By Daniel Grossman
Millions of stacks and tailpipes in cities around the world send up 70 percent of the carbon dioxide ejected into the atmosphere by human beings. And in the parts of the world, including the U.S., where many governments at all levels have offered only anemic or counterproductive responses to the climate crisis, officials in some cities are acting. Four hundred and sixty one mayors, including those of some of the U.S.'s largest cities, have joined Climate Mayors. They're pledging to uphold the goals of the 2015 Paris Climate Agreement, regardless of whether the U.S. remains in or bolts from that pact.
How can leaders choose carbon-cutting policies with the most impact? And how can they check to see if they're getting it right?
This past summer, Lucy Hutyra, a climate scientist at Boston University who studies urban fossil fuel use, invited me to see her latest research on tracking carbon dioxide emissions.
I bicycled over to BU Beach, an oasis of green on the highly urban university campus. Above her, Barry Logan, her colleague, balanced on a step ladder poked into the canopy of a linden tree. He pressed single serrated leaves against a soda-straw-thin metal tube, its tip sharpened like a leather punch. He shook a green plug of vegetation out of the tool and folded it inside a thumbnail of tinfoil. Hopping down from the ladder, he dropped the Lilliputian sample into a fuming tank of liquid nitrogen, 320 degrees Fahrenheit below zero.
Along with Logan, a plant physiologist, two other researchers had come along with Hutyra on that blistering August day. They sampled several trees in the park. They'd swathed in bubble wrap and strapped a device that measures sap flow to the trunk of a mature tree. And they'd deployed a little humor in the hopes of deterring would-be vandals. "Please wood you leaf the research alone," implored a sign on the tree.
Daniel Grossman
Hutyra's research is part of a wide-ranging campaign to improve estimates of fossil fuel emissions exhaled from the world's cities measured through time. By coincidence, Boston Mayor Marty Walsh, whose office is a few miles east of BU Beach, co-chairs Climate Mayors. His administration has made an ambitious commitment to make Boston carbon neutral by 2050. Hutyra's research could help Boston, and any other city, determine if it has succeeded. The political commitments produce physical results, she said. "If you have the state and city governments making pledges to reach carbon neutrality, it should be actualized in the atmosphere." Then she added with a smile, "and we can measure that."
Precise Sensor Atop Boston Skyscraper Gets CO2 Readings Each Minute
Steven Wofsy, a Harvard atmospheric scientist, is collaborating with Hutyra to hone a technique to make such measurements. Boston is also a test bed for him. He takes air samples 700 feet above the downtown's swankiest shopping district.
In 2012, Wofsy installed a precision gas sensor atop one of Boston's tallest skyscrapers, near Copley Square in downtown. It has since recorded the amount of carbon dioxide in the air, once each minute. He put five such detectors in a network, three on the far edge of the metro area, sampling background levels, to the north, south, and west.
Wofsy has hired a colleague's former grad student, Maryann Sargent, to perfect a method for tracking urban fossil fuel using his sensors' measurements. She simulates carbon dioxide flowing through the city's skies by conducting a virtual experiment. She hypothesizes that at some specific time and day, 1,000 infinitesimal parcels of air drift into the downtown detector. Call that time zero. Then, in the simulated place that she calls "model world," Sargent turns the clock backward one minute from the start of the experiment. Using actual wind records, she calculates where the parcels were from at that earlier time. And she determines how much carbon dioxide they must have borne then.
Like an Agatha Christie sleuth who has discovered a body, a murder weapon and a trainload of suspects, Sargent begins her work with the end result and a cast of the characters. One step at a time, to "solve the crime," she figures out how they converged in the final act. It's the only way for her to learn where the downtown air came from and what happened to it along the way.
Moving backward in time, Sargent computes how the carbon dioxide content of each air parcel changes in each minute of its reverse travels across the city. In this topsy-turvy, Alice-in-Wonderland scenario, fossil-fuel burning gradually removes carbon dioxide from the parcels. With the time in repeat, plants, which we normally think of as removing carbon dioxide, add it. Sargent uses two inventories of data that Hutyra has created, one tabulating carbon dioxide emissions from Boston's smokestacks and tailpipes, the other cataloging uptake of carbon dioxide by the city's vegetation.
Scraping information from databases such as cell phone logs – which record vehicle travel – and utility records – which show building energy use – Hutyra has computed hour-by-hour estimates of emissions within each cell of an imaginary grid of one-kilometer squares overlaying the Boston area. She's totaled estimates of the exhaust from every building, vehicle and, of course, electricity generating station within every cell.
