It is a faint silver lining to a year of COVID-19 lockdowns, and a distraction from the longer-term trend \u2013 in 2019, CO2<\/sub><\/span> emissions hit a record high (36.8bn tonnes). Now, as restrictions ease thanks to vaccination programmes, CO2<\/sub><\/span> emissions are returning to pre-pandemic levels.<\/p>\n After taking office in January 2021, President Joe Biden reinstated America\u2019s commitment to the Paris Agreement, an international treaty on climate change.<\/p>\n Read more:<\/strong><\/em><\/p>\n In April, British Prime Minister Boris Johnson set new, more aggressive emissions reduction targets for the UK.<\/p>\n In May, Germany brought its deadline to become carbon neutral forward to 2045.<\/p>\n And further pledges to cut CO2<\/sub><\/span> may come in November 2021\u2019s UN Climate Change Conference of the Parties (COP26).<\/p>\n But such pledges are meaningless unless action is taken to keep them. And how will we know if those actions are having an effect?<\/p>\n More to the point, how do we know how much CO2<\/sub><\/span> there is in the atmosphere to begin with?<\/p>\n Scientists, such as Dr Annmarie Eldering, can answer those questions with the help of CO2<\/sub><\/span>-monitoring satellites.<\/p>\n Eldering has been involved in the task since NASA\u2019s Orbiting Carbon Observatory<\/a>-2 (OCO-2) got the go-ahead in February 2010.<\/p>\n She had joined NASA\u2019s Jet Propulsion Lab in the late 1990s to work on measuring air pollution from space.<\/p>\n \u201cIt was a pretty small leap to go from air pollution to measuring CO2<\/sub><\/span>,\u201d she says.<\/p>\n \u201cCO2<\/sub><\/span> is the most important of the gases humans emit for driving climate change. It\u2019s a really big problem, for us and the globe.<\/p>\n \u201cIt\u2019s something we\u2019ve got to understand and start acting on. But measuring CO2<\/sub><\/span> from space is challenging.\u201d<\/p>\n Challenging is an understatement. Since 2016, the concentration of CO2<\/sub><\/span> in the atmosphere has been over 400 parts per million \u2013 a level unseen since the mid-Pliocene, 3 million years ago.<\/p>\n But as high as that is, it\u2019s still a staggeringly difficult amount to keep track of. Imagine trying to account for 400 pennies scattered among one million coins of all denominations spread across a floor.<\/p>\n Now imagine that each day someone adds a few more pennies or takes a couple away. That\u2019s the challenge Eldering and the OCO-2 team took on.<\/p>\n They weren\u2019t starting from scratch, though. Thanks to Eunice Foote and John Tyndall\u2019s work in the 1850s, we know about the dangers of increasing concentrations of atmospheric CO2<\/sub><\/span>, a greenhouse gas, on the climate.<\/p>\n And since Charles David Keeling established a weather station on Hawaii\u2019s Mauna Loa volcano in 1958, we\u2019ve been monitoring them.<\/p>\n But the Mauna Loa Observatory only gives us a tiny snapshot of the CO2<\/sub><\/span> in Earth\u2019s atmosphere.<\/p>\n Even the global network of ground- and sea-based monitoring stations that has developed to support it can\u2019t provide a complete picture.<\/p>\n And that\u2019s because Earth\u2019s atmosphere extends to around 10,000m above sea level, so most of it is nowhere near the monitoring equipment. Hence the need for CO2<\/sub><\/span>-monitoring satellites.<\/p>\n \u201cThe big motivation was to find out, on a global scale, how CO2<\/sub><\/span> moves between the atmosphere, the ocean and the land,\u201d says Eldering.<\/p>\n \u201cAs a lot of our information came from ground- and ship-based measurements, there was a huge part of Earth we didn\u2019t observe.\u201d<\/p>\n OCO-2 launched on 2 July 2014 and OCO-3 on 4 May 2019. Together, they help to keep track of the CO2<\/sub><\/span> in Earth\u2019s atmosphere.