Why is Methane Such a Powerful Greenhouse Gas?

Why a little bit of methane goes a long way in warming the planet

We need to talk about methane.

According to two recent studies, global methane levels are at an all-time high.

This is a problem because over 20 years, methane is 86 times as potent a greenhouse gas as carbon dioxide, meaning 1 tonne of methane absorbs as much heat over 20 years as 86 tonnes of carbon dioxide.

For context, this graph displays the concentration of methane in the atmosphere over the past 1000 years. Just like our carbon dioxide levels, methane levels are rising fast.

Meanwhile, the Trump Administration rolled back regulations requiring oil and gas companies to detect and seal methane leaks. This is a considerable setback as the US energy and agriculture industries are tied as the top two sources of domestic methane emissions.

One of the studies on global methane levels has a chart showing the largest sources of methane. Taken together, human activities now produce more methane than natural sources.

(The accompanying table has a detailed breakup and points out some interesting facts. For example, I had no idea that rice cultivation is a large source of methane emissions, or that termites produce so much methane.)

A Hidden Puzzle

But there’s a science question lurking here. What makes methane such a powerful greenhouse gas compared to carbon dioxide? Why do some greenhouse gases pack more of a global warming punch compared to others?

Scientists call a greenhouse gas’s power to warm the planet its global warming potential. And topping this list are greenhouse gases you might never have heard of (with names like carbon tetrafluoride or sulfur hexafluoride).

Pound for pound, these gases are many thousands of times more effective at warming the planet than carbon dioxide. Why?

The answer is surprisingly counter-intuitive: dilute greenhouse gases pack a larger global-warming punch. To see why, we need to view the world from the perspective of a beam of light.

Why A Little Bit Goes a Long Way

Earth receives energy from the Sun mainly in the form of visible light. The planet absorbs and then emits this energy into space via invisible infrared light (i.e. radiated heat). Greenhouse gases block some of this escaping infrared light, thereby trapping heat and warming the planet.

Just as there are different colors of visible light, there are different wavelengths of infrared light. One set of infrared light wavelengths are blocked by carbon dioxide. Another set of infrared wavelengths are blocked by water vapor. Yet another set of wavelengths are blocked by methane. Each greenhouse gas blocks different ‘colors’ of infrared light.

So picture a beam of infrared light trying to escape the Earth. The atmosphere extends for dozens of miles, so this beam of light has a long way to go.

Now let’s sprinkle in a greenhouse gas that can block this beam of light. If the concentration of the greenhouse gas is very, very low, it’s unlikely that the beam will encounter a greenhouse gas molecule.

As the air gets crowded with more molecules of this gas, it’s increasingly likely that the beam of light will hit one of them. This light beam ends up ricocheting back and forth like a ball in a pinball machine, and its trapped energy warms the Earth.

If you were to graph the chance of a collision versus the concentration of the greenhouse gas, it’d look something like this.

Initially, when the gas is very dilute, for every step up in concentration, there’s a steep rise in the odds of bumping into a molecule.

But as the gas becomes more abundant, collisions become very likely, and so the same increase in concentration now results in a small rise in the chance of a collision.

It’s a lot like how when you add a few drops of ink in water, the water quickly becomes murky. But with enough drops of ink, the water becomes almost opaque, and you get diminishing returns from every added drop.

Image: jandrese, Fountain Pen Network. Notice that initially, small changes in ink dilution result in a large change in opacity. So every successive drop of ink blocks less and less light.

Just as every successive drop of ink blocks less and less light, every additional amount of greenhouse gas blocks a little less of Earth’s escaping heat — you get diminishing returns on global warming.

Which means the most dilute greenhouse gases pack the largest global-warming punch. That’s because at low concentrations, it’s easier to make the atmosphere ‘murky’ with greenhouse gas. At high concentrations, the air becomes saturated with the greenhouse gas, and so it’s harder to make a noticeable change in ‘murkiness’.

Note: This does *not* mean that Earth will become insensitive to adding more CO2. Adding more of a greenhouse gas always makes it warmer, it just does so in increasingly smaller steps.

Although this simple model brushes over the messy complexities of heat absorption, it offers a valuable insight, known to climate scientists as the band saturation effect.

Methane is a powerful greenhouse gas mainly because it’s at a low concentration. While the concentration of CO2 in the atmosphere is well over 400 parts per million, the concentration of methane is currently under 2 parts per million.

Because of this difference in concentration, methane makes the atmosphere ‘murkier’ than carbon dioxide does (when seen from the perspective of escaping infrared light). And that’s why methane takes a bigger bite out of our escaping heat.

So when it comes to greenhouse gases, a little bit goes a long way. This is why we need to be especially careful about trace greenhouse gases like methane as well as the hydrofluorocarbons (HFCs) released by ACs and fridges.

Most of these fluorocarbons didn’t exist before humans synthesized them, so their concentration started from zero, which is precisely why they have such an outsized warming effect.

In a way, this can be viewed optimistically — if low concentrations of gas have an outsized effect on warming, it also means that we can have an outsized effect on curtailing global warming by reducing our emissions of trace greenhouse gases like methane and fluorocarbons.

For example, the climate solutions website Project Drawdown considers developing newer air-conditioning and refrigeration technologies as among the most impactful ways to take a bite out of global greenhouse emissions.

References

If you’re interested in learning more about the science of the greenhouse effect, check out our three part explainer. I also recommend David Archer’s lectures and accompanying textbook. This science in this post is based on his lecture on The Band Saturation Effect.