In the other inventory, Hutyra has tallied plant uptake within each grid cell each hour of daylight (plants don't perform photosynthesis and take up carbon dioxide at night). Trees cover 27% of Boston's surface. The percentage increases in the verdant suburbs. Sargent says the databases clearly show that at times urban vegetation substantially reduces the amount of carbon dioxide added to the city's air. On some sunny days in some parts of Boston, plants take up more carbon than is added by fossil fuels. It would be pointless to simulate carbon dioxide concentrations in a verdant city like Boston, she says, without factoring in plants.
Sampling a Linden Tree ‘Not Behaving Like a Textbook Tree’
The day I visited BU Beach, Hutyra was refining her techniques for compiling plant uptake inventories. Among past findings, she has discovered that urban trees absorb twice as much carbon dioxide as the same size trees in a forest, a discovery with serious implications for her calculations. "This tree is not behaving like a textbook tree," she said, patting the linden they'd sampled. Compared to their forest counterparts, such urban trees get pampered with fertilizer and water.
From a nearby building they'd aimed a specialized camera that helps estimate a plant's carbon uptake. Logan took his leaf samples, frozen to the point of suspended animation, back to his lab, to compare tried-and-true laboratory methods for gauging leaf absorption of carbon dioxide with data from the newly-devised camera. He says that with more testing, carbon uptake by urban forests might someday be monitored with similar cameras circling on satellites.
Sargent rewinds time backwards in model world, minute by minute, carrying those imaginary parcels in an expanding cloud ever back in time and upwind. For each increment, she computes the amount of carbon dioxide each parcel exchanged with the surface, through the effects of fossil fuel use or plant growth. In time – three to twelve hours depending on wind speed – the imaginary cloud of parcels exits the metro area and passes by the location of one of Wofsy's rural detectors (which one depends on the wind direction of the simulated day). This is where the model-world experiment ends, a place where the carbon dioxide concentration is largely unaffected by the city.
From Military Intelligence to Climate Intelligence
In a 2018 paper in the Proceedings of the National Academy of Sciences Sargent, Hutyra, Wofsy and eight coauthors compared how much carbon dioxide those simulated air parcels lose moving backwards from downtown to the city's edge (or, equivalently, the difference in carbon dioxide concentration between the two places) with actual measurements from Wofsy's sensors. The simulated and actual numbers produced by the two methods were almost identical, within 14% of each other. Wofsy says the agreement between the figures proves that the model world closely resembles the real world, showing "our methods are not crazy."
With these methods, Sargent says, researchers can soon chart urban emission trends anywhere, even absent the painstaking inventories Hutyra tabulated for Boston, with no further boots on the ground: Orbiting carbon dioxide sensors combined with satellite photos will give them what they need.
In the near future when some country claims a city has made emissions reductions to meet obligations under the Paris Climate Agreement, researchers will be able to investigate the assertion, even if they aren't given data to justify it. Orbiting sensors, once intended for military intelligence alone, will now empower our climate intelligence. With satellite measurements of carbon dioxide concentrations and urban greenery across the city, and with images showing where people live, and the highways network and locations where electricity is generated, regulators could make a crude simulation of how the concentration of carbon dioxide changes across the city, just as Sargent did in Boston … and verify how much carbon dioxide was emitted there.
If satellite readings of the carbon dioxide concentrations they see don't line up with the claimed emissions reductions, a closer look might be worthwhile. As climate scientists like to say, the atmosphere doesn't lie.
Reposted with permission from Yale Climate Connections.
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Though made in large part of plastic, glass, ceramics, gold and copper, they also contain critical resources. The gallium used for LEDs and the camera flash, the tantalum in capacitors and indium that powers the display were all pulled from the ground — at a price for nature and people.
"Mining raw materials is always problematic, both with regard to human rights and ecology," said Melanie Müller, raw materials expert of the German think tank SWP. "Their production process is pretty toxic."
The gallium and indium in many phones comes from China or South Korea, the tantalum from the Democratic Republic of Congo or Rwanda. All in, such materials comprise less than ten grams of a phone's weight. But these grams finance an international mining industry that causes radioactive earth dumps, poisoned groundwater and Indigenous population displacement.
Environmental Damage: 'Nature Has Been Overexploited'
The problem is that modern technologies don't work without what are known as critical raw materials. Collectively, solar panels, drones, 3D printers and smartphone contain as many as 30 of these different elements sourced from around the globe. A prime example is lithium from Chile, which is essential in the manufacture of batteries for electric vehicles.
"No one, not even within the industry, would deny that mining lithium causes enormous environmental damage," Müller explained, in reference to the artificial lakes companies create when flushing the metal out of underground brine reservoirs. "The process uses vast amounts of water, so you end up with these huge flooded areas where the lithium settles."
This means of extraction results in the destruction and contamination of the natural water system. Unique plants and animals lose access to groundwater and watering holes. There have also been reports of freshwater becoming salinated due to extensive acidic waste water during lithium mining.
