Volcanoes not our biggest polluter
Climate change isn’t all that difficult to understand. A British scientist proved shortly before the American civil war that carbon dioxide absorbs heat, and a Swedish chemist doodled out the first equations involving fossil-fuel emissions before the 20th century even began.
What was difficult to separate out, however, was identifying the human-driven signal within the noise of the vast, messy, and natural climate system. We know that what we burn ends up in the atmosphere, driving up the Earth’s planetary fever. At least at first it does.
What happens to CO2 after that? Sure, some of it can remain in the atmosphere for hundreds of years. But much of it – on average half of annual global emissions – leaves the atmosphere for greener pastures, literally, or for the ocean, which is ultimately the biosphere’s biggest carbon repository.
So what happens to all the carbon we burn after we burn it? How does it know where to go? A threeyear Nasa mission has given researchers a huge hand in tracking how CO2 pours out of industrial sources, in and out of land, seas, and the atmosphere. The net picture is a geologically abrupt flushing out, by burning and warming, of carbon that’s been trapped underground for up to many millions of years.
Nasa’s Orbiting Carbon Observatory-2 (OCO-2) is the subject of five studies in the journal Science published yesterday. They provide new details into these critical flows around the world: how shifting patterns in weather – altering tropical Pacific Ocean temperatures – can change the pace of the global CO2 rise; where CO2 travels after leaving specific sources, such as metropolitan Los Angeles or a volcano on Vanuatu; and how change in plant photosynthesis – now visible from space – is responding to the increasing amount of carbon that vegetation is sucking out of the air.
The satellite, launched in July 2014, may represent Nasa’s most nuanced instance of wordplay: ‘‘O=C=O’’ is itself a chemical diagram of the CO2 molecule, and the abbreviation of this ‘‘eye in the sky’’, OCO, is a homophone for the word ‘‘eye’’ in several languages.
The mission orbiting the Earth complements a global network of almost 150 greenhouse gas monitors on the ground which give scientists an ever-more detailed look at the atmosphere’s composition. OCO-3 will be fitted
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onto the International Space Station in the next few years, providing west-east measurements to complement OCO-2’s polar orbit. (OCO-1 was destroyed in a postlaunch accident.)
The instruments on OCO-2 analyse the atmosphere from an altitude of about 700 kilometres. The satellite’s tools, which were built to take kilometre-scale, sequential geographic snapshots, can also image specific features on the ground. One of the five studies analysed CO2 above a southern Pacific volcano and metropolitan Los Angeles.
Cities are responsible for more than 70 per cent of humanity’s CO2 emissions, but ground-based monitoring has been insufficient to provide targeted data. The satellite, however, not only discerns pollution differences between cities and rural areas, but those within cities as well – tools that may prove keenly useful to local policymakers trying to understand their own CO2 burden.
OCO-2 has also gone a long way towards dispelling a pervasive myth about carbon emissions – the one where climate change-deniers point to volcanoes as the key source of greenhouse gases rather than man. There are about 450 ‘‘passive’’ volcanoes around the world that continuously emit carbon dioxide, but there’s not enough funding to measure all of them from the ground. Having an orbiting monitor helps scientists predict eruptions and better understand the relationship between CO2 off-gassing and volcanic activity.
OCO-2 carbon-mapped the Yasur volcano in Vanuatu, and discovered that, by comparison, power plants in many cases are larger sources of CO2 than passive volcanoes.
‘‘The highest emitters [among] the volcanoes are equal or superseded by about 70 fossil fuel power plants on Earth,’’ says Florian Schwandner of the Jet Propulsion Laboratory, lead author of a paper on regional-monitoring of carbon emissions. ‘‘What that shows us is that volcanoes are likely not a significant source of CO2.’’
Volcanoes give off about 540 megatons of carbon dioxide a year, compared with up to 38,200 megatons from humanity. The study says that not only are large, persistent volcanoes outgunned by any of several dozen power plants, but those plants ‘‘themselves are dwarfed by megacity emissions’’.
The overall idea behind the research was to better understand how humanity is changing the Earth. Think of the planet as a flooding basement: scientists in charge of OCO-2 are trying to figure out where the water is coming from and flowing to. That information in turn could inform policymakers interested in stopping the leak in time.
About 25 per cent of human emissions is absorbed by land. Another 25 per cent is absorbed by the oceans, which as CO2 emissions have accelerated, is changing the chemical conditions there perhaps faster than at anytime in the last 300 million years.
The other half – on average – stays in the atmosphere. A longstanding mystery among Earth scientists is the different rates at which air, sea, and land absorb carbon dioxide. In the atmosphere, it’s been increasing at a steady, annual pace of about 2 parts CO2 for every million parts of air. But the amount that the sea and land sop up can vary from 20 per cent to 80 per cent in any particular year.
OCO-2’s scientific mission happened to coincide with the development of a monstrous El Nino, which dried out Australia, Central America, and the southern Amazon, while wreaking precipitative havoc elsewhere. Dryness means more carbon dioxide for the atmosphere – particularly when forests burn, as they did in Indonesia in 2015, and are doing in Northern California now.
As predicted at the time, a carbon gush in 2016 tipped the global atmosphere permanently above the symbolic threshold of 400 parts CO2 per million bits of air. What the researchers learned from OCO2 is that the gush, driven by El Nino, would have been even greater if the Pacific Ocean itself hadn’t absorbed more CO2 than usual.
As it stands, the variability helped push the rate of atmospheric CO2 growth that year 50 per cent higher, to about 3 ppm. It could have been much, much worse.
Abhishek Chatterjee, a research scientist at the University Space Research Association who’s stationed at the Nasa Goddard Space Flight Centre, is the lead author of one of the two El Nino papers in Science.
He put the role of the oceans quite simply, calling them ‘‘one of the largest sinks for released carbon dioxide’’. As industrial emissions continue and warming itself begins to squeeze CO2 from land and sea, OCO-2 and similar projects will help scientists better understand just how much room is left. – Washington Post