The Rate of Change takes an accessible look at the science of climate change. If you’re reading this online, you can subscribe to this newsletter below.

If you value these in-depth science explainers, please consider supporting my writing on Patreon. And thanks for reading!

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Visualizing Greenland's Melting Ice

No Olympic-Sized Swimming Pools Were Harmed in the Writing of This Post

According to a new study, the Greenland ice sheet lost a record-breaking (and intuition-defying) 532 billion tonnes worth of ice in 2019. The Greenland ice sheet refers to the ice covering Greenland, which makes up the second largest body of ice in the world after the Antarctic ice sheet.

As I mentioned in the previous newsletter, Greenland’s melting ice is a Big Deal because it’s the single largest contributor to rising sea level. 2019’s melt alone is sufficient to raise global sea levels by 1.5 millimeters, enough water to hypothetically cover the state of California to a depth of 4 feet.

As climate scientist Andy Shephard told BBC News, “If Greenland's ice losses continue on their current trajectory, an extra 25 million people could be flooded each year by the end of this century.”(If all the ice in the Greenland ice sheet were to melt, it would raise global sea levels by about 7 meters, or 24 feet, although this would take centuries to occur.)

The ice is lost mainly through melting on the surface, as well as through ice at the edge of the sheet either falling into the ocean or melting underwater. Since the early 2000s, NASA satellites have made detailed measurements of Earth’s gravitational field, which allows scientists to effectively weigh different parts of the Earth.

The graph above shows last year in the context of the past two decades of ice loss. The vertical axis shows Greenland’s lost mass in billions of tonnes. Each year there’s a large drop in summer, followed by a small recovery in winter as snowfall accumulates.

Because the summer ice loss exceeds the ice gained from winter snowfall, we end up with this staircase-like graph. The drop in 2019 was larger than any preceding it, and the rate of melting is accelerating.

Lately the steps in this staircase have been getting larger, as Arctic temperatures have risen by nearly twice as much as global temperatures have in the past century. And climate models project that Arctic temperatures will rise two and a half times faster than temperatures at the tropics, so we can expect this trend to continue at least as long as our carbon emissions do.


Making Sense of Giant Numbers: A Guide for the Perplexed

But what does 532 billion tonnes of ice even mean? We might never be able to fully grasp numbers this large, but that doesn’t stop us from trying.

And it’s important that we make the effort, because climate science is all about planetary-scale forces that stretch our intuition. To understand the scale of these forces, we need to develop our intuition for large numbers.

So in this post I’m going to walk you through how I wrap my head around large numbers, and give you some pointers to help you make sense of these gigantic numbers yourself.

Strategy 1: Convert Unfamiliar Units Into Familiar Ones

This is a good problem-solving strategy in general — when faced with something you don’t understand, try to connect it to things you do understand.

Greenland lost 532 Gigatonnes (Gt for short) of ice in 2019. Theoretically, I know what a ‘Gigatonne’ is. A tonne is a thousand kilograms, and giga means a billion, so a Gigatonne is a thousand billion, i.e. a trillion kilograms.

But I have no intuition for how big that is. Instead, here’s something I do have an intuition for: 1 cubic meter. That’s just a box 1 meter long, 1 meter wide, 1 meter tall. You could build one yourself from PVC pipe (have I mentioned my enduring fondness for PVC pipe?) Or you could build one out of meter sticks, like this group of math teachers did.

So let’s convert the unfamiliar unit — 532 Gigatonnes of ice — into the familiar unit of cubic meters (m³). To convert a mass (kg) of ice into a volume (m³), we need to know the density of ice. Wikipedia tells me this is 917 kg/m³.

As a check, I happen to know that the density of water is 1000 kg/m³ (i.e., a cubic meter of water weighs a tonne). If you look at an ice cube floating in a glass of water, you’ll notice that roughly 90 percent of the ice is submerged. This teaches us that the density of ice should be ~90% the density of water, so the number above checks out. (Mini-tip: whenever possible, do a quick intuition check. It’ll pay off in the long run.)

Back to Greenland’s lost ice. If we divide the ice’s mass by its density, we’re left with its volume.

So Greenland lost 580 billion cubic meters of ice in 2019.

This is progress, although it might not seem like it. I might understand what 1 cubic meter looks like, but I certainly don’t have an intuition for billions of cubic meters.

Strategy 2: Tap Into your Geographical Intuition

Let’s work with what we’ve got. I live in New York City, so I have a basic sense for how much land there is in Manhattan. Maybe you do too?

Why not tap into this intuition, and see if we can use it to understand Greenland’s ice. If Manhattan doesn’t work for you, try to find a local geographical area that you’re familiar with instead.

Wikipedia tells me that the land area of Manhattan is about 59 square kilometers (km²), or 59 million square meters (m²). Here’s what I want to know:

If we stacked all the ice that Greenland lost in 2019 over Manhattan, how high would it reach?

If I had to guess, I’d say the answer might be on the order of 100 meters (roughly 30 stories high). Maybe you have your own guess for what you think the answer should be? It’s helpful to explicitly articulate these guesses, even if it’s just based on a vague feeling, because it gives you a sense for whether the actual answer is surprising.

Here’s a map of Lower Manhattan.

And here’s what my guess of a 30 story (100 m) tall ice sheet looks like.

When zoomed out, my guess looks like this.

OK, now let’s crunch the numbers.

If we divide a volume by an area, we get a height (m³/m² = m). So dividing 580 billion cubic meters by 59 million square meters, I get an answer of 10 thousand meters, i.e. 10 kilometers (a little over 6 miles).