<\/p>\n Fundamentally, they\u2019re the same \u2013 both carry an instrument containing spectrometers that measure wavelengths of sunlight that have reflected off Earth\u2019s surface and passed through the atmosphere.<\/p>\n \u201cWhat\u2019s important about that is every gas [in the atmosphere] has a unique way of interacting with light,\u201d says Eldering.<\/p>\n \u201c[Each gas] absorbs a little bit of light as it passes through. So if you know the pattern of absorption for a particular gas and you\u2019ve got a really precise measurement of the light; you can see that there were more molecules [of that gas] here than there were over there.\u201d<\/p>\n With that information, scientists can see where CO2<\/sub><\/span> is accumulating and how it\u2019s influenced by temperature and pressure changes, climatic or geological events (such as El Ni\u00f1o events or volcanic eruptions), and even seasonal vegetation growth.<\/p>\n Where OCO-2 and OCO-3 differ is in what their instruments are attached to.<\/p>\n OCO-2\u2019s is packaged into a satellite in heliosynchronous orbit; OCO-3\u2019s is mounted on the International Space Station<\/a> (ISS).<\/p>\n What that means is OCO-2 orbits the poles at an altitude of 700km, passing over any given spot at the same time (guaranteeing it\u2019s in sunlight).<\/p>\n Meanwhile, OCO-3 orbits with the ISS, about 400km above Earth, and sees different locations at different times.<\/p>\n There has always been, and always should be, some CO2<\/sub><\/span> in Earth\u2019s atmosphere because every living thing emits CO2<\/sub><\/span>, either through respiration while it\u2019s alive or decomposition once it\u2019s dead.<\/p>\n But those emissions are balanced by the CO2<\/sub><\/span> absorbed by photosynthesis and colder parts of the oceans.<\/p>\n The problem is that CO2<\/sub><\/span> emissions from human activity \u2013 anthropogenic emissions \u2013 have unbalanced that natural cycle.<\/p>\n Ever since we began burning fossil fuels (oil, coal and natural gas) we\u2019ve essentially been digging up CO2<\/sub><\/span> that had been removed from the cycle and pumping it into the atmosphere.<\/p>\n But we\u2019ve failed to balance those emissions by creating new sinks to absorb that extra CO2<\/sub><\/span>.<\/p>\n To make matters worse, by clearing vast areas of rainforest across the tropics, we\u2019ve also decreased the capacity of Earth\u2019s natural CO2<\/sub><\/span> sinks, leaving us staring down the barrel of catastrophe.<\/p>\n Without taking action to reduce our CO2<\/sub><\/span> emissions, we\u2019re facing climate disaster.<\/p>\n The trouble is, we can\u2019t tell if those actions are helping without knowing how much CO2<\/sub><\/span> we\u2019re responsible for.<\/p>\n We need to differentiate between natural and anthropogenic CO2<\/sub><\/span>, and that\u2019s even harder than monitoring CO2<\/sub><\/span> from space.<\/p>\n To return to the coin analogy, it\u2019s akin to determining how many of those 400 pennies are real and how many are counterfeit.<\/p>\n It\u2019s difficult, but not impossible, provided you have a device that can measure nitrogen dioxide (NO2<\/sub><\/span>) levels.<\/p>\n![\""Joe\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2021\/09\/GettyImages-1297995990-9da3df4.jpg?quality=90&resize=620%2C414"\" "\\"\"Joe\\"")
<\/div>Why monitor climate change from space?<\/strong><\/h1>\n
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<\/div>What do climate-monitoring satellites do?<\/strong><\/h1>\n
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<\/div>Why is\u00a0 CO2 <\/sub><\/span>in Earth\u2019s atmosphere bad?<\/strong><\/h1>\n
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<\/div>\n![\""Illustration\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2021\/09\/08_Grace_FO_still_Above_Alaska-c73f7f0.jpg?quality=90&resize=620%2C349"\" "\\"\"GRACE-FO\"\\"")
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