But lithium is not the only raw material that causes damage. Securing just one ton of rare earth elements produces 2,000 tons of toxic waste, and has devastated large regions of China, said Günther Hilpert, head of the Asia Research Division of the German think tank SWP.
He says companies there have adopted a process of spraying acid over the mining areas in order to separate the rare earths from other ores, and that mined areas are often abandoned after excavation.
"They are no longer viable for agricultural use," Hilpert said. "Nature has been overexploited."
China is not the only country with low environmental mining standards and poor resource governance. In Madagascar, for example, a thriving illegal gem and metal mining sector has been linked to rainforest depletion and destruction of natural lemur habitats.
States like Madagascar, Rwanda and the DRC score poorly on the Environmental Performance Index that ranks 180 countries for their effort on factors including conservation, air quality, waste management and emissions. Environmentalists are therefore particularly concerned that these countries are mining highly toxic materials like beryllium, tantalum and cobalt.
But it is not only nature that suffers from the extraction of high-demand critical raw materials.
"It is a dirty, toxic, partly radioactive industry," Hilpert said. "China, for example, has never really cared about human rights when it comes to achieving production targets."
Dirty, Toxic, Radioactive: Working in the Mining Sector
One of the most extreme examples is Baotou, a Chinese city in Inner Mongolia, where rare earth mining poisoned surrounding farms and nearby villages, causing thousands of people to leave the area.
In 2012, The Guardian described a toxic lake created in conjunction with rare earth mining as "a murky expanse of water, in which no fish or algae can survive. The shore is coated with a black crust, so thick you can walk on it. Into this huge, 10 sq km tailings pond nearby factories discharge water loaded with chemicals used to process the 17 most sought after minerals in the world."
Local residents reported health issues including aching legs, diabetes, osteoporosis and chest problems, The Guardian wrote.
South Africa has also been held up for turning a blind eye to the health impacts of mining.
"The platinum sector in South Africa has been criticized for performing very poorly on human rights — even within the raw materials sector," Müller said.
In 2012, security forces killed 34 miners who had been protesting poor working conditions and low wages at a mine owned by the British company Lonmin. What became known as the "Marikana massacre" triggered several spontaneous strikes across the country's mining sector.
Müller says miners can still face exposure to acid drainage — a frequent byproduct of platinum mining — that can cause chemical burns and severe lung damage. Though this can be prevented by a careful waste system.
Some progress was made in 2016 when the South African government announced plans to make mining companies pay $800 million (€679 million) for recycling acid mine water. But they didn't all comply. In 2020, activists sued Australian-owned mining company Mintails and the government to cover the cost of environmental cleanup.
Another massive issue around mining is water consumption. Since the extraction of critical raw materials is very water intensive, drought prone countries such as South Africa, have witnessed an increase in conflicts over supply.
For years, industry, government and the South African public debated – without a clear agreement – whether companies should get privileged access to water and how much the population may suffer from shortages.
Mining in Brazil: Replacing Nature, People, Land Rights
Beyond the direct health and environmental impact of mining toxic substances, quarrying critical raw materials destroys livelihoods, as developments in Brazil demonstrate.
"Brazil is the major worldwide niobium producer and reserves in [the state of] Minas Gerais would last more than 200 years [at the current rate of demand]," said Juliana Siqueira-Gay, environmental engineer and Ph.D. student at the University of São Paulo.
While the overall number of niobium mining requests is stagnating, the share of claims for Indigenous land has skyrocketed from 3 to 36 percent within one year. If granted, 23 percent of the Amazon forest and the homeland of 222 Indigenous groups could fall victim to deforestation in the name of mining, a study by Siqueira-Gay finds.
In early 2020, Brazilian President Jair Bolsonaro signed a bill which would allow corporations to develop areas populated by Indigenous communities in the future. The law has not yet entered into force, but "this policy could have long-lasting negative effects on Brazil's socio-biodiversity," said Siqueira-Gay.
One example are the niobium reserves in Seis Lagos, in Brazil's northeast, which could be quarried to build electrolytic capacitors for smartphones.
"They overlap the Balaio Indigenous land and it would cause major impacts in Indigenous communities by clearing forests responsible for providing food, raw materials and regulating the local climate," Siqueira-Gay explained.
She says scientific good practice guidelines offer a blueprint for sustainable mining that adheres to human rights and protects forests. Quarries in South America — and especially Brazil — funded by multilaterial banks like the International Finance Corporation of the World Bank Group have to follow these guidelines, Siqueira-Gay said.
They force companies to develop sustainable water supply, minimize acid exposure and re-vegetate mined surfaces. "First, negative impacts must be avoided, then minimized and at last compensated — not the other way around."
Reposted with permission from DW.