(Another mini-tip: if two numbers are close, you can treat them as equal for the purpose of approximation. The difference between 58 and 59 isn’t relevant when we’re after a ballpark answer. There’s a lovely Hindi phrase for this — unees-bees ka farak — which literally means ‘(ignoring) the difference between 19 and 20’, and is used to convey an approximate result. Every number in this post is unees-bees ka farak.)

If all the ice that Greenland lost in 2019 were stacked over Manhattan, it would reach a height of 10 km (~6 miles, or 3000 stories). Here’s what this would look like.

This is taller than Mt. Everest, which stands under 9 km tall. Personally I find this astonishing — it’s two orders of magnitude larger than my guess.

Strategy 3: Divide by Another Big Number

This is my favorite strategy for dealing with big numbers. In fact, we already used this strategy above when dividing the volume of Greenland’s lost ice (a big number) by the land area of Manhattan (another ‘big’ number).

The reason we ended up with such a massive height is that Greenland lost a lot of ice, and the area of Manhattan is not very large. If instead we divided by the area of California, we’d end up with a height of 1.5 meters (or 5 feet). Greenland lost enough ice in 2019 to cover California to a height of 5 feet.

What are some other big numbers we could divide by?

How about the number of people on Earth? If we divided the ice Greenland lost in 2019 between the 7.8 billion people on the planet, each person would end up with 580 billion / 7.8 billion ~ 74 cubic meters ~ 2,600 cubic feet.

Hmm, that’s still a pretty large number, so let’s divide it again, this time by the number of days in a year. That gives 2,600 / 365 ~ 7 cubic feet, which happens to be the volume of this freezer. (Mini-tip: sometimes you get lucky just by Googling for an awkward number, as long as you provide units.)

Arctic King 7 cu ft Chest Freezer, Black - Walmart.com ...

So Greenland’s 2019 ice loss, when divided among everyone on Earth, comes out to a freezer’s worth of ice per person per day. By dividing a large number by another large number, we can bring it down to a human-sized number.

Alternatively, another large number you could divide by is the number of minutes in a year. 1 year = 365 * 24 * 60 minutes = 525,600 minutes. (Or just remember the song from Rent.)

525600 Minutes GIF - SeasonsOfLove Play 525600Minutes GIFs

So the rate at which Greenland lost ice in 2019 is 580 billion cubic meters / 525,600 minutes, which is a bit over a million cubic meters per minute.

As it turns out, a million cubic meters happens to be about the volume of the Empire State Building. So in 2019, Greenland lost around 1 Empire State Building worth of ice every minute.

That’s a lot of ice.

Empire State Building 3D Model by Thomas De Rivaz

To recap: when faced with a big unfamiliar number, first express it in familiar units, and then find ways to divide it down to size. Keep going, until you get to something that’s small enough that you have a relatable comparison for it. You’ll sometimes see this strategy used in news coverage. For example, this story divides Greenland’s ice melt by the area of the UK. And this one divides it by the seconds in a year (and yes, even expresses the result in that classic science-writing cliche: Olympic-sized swimming pools. If you’re curious, the answer comes out to 7 swimming pools per second).


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This Week In Climate News

Heat waves, wildfires, heat records, melting ice sheets, and more.

How Decades of Racist Housing Policy Left Neighborhoods Sweltering

In the previous newsletter, we talked about the idea of shade inequality, where low-income communities have more paved areas and fewer green spaces, while high-income communities have the opposite. The consequence is a significant difference in temperature, resulting in the creation of urban heat islands.

This week in NYT, Brad Plumer and Nadja Popovich have a scrolling graphic article on how neighborhoods in Richmond, Virginia that were redlined in the 1930s because the majority of residents were Black are now “some of the hottest parts of town in the summer, with few trees and an abundance of heat-trapping pavement.” Meanwhile, “White neighborhoods that weren’t redlined tend to be much cooler today — a pattern that repeats nationwide.” This is an example of how decades of systemic racism is causing the climate crisis to disproportionately impact Black Americans.

Plumer and Popovich’s work is consistently excellent, so I highly recommend checking it out. Some highlights:

Across more than 100 cities, a recent study found, formerly redlined neighborhoods are today 5 degrees [F] hotter in summer, on average, than areas once favored for housing loans, with some cities seeing differences as large as 12 degrees [F]. Redlined neighborhoods, which remain lower-income and more likely to have Black or Hispanic residents, consistently have far fewer trees and parks that help cool the air. They also have more paved surfaces, such as asphalt lots or nearby highways, that absorb and radiate heat.

Even small differences in heat can be dangerous, scientists have found. During a heat wave, every one degree [F] increase in temperature can increase the risk of dying by 2.5 percent. Higher temperatures can strain the heart and make breathing more difficult, increasing hospitalization rates for cardiac arrest and respiratory diseases like asthma. Richmond’s four hottest ZIP codes all have the city’s highest rates of heat-related emergency-room visits.

The Impact of Heatwaves on LA’s Homeless Community

By Alexandria Herr in Grist:

Heat waves are the deadliest weather-related event to hit cities every year, killing on average 702 people annually nationwide, and their impact will only worsen with climate change. For the nation’s 568,000 homeless people, 66,000 of whom live in Los Angeles County, the heatwave is adding to the challenges of a population already vulnerable to the crises of COVID-19, climate change, and police brutality.

Heat, Smoke and COVID are Battering Farm Workers

By Somini Sengupta in NYT:

Most [agricultural workers in California] are immigrants from Mexico. Mostly, they earn minimum wage ($13 an hour in California). Mostly, they lack health insurance and they live amid chronic pollution, making them susceptible to a host of respiratory ailments.

