Can We Fix The Air?

12 January, 2020

A slightly different version of this article I wrote first appeared in Nautilus on November 28, 2019.


Water rushes into Venice’s city council chamber just minutes after the local government rejects measures to combat climate change. Wildfires consume eastern Australia as fire danger soars past “severe” and “extreme” to “catastrophic” in parts of New South Wales. Ice levels in the Chukchi Sea, north of Alaska, hit record lows. England sees floods all across the country. And that’s just this week, as I write this.

Human-caused climate change, and the disasters it brings, are here. In fact, they’re just getting started. What will things be like in another decade, or century?

It depends on what we do. If our goal is to stop global warming, the best way is to cut carbon emissions now—to zero. The United Kingdom, Denmark, and Norway have passed laws requiring net zero emissions by 2050. Sweden is aiming at 2045. But the biggest emitters—China, the United States, and India—are dragging their heels. So to keep global warming below 2 degrees Celsius over pre-industrial levels by 2100, it’s becoming more and more likely that we’ll need negative carbon emissions:

That is, we’ll need to fix the air. We’ll need to suck more carbon dioxide out of the atmosphere than we put in.

This may seem like a laughably ambitious goal. Can we actually do it? Or is it just a fantasy? I want to give you a sense of what it would take. But first, here’s one reason this matters. Most people don’t realize that large negative carbon emissions are assumed in many of the more optimistic climate scenarios. Even some policymakers tasked with dealing with climate change don’t know this.

In 2016, climate scientists Kevin Anderson and Glen Peters published a paper on this topic, called “The trouble with negative emissions.” The title is a bit misleading, since they are not against negative emissions. They are against lulling ourselves into complacency by making plans that rely on negative emissions—because we don’t really know how to achieve them at the necessary scale. We could be caught in a serious bind, with the poorest among us taking the biggest hit.

So, how much negative carbon emissions do we need to stay below 2 degrees Celsius of warming, and how people are hoping to achieve them? Let’s dive in!

In 2018, humans put about 37 billion tonnes of carbon dioxide into the air. A “tonne” is a metric ton, a bit larger than a US ton. Since the oxygen is not the problem—carbon dioxide consisting of one atom of carbon and two of oxygen—it might make more sense to count tonnes of carbon. But it’s customary to keep track of carbon by its carbon dioxide equivalent, so I’ll do that here. The National Academy of Sciences says that to keep global warming below 2 degrees Celsius by the century’s end, we will probably need to be removing about 10 billion tonnes of carbon dioxide from the air each year by 2050, and double that by 2100. How could we do this?

Whenever I talk about this, I get suggestions. Many ignore the sheer scale of the problem. For example, a company called Climeworks is building machines that suck carbon dioxide out of the air using a chemical process. They’re hoping to use these gadgets to make carbonated water for soft drinks—or create greenhouses that have lots of carbon dioxide in the air, for tastier vegetables. This sounds very exciting…until you learn that currently their method of getting carbon dioxide costs about $500 per ton. It’s much cheaper to make the stuff in other ways; beverage-grade carbon dioxide costs about a fifth as much. But even if they bring down the price and become competitive in their chosen markets, greenhouses and carbonation use only 6 million tonnes of carbon dioxide annually. This is puny compared to the amount we need to remove.

Thus, the right way to think of Climeworks is as a tentative first step toward a technology that might someday be useful for fighting global warming—but only if it can be dramatically scaled up and made much cheaper. The idea of finding commercial uses for carbon dioxide as a stepping-stone, a way to start developing technologies and bringing prices down, is attractive. But it’s different from finding commercial uses that could make a serious dent in our carbon emissions problem.

Here’s another example: using carbon dioxide from the air to make plastics. There’s a company called RenewCO2 that wants to do this. But even ignoring the cost, it’s clear that such a scheme could remove 10 billion tonnes of carbon dioxide from the air each year only if we drastically ramped up our production of plastics. In 2018, we made about 360 million tonnes of plastic. So, we’d have to boost plastic production almost ten-fold. Furthermore, we’d have to make all this plastic without massively increasing our use of fossil fuels. And that’s a general issue with schemes to fix the air. If we could generate a huge abundance of power in a carbon-free way—say from nuclear, solar, or wind—we could use some of that power to remove carbon dioxide from the atmosphere. But for the short term, a better use of that power is to retire carbon-burning power plants. Thus, while we can dream about energy-intensive methods of fixing the air, they will only come into their own—if ever—later in the century.

