.0328456.ref010","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1016\/j.atmosenv.2014.12.043","article-title":"Variation of radiative forcings and global warming potentials from regional aviation NOx emissions","volume":"104","author":"A Skowron","year":"2015","journal-title":"Atmosph Environ"},{"key":"pone.0328456.ref011","volume-title":"The growth in greenhouse gas emissions from commercial aviation","author":"J Overton","year":"2022"},{"key":"pone.0328456.ref012","volume-title":"IPCC Special Report Aviation and the Global Atmosphere - Summary for Policymakers","author":"JE Penner","year":"2000"},{"key":"pone.0328456.ref013","volume-title":"CO2 Emissions from Commercial Aviation","author":"B Graver","year":"2020"},{"key":"pone.0328456.ref014","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.jtrangeo.2014.08.004","article-title":"Greenhouse gas emissions from flying can offset the gain from reduced driving in dense urban areas","volume":"41","author":"J Ottelin","year":"2014","journal-title":"J Trans Geograp"},{"key":"pone.0328456.ref015","volume-title":"High Flyers 2023 - How Ultra-Rich Private Jet Travel Costs the Rest of Us and Burns Up Our Planet","author":"C Collins","year":"2023"},{"key":"pone.0328456.ref016","article-title":"Private jet travel is booming. 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