Climate change exacerbates these horrors.

By noon one day last week, temperatures had soared to 100 degrees Fahrenheit in Lodi, in the valley’s northern stretch. Still, Leonor Hernández, 38, mother of three, was at work. [..]

As the week progressed and more acres burned, the air grew increasingly toxic. Her head and chest hurt. She was coughing. The San Joaquin Valley Air Pollution Control District urged residents to stay indoors.

Good advice, in theory, Ms. Hernández said. “But we need to work, and if we stay indoors we don’t get paid,” she said. “We have bills for food and rent to pay.”

via Brooke Jarvis

How US Corporate Interests are Short Circuiting Climate Action

This was a brilliant, illuminating interview with climate policy expert Leah Stokes in the Columbia Energy Exchange podcast. Stokes is an excellent public speaker, and she clearly breaks down how corporate interests in the US spend vast amounts of money to stall climate progress. While I was aware of this in theory, the specifics are eye-opening. I’ll be listening to this a few times to absorb all this information, and I highly recommend that you check it out. Stokes has a new book on this topic, called Short Circuiting Policy.

The Climate Is Becoming an Increasingly Important Issue for Voters

According to a new survey of a thousand US Americans, roughly 80% accept that Earth’s temperature has been increasing over the past 100 years, that it will increase over the next 100 years, and that humans are at least partly reponsible. The data shows that these views have been remarkably consistent over the past two decades, although people’s confidence in their views has been on the rise in recent years.

John Schwartz at NYT reports on this study. Jon Krosnick, a leader of the study, told NYT that the percentage of people who feel climate change is an extremely important issue to them personally is now 25%, up from 13% in 2015, “trailing only the group focused on abortion, at 31 percent.”

In Other Climate News

👉🏽 According to two new studies, the Greenland ice sheet may be approaching a tipping point of uncontrollable melting. The melt from Greenland alone is the largest single contributor to rising sea levels.

BBC News reports:

"The result for 2019 confirms that the ice sheet has returned to a state of high loss, in line with the IPCCs worst-case climate warming scenario," said Prof Andy Shepherd from Leeds University, who is the co-lead investigator for Imbie [Ice Sheet Mass Balance Inter-comparison Exercise].

'This means we need to prepare for an extra 10cm or so of global sea level rise by 2100 from Greenland alone."

[..]

"If Greenland's ice losses continue on their current trajectory, an extra 25 million people could be flooded each year by the end of this century."

👉🏽 Want to reduce the carbon footprint of your food? Focus on what you eat, not whether your food is local.

I was surprised to learn that transport makes up a surprisingly small fraction of the carbon footprint of what we eat, and found this chart immensely helpful.

👉🏽 How China’s Expanding Fishing Fleet Is Depleting the World’s Oceans

👉🏽 Policy expert Bina Venkataraman interviews climate scientist Ayana Elizabeth Johnson in The Boston Globe:

I also just don’t see how we win at addressing the climate crisis unless we involve people of color. It is not a merely technical challenge that we’re facing. It’s not like we can get a bunch of engineers in a room and then climate change will be solved. It is about how we implement solutions. It is about how we replicate and scale them. It is about how communities change the way that they do things. It is about agriculture and buildings and transportation and electricity. Solving the climate crisis is about everything. And so we need to find ways that everyone can be a part of this transformation that we need and be a part of the plentiful solutions that we already have available.

Research done at Yale and George Mason Universities shows people of color are more concerned already about the climate crisis. Wouldn’t it make sense to prioritize the people who are already on board who already care? The climate crisis is so big that we need to build the biggest possible team.

👉🏽 California wildfires have charred 1.2 million acres, with more than 100,000 evacuees

👉🏽 Meanwhile, Death Valley may have recorded the hottest ever temperature on Earth. NYT and Washington Post report.

👉🏽 This was a fascinating chemistry-packed video by Alex Dainis on the science of the ozone hole and CFCs. She describes a chain reaction through which a single Chlorine atom can destroy up to 100 thousand Ozone molecules! And while the ozone hole has been shrinking, recent ozone emissions from China have been undoing some of this progress. If you’re interested in digging into the data, the NASA Ozone Watch page is packed with graphs and visualizations.

👉🏽 Extreme Arctic fires are become the new normal

McCarty has searched through the scientific literature from Arctic nations as part of a report she is co-authoring for the Arctic Council. “This is the type of fire event that would be described by these worst-case modeling scenarios that were supposed to occur mid-century,” she said, adding that we may be 30 years early in seeing such fire impacts, which would require a reevaluation of how the Arctic is responding to global warming.

Via Brooke Jarvis

👉🏽 Last decade was Earth's hottest on record.

👉🏽 Washington Post has an excellent series on the places in the US already experiencing more than 2 degrees C of warming. Juliet Eilperin, Carolyn Van Houten and John Muyskens report on a 20 year drought in Western Colorado.

👋🏽 That’s all for this week. Thanks for reading! You can follow me on Twitter and support my work on Patreon.

Air Inequality, Heat Waves & Siberian Fires

"The first place to start is race and racism."

Air Inequality

Air Pollution Is Much Worse Than You Might Think

👉🏽 At Vox, David Roberts reports on new research on the dramatic effect that US action on climate change would have on the health of US Americans:

The numbers are eye-popping. [Duke University climate scientist & IPCC report lead author Drew Shindell] testified: “Over the next 50 years, keeping to the 2°C pathway would prevent roughly 4.5 million premature deaths, about 3.5 million hospitalizations and emergency room visits, and approximately 300 million lost workdays in the US.