If plastics aren’t big enough to eat up 10 billion tonnes of carbon dioxide per year, what comes closer? Agriculture. I’m having trouble finding the latest data, but in 2004 the world created roughly 5 billion tonnes of “crop residue”: stems, leaves, and such left over from growing food. If we could dispose of most of this residue in a way that would sequester the carbon, that would count as serious progress. Indeed, environmental engineer Stuart Strand and physicist Gregory Benford—also a noted science fiction writer—have teamed up to study what would happen if we dumped bales of crop residue on the ocean floor. Even though this stuff would rot, it seems that the gases produced will take hundreds of years to resurface. And there’s plenty of room on the ocean floor.

Short of a massive operation to sink crop residues to the bottom of the sea, there are still many other ways to improve agriculture so that the soil accumulates more carbon. For example, tilling the land less reduces the rate at which organic matter decays and carbon goes back into the air. You can actually fertilize the land with half-burnt plant material full of carbon, called “biochar.” Planting crops with bigger roots, or switching from annual crops to perennials, also helps. These are just a few of the good ideas people have had. While agriculture and soil science are complex, and you probably don’t want to get into the weeds on this, the National Academy of Sciences estimates that we could draw down 3 billion tonnes of carbon dioxide per year from improved agriculture. That’s huge.

Having mentioned agriculture, it’s time to talk about forests. Everyone loves trees. However, it’s worth noting that a mature forest doesn’t keep on pulling down carbon at a substantial rate forever. Yes, carbon from the air goes to form wood and organic material in the soil. But decaying wood and organic material releases carbon back into the air. A climax forest is close to a steady state: the rate at which it removes carbon from the air is roughly equal to the rate at which it releases this carbon. So, the time when a forest pulls down the most carbon is when it’s first growing.

In July 2019, a paper in Science argued that the Earth has room for almost 4 million square miles of new forests. The authors claimed that as these new trees grow, they could pull down about 730 billion tonnes of carbon dioxide.

At first this sounds great. But remember, we are putting out 37 billion tonnes a year. So, the claim is that if we plant new forests over an area somewhat larger than the US, they will absorb the equivalent of roughly 20 years of carbon emissions. In short, this heroic endeavor would buy us time, but it wouldn’t be a permanent solution. Worse, many other authors have argued that the Science paper was overly optimistic. One rebuttal points out that it mistakenly assumed treeless areas have no organic carbon in the soil already. It also counted on a large increase of forests in regions that are now grassland or savanna. With such corrections made, it’s possible that new forests could only pull down at most 150 billion tonnes of carbon dioxide.

That’s still a lot. But getting people to plant vast new forests will be hard. Working with more realistic assumptions, the National Academy of Sciences says that in the short term we could draw down 2.5 billion tonnes of carbon dioxide per year by planting new forests and better managing existing ones. In short: If we push really hard, better agriculture and forestry could pull 5.5 billion tonnes of carbon dioxide from the air each year. One great advantage of both these methods is that they harness the marvelous ability of plants to turn carbon dioxide into complex organic compounds in a solar-powered way—much better than any technology humans have devised so far. If we ever invent new technologies that do better, it’ll probably be because we’ve learned some tricks from our green friends.

And here’s another way plants can help: biofuels. If we burn fuels that come from plants, we’re taking carbon out of the atmosphere and putting it right back in: net zero carbon emissions, roughly speaking. That’s better than fossil fuels, where we dig carbon up from the ground and burn it. But it would be even better if we could burn plants as fuels but then capture the carbon dioxide, compress it, and pump it underground into depleted oil and gas fields, unmineable coal seams, and the like.

To do this, we probably shouldn’t cut down forests to clear space for crops that we burn. Turning corn into ethanol is also rather inefficient, though the corn lobby in the U.S. has persuaded the government to spend lots of money on this, and about 40 percent of all corn grown in the U.S. now gets used this way. Suppose we just took all available agricultural, forestry, and municipal waste, like lawn trimmings, food waste, and such, to facilities able to burn it and pump the carbon dioxide underground. All this stuff ultimately comes from plants sucking carbon from the air. So, how much carbon dioxide could we pull out of the atmosphere this way? The National Academy of Sciences says up to 5.2 billion tonnes per year.