He quotes from Shindell’s testimony to the House Committee on Oversight and Reform:

On average, this amounts to over $700 billion per year in benefits to the US from improved health and labor alone, far more than the cost of the energy transition.

In other words, dropping fossil fuels would pay for itself from an air quality perspective alone. Roberts makes the important point that although curtailing the warming effects of climate change requires globally coordinated action, the air quality benefits are local, making the rewards more directly tangible. He quotes Rebecca Saari, an air quality expert at the University of Waterloo, who says, “The air quality ‘co-benefits’ are generally so valuable that they exceed the cost of climate action, often many times over.

So national (& even more local) level climate action will lead to outsized health and economic benefits from air quality improvements. And global air pollution hotspots like China and India stand to gain immeasurably from improving air quality.

And if this is true in the US — which, after all, has comparatively clean air — it is true tenfold for countries like China and India, where air quality remains abysmal. A Lancet Commission study in 2017 found that in 2015, air pollution killed 1.81 million people in India and 1.58 million in China.

Shindell’s research reveals that those estimates may be woefully low. [..] The true toll may be almost double that

👉🏽 If you’d like to follow updates on the air inequality crisis (with an emphasis on South Asia), here are some great Twitter accounts to follow: State of Global Air, Air Quality in India, Care for Air, Clean Air Fund, Center for Research on Energy and Clean Air, Air South Asia, Open Air Quality, Christa Hasenkopf, and Pallavi Pant.

The Deadly Mix of COVID-19, Air Pollution, and Inequality

👉🏽 Also at Vox, Lois Parshley has an excellent, sobering piece:

On April 5, a pre-print study released by the Harvard T.H. Chan School of Public Health directly linked air pollution to the probability of more severe Covid-19 cases. That joins decades of scientific literature that suggest race and income impact how much chronic air pollution you are exposed to. And it could be a major factor in the disproportionate Covid-19 mortality rates we’re now seeing in non-white populations.

In Louisiana, for example, black people represent 32 percent of the population and 70 percent of the Covid-19 deaths. In Wisconsin — in what its Gov. Tony Evers has called “a crisis within a crisis” — black people account for six percent of the population, and half of the Covid-19 deaths. In Michigan, 12 percent of residents are black, but account for 32 percent of deaths. Latinx populations show similarly disproportionate rates: in New York City, Hispanic people represent 29 percent of the population, and 34 percent of the city’s deaths — the largest percentage by race.

[..]

Mychal Johnson, a Bronx resident and co-founding member of the advocacy group South Bronx Unite, says that in the Bronx, “We already had higher rates of children missing school because they had to go to the hospital for respiratory problems.” Every year, the Bronx has 21 times more asthma hospitalizations than other New York boroughs, and over five times the national average.

The neighborhood, Johnson says, is known as “asthma alley,” and he and his family breathe the emissions of the hundreds of diesel trucks that stream from the neighborhood’s warehouses and along local highways. It is not unrelated that 44 percent of the Bronx is black. Nationwide, black children are 500 percent more likely to die from asthma than white children, and have a 250 percent higher hospitalization rate for the condition.

The article links to a pre-print study that finds that an increase of 1 μg/m3 in PM 2.5 (a relatively small increase in the most harmful category of air pollution, consisting of tiny particles with sizes under 2.5 microns) is associated with an 8% increase in the COVID-19 death rate.

Connecting the Dots Between Environmental Injustice and COVID-19

👉🏽 An excellent interview with Sacoby Wilson, a University of Maryland professor and scientist focusing on health issues related to environmental injustice, by Katherine Bagley in Yale e360.

Covid-19 has shown that we have a lot of Haves in this country, but we have a lot more Have-Nots. Our policies have disproportionally benefited the Haves while disproportionately impacting the Have-Nots. To address the disparities in Covid-19, we have to address our structural inequalities in this country. The first place to start is race and racism.

Wilson makes the point that scientific research is underserving the most vulnerable communities by failing to adequately assess the risk from more pollutants.

But what’s more egregious is we’re not really using advanced science to understand the true exposure profiles of those local populations. [..] So, PM2.5 is a pollutant that, it was shown in the Harvard study, could increase mortality rates with Covid-19. Now PM2.5 itself causes asthma, heart disease, stroke. It elevates blood pressure. It increases infant mortality rates. It can cause birth defects. It can cause low-birth-weight births. It also can cause diabetes, cancer, premature mortality. That’s PM2.5 by itself. What if you add ultra-fine particles? What if you add black carbon, which is a byproduct of diesel exhaust?

Does air pollution increase the risk of dying from COVID-19? (Yes.)

👉🏽 Damian Carrington at The Guardian reports on a new study by the UK Office for National Statistics of over 46,000 COVID deaths in England, showing that “a small, single-unit increase in people’s exposure to small-particle pollution over the previous decade may increase the death rate by up to 6%. A single-unit increase in nitrogen dioxide, which is at illegal levels in most urban areas, was linked to a 2% increase in death rates.

So there’s a growing body of evidence that air pollution is linked to an increase in the COVID-19 mortality rate. When you couple this with the fact that non-white communities are more likely to live in areas with higher air pollution, this lays bare one more way in which the affects of fossil fuel consumption and COVID-19 are disproportionately borne by black and brown communities.


Heat Waves

👉 In NYT, Somini Sengupta has an unmissable piece on how heatwaves disproportionately impact poorer and more vulnerable populations, profiling refugees, laborers, farmers, immigrants, and elderly people across multiple continents.

In the United States, heat kills older people more than any other extreme weather event, including hurricanes, and the problem is part of an ignominious national pattern: Black people and Latinos like Mr. Velasquez are far more likely to live in the hottest parts of American cities.

His neighborhood is exceptionally vulnerable to heat extremes. According to the most recent available data, from 2018, Brownsville was among New York City’s hottest, with average daytime highs around two degrees Fahrenheit higher than the city as a whole.

Those neighborhoods are often the same areas that have faced some of the highest rates of coronavirus deaths. This spring, around 10 residents of Mr. Velasquez’s senior housing complex died from the virus.

Inequality exacerbates climate and environmental risks,” said Kizzy Charles-Guzman, a deputy director for resilience efforts in the New York City Mayor’s office.

👉🏽 Lisa Collins at NYT reports on how a warming climate is changing the ecosystem of New York, causing difficulties for native plants, while subtropical plants are thriving, and invasive pests and weeds are growing out of control. This sentence blew my mind:

New York City, after years of being considered a humid continental climate, now sits within the humid subtropical climate zone. The classification requires that summers average above 72 degrees Fahrenheit — which New York’s have had since 1927 — and for winter months to stay above 27 degrees Fahrenheit, on average. The city has met that requirement for the last five years, despite the occasional cold snap. And the winters are only getting warmer.

👉🏽 At Yale E360, Jim Robbins looks at how a warming climate will impact agriculture and how researchers are trying to breed more resilient crops and livestock.

👉🏽 Baghdad’s record heat offers glimpse of world’s climate change future. By Louisa Loveluck and Chris Mooney in the Washington Post.

Warming in [Iraq] is far above average. Data from Berkeley Earth show that, compared with the country’s temperature at the close of the 19th century (1880-1899), the last five years were 2.3 degrees Celsius, or 4.1 degrees Fahrenheit, hotter. The Earth as a whole has only warmed by about half that amount over the same time period. [..]

A desert country like Iraq is warming more rapidly, explained MIT climate expert Elfatih Eltahir, because it is so dry. While additional heat in many places would partially go toward evaporating moisture in the soil, there just isn’t much such moisture in Iraq.

👉🏽 I also recommend checking out this 99% Invisible episode from January on Shade Inequality in Los Angeles.

Today, in Los Angeles, shade is distributed to people who can afford it. If you go into neighborhoods that were designed to be wealthy residential enclaves, the sidewalks are wider and include strips of grass four to ten feet wide, for the easy planting of thick, leafy trees.

Hancock Park, for example, is a flat neighborhood, landlocked in the center of the city. There is nothing about it that naturally lends itself over to being a lush, verdant tree canopy. But the neighborhood was developed as an exclusive, wealthy residential enclave. And when that happened, the power lines were moved underground and the layout was designed specifically to allow for tree growth. This is not the case for other large residential areas across Los Angeles. 


Siberian Fires

👉🏽 On June 20, the town of Verkhoyansk in Siberia experienced a record-breaking high temperature of 38°C (100°F), the highest temperature recorded north of the Arctic Circle. A study published by the UK Met Office concluded that this would be extremely unlikely without human-caused climate change.

The results showed with high confidence that the January to June 2020 prolonged heat was made at least 600 times more likely as a result of human-induced climate change.

The study goes on to point out that

About 7,900 square miles of Siberian territory had burned so far this year as of June 25, compared to a total of 6,800 square miles as of the same date a year ago, according to official data, these fires led to a release of 56 Megatons of CO2 in June 2020, more than the yearly CO2 emissions of some countries (e.g., Switzerland).

👉🏽 Meanwhile, Andrew Kramer reported in the New York Times on one of the many environmental consequences of the warming Siberian permafrost.

Diesel fuel spilled from a tank that burst last week after settling into permafrost that had stood firm for years but gave way during a warm spring, Russian officials said. [..]

The spill released about 150,000 barrels of diesel into a river, compared with about 260,000 barrels of crude oil released into Prince William Sound during the Exxon tanker accident, a touchstone for environmental damage from petroleum spills.

👉🏽 Madeleine Stone reports in National Geoographic:

If fire becomes a regular occurrence on Siberia’s thawing tundra, it could dramatically reshape entire ecosystems, causing new species to take over and, perhaps, priming the land for more fires. The blazes themselves could also exacerbate global warming by burning deep into the soil and releasing carbon that has accumulated as frozen organic matter over hundreds of years.

“This is not yet a massive contribution to climate change,” says Thomas Smith, an environmental geographer at the London School of Economics who has been tracking the Siberian fires closely. “But it’s certainly a sign that something different is happening.”

👉🏽 A NOAA NASA Satellite observed smoke from the Siberian fires extending all the way across the Bering Sea, and reaching Alaska.

Smoke and particulates from wildfires in Siberia extending all the way to Alaska. Image: NOAA/NASA

In Other Climate News

👉🏽 Leah Stokes is always great on summarizing climate policy:

👉🏽 Here’s a fascinating read by Cheryl Katz in Yale e360 digging in to the chemistry of Why Rising Acidification Poses a Special Peril for Warming Arctic Waters.

“The polar regions are especially vulnerable because of a systemic vulnerability that is linked to their chemical states today, which makes them very, very close to tipping over the edge into extremes of acidification,” says [climate scientist and IPCC report lead author Alessandro Tagliabue].

[..] As the carbonate levels in seawater decrease, mollusks and other shell-building creatures find it increasingly difficult to get enough ions to build and maintain their shells. And at a sufficiently low carbonate concentration — called undersaturation — the shells begin to corrode.