Of course, we can’t do this and also sink all agricultural waste into the ocean—that’s just another way of dealing with the same stuff. Furthermore, this high-end figure would require immensely better organization than we’ve been able to achieve so far. And there are risks involved in pumping lots of carbon dioxide underground.

What other activities could draw down lots of carbon? It pays to look at the biggest human industries: biggest, that is, in terms of sheer mass being processed. For example, we make lots of cement. Global cement production in 2017 was about 4.5 billion tons, with China making more than the rest of the world combined, and a large uncertainty in how much they made. As far as I know, only digging up and burning carbon is bigger: for example, 7.7 billion tons of coal is being mined per year.

Right now cement is part of the problem: To make the most commonly used kind we heat limestone until it releases carbon dioxide and becomes “quicklime.” Only about 7 percent of the total carbon we emit worldwide comes from this process—but that still counts for more than the entire aviation industry. Some scientists have invented cement that absorbs carbon dioxide as it dries. It has not yet caught on commercially, but the pressure on the industry is increasing. If we could somehow replace cement with a substance made mostly of carbon pulled from the atmosphere, and do it in an economically viable way, that would be huge. But this takes us into the realm of technologies that haven’t been invented yet.

New technologies may in fact hold the key to the problem. In the second half of the century we should be doing things that we can’t even dream of yet. In the next century, even more so. But it takes time to perfect and scale up new technologies. So it makes sense to barrel ahead with what we can do now, then shift gears as other methods become practical. Merely waiting and hoping is not wise.

Totaling up some of the options I’ve listed, we could draw down 1 billion tonnes of carbon dioxide by planting trees, 1.5 billion by better forest management, 3 billion by better agricultural practices, and up to 5.2 billion by biofuels with carbon capture. This adds up to over 10 billion tonnes per year. It’s not nearly enough to cancel the 37 billion tonnes we’re dumping into the air each year now. But combined with strenuous efforts to cut emissions, we might squeak by, and keep global warming below 2 degrees Celsius.

Even if we try, we are far from guaranteed to succeed—Anderson and Peters are right to warn about this. But will we even try? This is more a matter of politics and economics than of science and technology. The engineer Saul Griffith said that dealing with global warming is not like the Manhattan Project—it’s like the whole of World War II but with everyone on the same side. He was half right: We are not all on the same side. Not yet, anyway. Getting leaders who are inspired by these huge challenges, rather than burying their heads in the sand, would be a big step in the right direction.


How to Solve Climate Change

28 December, 2019

Happy New Year!

This podcast of an interview with Saul Griffith is a great way to start your year:

• Ezra Klein, How to solve climate change and make life more awesome.

Skip straight down to the bottom and listen to the interview! Or right click on the link below and

download the .mp3.

I usually prefer reading stuff, but this is only available in audio form—and it’s worth it.

One important thing he says:

We have not had anyone stand up and espouse a vision of the future that could sound like success.

I think it’s time to start doing that. I think I’m finally figuring out how. But this interview with Saul Griffith does it already!




Climate Technology Primer (Part 2)

13 October, 2019

Here’s the second of a series of blog articles:

• Adam Marblestone, Climate technology primer (2/3): CO2 removal.

The first covered the basics of climate science as related to global warming. This one moves on to consider technologies for removing carbon dioxide from the air.

I hope you keep the following warning in mind as you read on:

I’m focused here on trying to understand the narrowly technical aspects, not on the political aspects, despite those being crucial. This is meant to be a review of the technical literature, not a political statement. I worried that writing a blog purely on the topic of technological intervention in the climate, without attempting or claiming to do justice to the social issues raised, would implicitly suggest that I advocate a narrowly technocratic or unilateral approach, which is not my intention. By focusing on technology, I don’t mean to detract from the importance of the social and policy aspects.

The technological issues are worth studying on their own, since they constrain what’s possible. For example: to draw down as much CO2 as human civilization is emitting now, with trees their peak growth phase and their carbon stored permanently, could be done by covering the whole USA with such trees.


Climate Technology Primer (Part 1)

5 October, 2019

Here’s the first of a series of blog articles on how technology can help address climate change:

• Adam Marblestone, Climate technology primer (1/3): basics.

Adam Marblestone is a research scientist at Google DeepMind studying connections between neuroscience and artificial intelligence. Previously, he was Chief Strategy Officer of the brain-computer interface company Kernel, and a research scientist in Ed Boyden’s Synthetic Neurobiology Group at MIT working to develop new technologies for brain circuit mapping. He also helped to start companies like BioBright, and advised foundations such as the Open Philanthropy Project.