Models predict that large parts of the Arctic will cross this threshold as early as 2030, and researchers forecast that most Arctic waters will lack adequate aragonite for shell-building organisms by the 2080s.

👉🏽 On NPR’s On The Media, Vox writer David Roberts discusses how "shifting baselines syndrome" clouds our perspective on climate change.


👉🏽 Help Support My Writing 👈🏽

That’s all for this week! Apologies for the inadvertent 10-month-long hiatus in this newsletter (yikes!) I’ve been focusing my energy in 2020 on science writing work that helps me make rent (and also on trying to get by in this pandemic, just like everyone else).

On that note, I recently created a Patreon page. If you’d like to support my writing and be the first to know about all of my science communication projects, please consider becoming a patron. I simply can’t do the work I do without your support.

As a heads up, I’m also planning to add paid subscriptions to this newsletter to help support my climate writing — more on that soon. So if you’re primarily interested in supporting my climate work, that might be a better option for you.

And if you’re not in a position to contribute, that’s totally fine as well! Thank you so much for reading, and for showing up. ✌🏽💜

The Problem with '12 Years'

It's like the more carbon we come across, the more problems we see.

It’s been a long year.

It’s almost exactly a year since the Intergovernmental Panel on Climate Change came out with a major report describing what 1.5°C of warming will look like (I know, it feels like an eternity ago). Today we’re at about 1 degree of warming compared to pre-industrial times, so we’re already two-thirds of the way to this threshold.

This report catapulted the idea of carbon budgets into the zeitgeist. A carbon budget tells us how much carbon dioxide we can continue to emit and still have a reasonable chance of remaining below some particular threshold of warming.

Think of a carbon budget as the amount of money that remains in our carbon bank account, and our annual carbon emissions as our annual spending. As the IPCC famously warned us a year ago, at our current rate of emissions, we’ll burn through our budget for 1.5°C of warming in about 12 years.

Actually, the report didn’t say “12 years”. They leave it to you to do the math. The IPCC came up with carbon budgets for a reasonable shot at staying below 1.5°C of warming. If you divide these budgets by our annual emissions, you’ll find that at our current rate we’ll blow through them in a little over a decade. The report concludes that unless “global CO₂ emissions start to decline well before 2030”, we will surpass the 1.5°C threshold.

So that’s where ‘12 years’ comes from. Some people believe that this a simple and effective slogan that captures the urgency of our climate crisis, and has helped galvanize people into action. Others feel that it’s overly simplistic at best, and misleading at worst, because it singles out a specific number as an all-or-nothing target, whereas in reality the effects of climate change are a continuum. As climate scientist Kate Marvel put it, “Climate change isn’t a cliff we fall off, but a slope we slide down”.

But that’s not what I want to discuss here, there are already many good pieces on this debate. Instead, I want to know where carbon budgets come from in the first place. What’s the justification for these numbers, and how accurate are they?

So in this post, I’m going to take you through how you can look at the data for yourself and come up with a rough estimate of the carbon budget.

Let’s start with the basics

You’re probably very used to seeing graphs depicting global warming that look like this. (I just doodled this, so don’t take the exact shape too seriously. )

These kinds of graphs are great for showing us how much the Earth has warmed. (And as Ronnie Chieng hilariously pointed out, they even work upside down.)

ronnie-chieng-climate-change.jpg » LiveScience

Although these graphs teach us about the past, they aren’t so helpful when it comes to predicting the future. It’s hard to tell by looking at this graph which way we’re headed, because that depends on how much carbon dioxide humans will emit in the future.

Let’s go ahead and create this graph using public data. The Global Warming Index is a measure of how much of Earth’s temperature rise is attributable to humans (so it’s removing all of the natural fluctuations in temperature).

Here’s what this looks like, wen plotted versus time (interactive version here).

Notice how it shoots up around 1970? You can compare that to a historical graph of carbon dioxide emissions and work out why that happens.

The reason this graph isn’t so useful for predicting the future is that its slope (how steeply it rises) depends on how much carbon dioxide is in the air. A future in which we take major climate action will follow a very different trajectory compared to a future that’s business as usual.

It turns out that there’s another simple way to look at our historical climate trajectory, one that’s more helpful for predicting the future.

Another way to think about warming

Here’s how it works. Imagine that you change the x-axis of the graph so that instead of measuring the years go by as we did above, we instead measure how much carbon dioxide we’ve added to the air. In that case, the graph might end up looking like this.

Every year, we add some more CO₂ to the air, so we take a step further to the right. Consequently, the Earth warms up. For every step to the right, we also take a step up. So you’d expect our trajectory to move towards the top-right.

If we make this switch, here’s what this new graph looks like (interactive).

In the graph above, the horizontal axis represents the total amount of carbon dioxide that we’ve emitted, due to both fossil fuels and land use. I pulled these numbers from the Global Carbon Project. The vertical axis measures how much the world has warmed as a consequence. Let’s call this graph a climate carbon curve.

The animation shows us the history of human-caused global warming. Every dot represents a single year of human history. Each year we emit more CO₂, so we take a step to the right. And for every step to the right, we warm up, so we take a step up. Notice that as global annual emissions accelerate, the dots get further and further apart — we’re taking bigger steps along the climate carbon curve.

Do you notice anything interesting about this graph? Let’s draw a line connecting the first and last points on this graph.

When viewed in this way, the history of climate change is surprisingly simple to understand. Aside from a bump in the 1970s, the global historical climate trajectory from 1850 to 2017 essentially follows a straight line on the climate carbon curve.