Now, like many of us, he’s thinking about climate change, and what to do about it. He writes:

In this first of three posts, I attempt an outsider’s summary of the basic physics/chemistry/biology of the climate system, focused on back of the envelope calculations where possible. At the end, I comment a bit about technological approaches for emissions reductions. Future posts will include a review of the science behind negative emissions technologies, as well as the science (with plenty of caveats, don’t worry) behind more controversial potential solar radiation management approaches. This first post should be very basic for anyone “in the know” about energy, but I wanted to cover the basics before jumping into carbon sequestration technologies.

Check it out! I like the focus on “back of the envelope” calculations because they serve as useful sanity checks for more complicated models… and also provide a useful vaccination against the common denialist argument “all the predictions rely on complicated computer models that could be completely wrong, so why should I believe them?” It’s a sad fact that one of the things we need to do is make sure most technically literate people have a basic understanding of climate science, to help provide ‘herd immunity’ to everyone else.

The ultimate goal here, though, is to think about “what can technology do about climate change?”


Divesting

18 September, 2019

Christian Williams

John always tells me to write short, sweet, and clear. Knowing that his advice is supreme on these matters, I’ll try to write mini-posts in between the bigger ones. But… not this time – the topic is too good.

(Dispossess of property/authority. Say it, sound smart.)

…..

Work smarter, not (just) harder.

Today I got an email from Bill McKibben, founder of 350.org. (350 parts per million, the concentration of CO2 considered a “safe upper limit” for Earth, by NASA scientists James Hansen. We’re soaring past 415ppm.) In preparation for the global climate strike, Bill wants to share an important idea: divesting from fossil fuels may be our greatest lever.

Money is the Oxygen on which the Fire of Global Warming Burns

I’ll pluck paragraphs to quote, but please read the whole article; this is an extremely important and practical idea for addressing the crisis. And it’s well written… the first sentence sounds fairly Baezian.

I’m skilled at eluding the fetal crouch of despair—because I’ve been working on climate change for thirty years, I’ve learned to parcel out my angst, to keep my distress under control. But, in the past few months, I’ve more often found myself awake at night with true fear-for-your-kids anguish. This spring, we set another high mark for carbon dioxide in the atmosphere: four hundred and fifteen parts per million, higher than it has been in many millions of years. The summer began with the hottest June ever recorded, and then July became the hottest month ever recorded. The United Kingdom, France, and Germany, which have some of the world’s oldest weather records, all hit new high temperatures, and then the heat moved north, until most of Greenland was melting and immense Siberian wildfires were sending great clouds of carbon skyward. At the beginning of September, Hurricane Dorian stalled above the Bahamas, where it unleashed what one meteorologist called “the longest siege of violent, destructive weather ever observed” on our planet.

Bill emphasizes that change has moved far too slowly, of course. But he’s spent the past week with Greta Thunberg and many other activists, and one can tell that he really is heartened.

It seems that there are finally enough people to make an impact… what if there were an additional lever to pull, one that could work both quickly and globally?

The answer: money.

Today it is large corporations which have the greatest power over daily life, and they are far more susceptible to pressure and change then the insulated bureaucracies of governments.

Thankfully Bill and many others knew this years ago, and started a divestment campaign of breathtaking magnitude:

Seven years ago, 350.org helped launch a global movement to persuade the managers of college endowments, pension funds, and other large pots of money to sell their stock in fossil-fuel companies. It has become the largest such campaign in history: funds worth more than eleven trillion dollars have divested some or all of their fossil-fuel holdings.

$11,000,000,000,000.

And it has been effective: when Peabody Energy, the largest American coal company, filed for bankruptcy, in 2016, it cited divestment as one of the pressures weighing on its business, and, this year, Shell called divestment a “material adverse effect” on its performance.

The movement is only growing, accelerating, and setting its sights on the big gorillas. The main sectors: banking, asset management, and insurance.

Consider a bank like, say, JPMorgan Chase, which is America’s largest bank and the world’s most valuable by market capitalization. In the three years since the end of the Paris climate talks, Chase has reportedly committed 196 billion dollars in financing for the fossil-fuel industry, much of it to fund extreme new ventures: ultra-deep-sea drilling, Arctic oil extraction, and so on. In each of those years, ExxonMobil, by contrast, spent less than 3 billion dollars on exploration, research, and development. $196B is larger than the market value of BP; it dwarfs that of the coal companies or the frackers. By this measure, Jamie Dimon, the C.E.O. of JPMorgan Chase, is an oil, coal, and gas baron almost without peer.


But here’s the thing: fossil-fuel financing accounts for only about 7% of Chase’s lending and underwriting. The bank lends to everyone else, too—to people who build bowling alleys and beach houses and breweries. And, if the world were to switch decisively to solar and wind power, Chase would lend to renewable-energy companies, too. Indeed, it already does, though on a much smaller scale… It’s possible to imagine these industries, given that the world is now in existential danger, quickly jettisoning their fossil-fuel business. It’s not easy to imagine—capitalism is not noted for surrendering sources of revenue. But, then, the Arctic ice sheet is not noted for melting.

Bill elucidates the fact that it is critical to effect the divestment of giants like Chase, Blackrock, and Chubb. Even if these targets are quite hard, this method of action applies to every aspect of the economy, and empowers every single individual (more below). If the total divestment is spread over a decade, it can be done without serious economic instability. And if done well, it will spur tremendous growth in the renewable energy sector and ecological economy in general, as public consciousness opens up to these ideas on a large scale.

I want to keep giving quotes, but you can read it. (If anyone is out of free articles for New Yorker, I can send a text file.) I’ll contribute a few of my own thoughts, expanding on stuff implicit in the article; and then this topic can be continued with another post.

…..

Divesting is a truly powerful lever, for several reasons.

First, money talks. Many people who have been misled by modern society have the following equation in their heads:

money = value

These people, being overwhelmed with social complexity, have lifted the “burden” of large-scale ethics off of their shoulders and into a blind faith in the economic system – thinking “well, if enough people have the right idea, then capitalism will surely head in the right direction.”

Of course, after not too long, we find that this is not the case. But their thinking has not changed, and we need a way to communicate with them. While it may feel strange and wrong to reformulate the message from “ethical imperative” to “financial risk”, this is the way to get through to many people in powerful places. When you read about success stories, it is effective, especially considering all the time spent mired in anthropogenic-warming skepticism.

Second, social pressure is now a real force in the world. We can bend competition to our will: incentivize companies to better practices, and when one capitulates, the others in that sphere follow. It has happened many times, and the current is only getting stronger.

Though if we want to fry bigger fish than no-straws, we need to sharpen our collective tactics. It will of course be more systematic and penetrating than shaming companies on Twitter. The article includes great examples of this; it would be awesome to discuss more ideas in the comments.

Third, everyone can help this way, directly and significantly. Everyone has a bank account. It is not difficult, nor seriously detrimental, to switch to a credit union. The divestment campaign can be significantly accelerated by a movement of concerned citizens making this transition.

(My family uses Chase. When I was spending quality time back home, I asked my parents how the value of a bank is anything more than secure money storage. The main thing they mentioned was loans – but they admitted that the biggest and best loan they ever took was through a credit union. The reasons simply did not add up. I plan to show them this article, and I’ll try to have an earnest conversation with them. I really hope they understand, because I know they are rational and good people.)

It’s all but impossible for most of us to stop using fossil fuels immediately, especially since, in many places, the fossil-fuel and utility industries have made it difficult and expensive to install solar panels on your roof. But it’s both simple and powerful to switch your bank account: local credit unions and small-town banks are unlikely to be invested in fossil fuels, and Beneficial State Bank and Amalgamated Bank bring fossil-free services to the West and East Coasts, respectively, while Aspiration Bank offers them online. (And they’re all connected to A.T.M.s.)


This all could, in fact, become one of the final great campaigns of the climate movement—a way to focus the concerted power of any person, city, and institution with a bank account, a retirement fund, or an insurance policy on the handful of institutions that could actually change the game. We are indeed in a climate moment—people’s fear is turning into anger, and that anger could turn fast and hard on the financiers. If it did, it wouldn’t end the climate crisis: we still have to pass the laws that would actually cut the emissions, and build out the wind farms and solar panels. Financial institutions can help with that work, but their main usefulness lies in helping to break the power of the fossil-fuel companies.

…..