That’s a simple message. In spite of all of the complexity in climate science, there’s a direct proportionality between how much total carbon dioxide we’ve pumped out, and how much the planet has warmed as a result. For every trillion tonnes of carbon dioxide that we emit, the graph teaches us that we raise Earth’s temperature by about 0.44 degrees Celsius. To paraphrase Notorious B.I.G., the more carbon we come across, the more problems we see.

Although the exact slope might differ, this straight-line relationship is born out both through historical observations as well as through every serious climate simulation. There are dozens of scientific papers demonstrating that this relationship holds.

A caveat: We’re talking about how much the temperature rises soon after we dump greenhouse gases into the air. Climate scientists call this the effective transient response of the climate to cumulative carbon emissions (quite the mouthful). Once this carbon is in the air, the temperature will gradually continue to rise further, over centuries. The long-term temperature rise is known as the equilibrium climate sensitivity, which is a fair bit higher than the transient climate response.

Why a straight line?

It’s somewhat puzzling that this graph is so simple. What causes this straight-line relationship? Why should every unit of carbon dioxide, whether emitted in the past or the future, have the same warming effect?

If you only consider carbon dioxide in the air, then every subsequent unit of carbon dioxide does indeed have slightly less of a warming ‘bite’. That’s because the atmosphere gets increasingly saturated with CO₂ over time. It’s a bit like how throwing mud into murky water has less of an effect than throwing it into clear water.

So by itself, every additional unit of carbon dioxide that we emit would have a slightly diminishing warming effect. However, as we emit more CO₂, the oceans also become more saturated with the gas. This means that they’ll have less room to absorb carbon dioxide in the future, so a larger fraction of our emissions will end up in the air.

So we’ve got two opposing effects. As the air gets saturated with carbon dioxide, every additional unit of the gas has slightly less of a warming effect. At the same time, as the oceans get saturated with carbon dioxide, more of the gas will end up in the air.

As it turns out, these two effects cancel each other out. The result is that every new unit of carbon dioxide has approximately the same warming effect as the previous one. This is why we end up with this straight-line relationship between CO₂ and warming. (You can read more about this here, or check out the papers linked above.)

What comes next?

The big question is, where are we going to end up in the future?

We can take a reasonable guess by extrapolating out trajectory forwards.

Every possible climate future, in one graph

The yellow line represents our current trajectory, extrapolated into the future. I’ve also added a ‘cone of uncertainty’ around it. That’s because, in reality, there are bounded gaps in our knowledge (i.e., uncertainties). This cone approximately represents the uncertainty in our prediction, which comes from the underlying uncertainty in the historical measurements and analyses.

This graph isn’t telling us about just one climate future. Instead, it places a bound on every possible climate future. Trace your finger upwards along the cone of uncertainty and you’re tracing out a possible future. A high carbon future is one where your finger moves further along the cone, a low carbon future is one where your finger doesn’t move as far.

Notice that even if we shrink our annual climate emissions down to a tiny fraction of its current value, this won’t completely halt global warming. We’ll still be inching up along the cone, just taking smaller steps. The only way to stop the warming is to stop taking any steps at all. To stabilize Earth’s temperature, we need to get to zero emissions.

D.I.Y. Carbon Budgets

As promised, let’s use this graph to work out a carbon budget. By the end of 2017, we were at ~1° of warming, having emitted ~2300 billion tons of CO₂.

Trace your finger along the thin grey 1.5° line on the graph until it intersects the cone (for greater accuracy, you can zoom in with your cursor in this interactive graph).

You’ll see that it crosses the red shaded region and yellow line at about 3000, 3500, and 4200 billion tons. (These numbers are all rounded to the closest 100 billion tons.) To calculate our remaining carbon budget, subtract 2300 (where we are today) from these numbers.

So this graph tells us that as of 2018, our 1.5°C carbon budget ranged from 700 to 1900 billion tons of CO₂, with a best guess of 1200 billion tons.

Going through the same exercise for the 2°C budget, we come up with a carbon budget ranging from 1600 to 3200 billion tons, with a best guess of 2300 billion tons.

Compared to the IPCC predictions, these numbers are all on the high side. However, they’re in the ballpark of existing estimates of the carbon budget made from historical observations.

The IPCC predictions are created using climate models combined with observations. In general, this approach predicts a steeper slope for the climate carbon curve than purely historical observations do. The steeper the slope, the faster we’ll warm up. This is why the IPCC arrives at a smaller carbon budget than our simple method.

The Takeaway

We’ve seen how extending our historical trajectory forwards gives us a simple way to predict our climate future, and estimate carbon budgets. However, it’s important to keep in mind that all such estimates tend to have very large uncertainties.

We can confidently say that as we continue emitting carbon dioxide, we’re going to move further up the cone of uncertainty and warm up. We can use this idea to estimate when we’ll cross any particular threshold. But that’s all that these numbers are — approximate, ballpark estimates.

When people say that we have 12 years to use up our carbon budget, we should read that as ‘12 years give or take 10 or 15 years’. 12 years is not a sharp dividing line, it’s just a rough indicator of a wide range of uncertainty. What’s more, small changes in our underlying measurements and assumptions significantly shift these predictions (as the IPCC did last year). So to take this number as literal and unambiguous truth is to deeply misunderstand what it means.

That’s why some critics argue that rather than focus on impossibly precise carbon budgets, we should instead talk about when we’ll reach zero emissions. Because one thing that we can say with certainty is that so long as we’re still emitting carbon dioxide, we’re going to keep warming up.

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