The economy is far more responsive to changes in the collective ethos than the government. This is how people can directly express their values every day, with every bit of earning they have. We are recognizing that the public mindset is changing, and we can now take heart and leverage society in the right direction.

Conjecture The critical science of our time has the form:

Ecology
\Uparrow \;\;\;\;\; \Downarrow
Economy

This is why John Baez brought together so many capable people for the Azimuth Project. I hope that we can connect with the new momentum and coordinate on something great. Even in just the last post there were some really good ideas. I really look forward to hearing more. Thanks.


UN Climate Action Summit

4 September, 2019

Christian Williams

Hello, I’m Christian Williams. I study category theory with John Baez at UC Riverside. I’ve written two posts on Azimuth about promising distributed computing endeavors. I believe in the power of applied theory – that’s why I left my life in Texas just to work with John. But lately I’ve begun to wonder if these great ideas will help the world quickly enough.

I want to discuss the big picture, and John has kindly granted me this platform with such a diverse, intelligent, and caring audience. This will be a learning process. All thoughts are welcome. Thanks for reading.

(Greta Thunberg, coming to help us wake up.)

…..
I am the master of my fate,
      I am the captain of my soul.

It’s important to be positive. Humanity now has a global organization called the United Nations. Just a few years ago, members signed an amazing treaty called The Paris Agreement. The parties and signatories:

… basically everyone.

By ratifying this document, the nations of the world agreed to act to keep global warming below 2C above pre-industrial levels – an unparalleled environmental consensus. (On Azimuth, in 2015.) It’s not mandatory, and to me that’s not the point. Together we formally recognize the crisis and express the intent to turn it around.

Except… we really don’t have much time.

We are consistently finding that the ecological crisis is of a greater magnitude and urgency than we thought. The report that finally slapped me awake is the IPCC 2018, which explains the difference between 2C and 1.5C in terms of total devastation and lives, and states definitively:

We must reduce global carbon emissions by 45% by 2030, and by 100% by 2050 to keep within 1.5C. We must have strong negative emissions into the next century. We must go well beyond our agreement, now.

(Blue is essentially, “we might still have a stable society”.)

So… how is our progress on the agreement? That is complicated, and a whole analysis is yet to be done. Here is the UN progress tracker. Here is an NRDC summary. Some countries are taking significant action, but most are not yet doing enough. Let that sink in.

However, the picture is much deeper than only national. Reform sparks at all levels of society: a US politician wanting to leave the agreement emboldened us to form the vast coalition We Are Still In. There are many initiatives like this, hundreds of millions of people rising to the challenge. A small selection:

City and State Levels
Mayors National Climate Action Agenda, U.S. Climate Alliance
Covenant of Mayors for Climate & Energy
International Levels
Reducing emissions from deforestation and forest degradation (REDD)

RE100, Under2 Coalition (The Climate Group)
Everyone Levels
Fridays for Future, Sunrise Movement, Extinction Rebellion
350.org, Climate Reality

Each of us must face this challenge, in their own way.

…..

Responding to the findings of the IPCC, the UN is meeting in New York on September 23, with even higher ambitions and higher stakes: UN Climate Action Summit 2019. The leaders will not sit around and give pep talks. They are developing plans which will describe how to transform society.

On the national level, we must make concrete, compulsory commitments. If they do not soon then we must demand louder, or take their place. The same week as the summit, there will be a global climate strike. It is crucial that all generations join the youth in these demonstrations.

We must change how the world works. We have reached global awareness, and we have reached an ethical imperative.

Please listen to an inspiring activist share her lucid thoughts.

Carbon Offsets

15 August, 2019

A friend asks:

A quick question: if somebody wants to donate money to reduce his or her carbon footprint, which org(s) would you recommend that he or she donate to?

Do you have a good answer to this? I don’t want answers that deny the premise. We’re assuming someone wants to donate money to reduce his or her carbon footprint, and choosing an organization based on this. We’re not comparing this against other activities, like cutting personal carbon emissions or voting for politicians who want to cut carbon emissions.

Here’s my best answer so far:

The Gold Standard Foundation is one organization that tackles my friend’s question. See for example:

• Gold Standard, Offset your emissions.

Here they list various ways to offset your carbon emissions, currently with prices between $11 and $18 per tonne.

The Gold Standard Foundation is a non-profit foundation headquartered in Geneva that tries to ensure that carbon credits are real and verifiable and that projects make measurable contributions to sustainable development.