During the last few months, I have taken more time again to attend events organised by environmental groups and civil society organisations. One particular point of discussion surfaces as frequent as it did when I started getting active in sustainability five years ago. At one side, you have those who believe we can meaningfully reduce emissions by individual lifestyle changes. At the other side are those who believe such efforts are futile, pointing fingers to pollution created by the ‘big companies’.

Even though I’ve always agreed that the climate crisis is a systemic problem that needs a systemic solution, I am a strong believer in taking personal action. I have my reasons. First, these big companies wouldn’t be big wouldn’t it be for us consuming their products. Second, nobody will take you seriously if you don’t at least do an effort to reduce your own impact before demanding action that will affect others. One should put their money, time, and energy where their mouth is. Third, in the midst of political institutions failing to address the climate crisis, it feels great to do something tangible – no matter how small the impact really is.

Yet, many people who don’t have the passion or the time to study climate science and carbon footprints, probably feel hopelessly lost. Should I stop driving a car? No more plastic bags? Can I still go on holiday? Can I not eat meat anymore? The confusion is understandable if you see the staggering amount of disinformation spread on social media – not seldom by organisations that claim to fight for the environmental cause. In fact, the terms environment and climate are often used interchangeably, while they mean different things.

Looking at actions to reduce the climate crisis, it mostly (yet, not entirely) comes down to reducing greenhouse gases to avoid further acceleration of global temperature rise. Articles promising the ‘top 5 measures to reduce your footprint’ look tempting and might give some idea of where society should generally focus one’s attention, but often fall flat when it comes to the applicability to the reader in question. Indeed, suggestions ranking dietary changes and transport modes are based on average footprints. If you really want to know what to do, you should grab pen and paper, open up Google, and get ready for some (easy) maths.

The three dimensions of personal budgeting

Ever since I built my travel carbon footprint calculator a couple of years back, I have been intrigued by the idea of doing personal accounting beyond the monetary dimension. Indeed, most people book holidays and trips with their budget as most important constraint. When multiple modes of transport are possible, like plane versus train, the time difference of the journey is brought into the equation. Depending on a person’s budget and time constraints, the financial and time dimension are weighted against one another.

Once you add the carbon intensity of the transportation mode into the mix, you have a complex act of balance to respect three budgets: carbon, time, and money. This exercise will look different from person to person and is likely to change over time. For example, when I started out doing my budgeting among these three dimensions, about 4 years ago, I was still a student. My monetary dimension was pretty constraint, but I was more flexible with my time (especially in the long summer holidays). At the same time, I set myself a budget of about 800 kg CO2 per year for travelling – the equivalent of a one-way flight from Brussels to New York. As a result, I often ended up taking 15+ hour Flixbus trips, all around Europe. Once I started working, my financial means became more relaxed, but vacation days became more stringent. So, I started taking the much faster, but also much more expensive, international trains that cross Europe. I also decided several times to skip a reunion or event abroad altogether because it didn’t fit in my carbon, time, and financial budget.

You might wonder where the 800 kg carbon budget comes from. Setting my personal carbon budget is a combination of realism (one European city trip by plane would easily use up half of my yearly budget) and ambition (to avoid spending more carbon on a luxury like travel than on my (mostly plant based) diet of about 1.2 tonnes of CO2 per year). An important number to always keep in mind is that each person on this planet currently has a yearly carbon budget of 2 tonnes, which needs to be gradually reduced to zero by 2050 to maintain a reasonable chance of limiting global temperature rise to 1.5 degrees celcius by the end of this century. Currently, people in the west far overshoot this carbon budget.

It took me some research to establish and evaluate my personal goals and if you really want to figure out how to effectively reduce your emissions, you’ll need to get ready for some desk research yourself. In what follows, I describe some ways of going about his. We’ll see how to identify in which part of your life you might want to focus your actions. Afterwards, we’ll see how we can assess the financial and time cost of cutting carbon by specific lifestyle changes. Important to keep in mind that I do these example calculations based on data for an average Flemish person. You can use the same methodology but use data applicable to your situation. I admit, it might all sound a bit nerdy, but I promise it’s worth a closer look!

Incremental changes versus big wins

As we will discover, some emission reduction strategies allow you to take incremental (and often easier) steps towards a lower carbon footprint. For example, decarbonising your diet can go in small steps: you don’t have to go vegan overnight. Come the next meal, you have the choice to align with a new diet type or go for what you’re used to. In the course of one year, you face that decision more than a thousand times and you can make a transition at the pace you want and suits your budget. In contrast, the decision to go on holidays by train instead of plane presents itself far less frequent, and will probably also have a higher financial impact at a time.

Against this background, it is wise to have a general idea how all your emissions add up on a yearly basis. Which areas contribute a lot to your overall footprint? And which areas allow for incremental changes, which ones allow onetime big wins?

Below I listed the typical carbon budget of an average Flemish person broken down in general categories of activities and spending. I base myself on data of the Flemish Institute for Research and Innovation (VITO) and the Flemish Environmental Bureau (VMM). Turns out an average person in Flanders has a footprint of about 20 tonnes of CO2 per year – one of the highest levels in the world! This footprint also includes emissions caused abroad during the production of imported goods and services (including fuels). That’s important, because emission abroad account for about half a Flemish person’s footprint. Remarkable as well is that about 6 tonnes of yearly emissions per Flemish capita are linked to governmental activities and infrastructure like schools, hospitals, and the army. I didn’t include this category in the table though, because a person cannot immediately affect these activities. In the last column of the table, I indicated how often a person can act upon his or her lifestyle in each category.

Emissions categoryYearly EmissionsShare in carbon budget one has a direct impact on (rounded to add to 100%)Frequency of decision/yearDecision impact (maximum impact on yearly emissions/decision)
Diet2.8 tonnes, of which 45% due to meat, fish and dairy22.0%11000.02 % / decision
Daily commuting2.5 tonnes, of which 90% is due to using a car to go to work19.7%220-3000.08 % /decision
Energy consumption in the house4.4 tonnes, of which 75% is heating and 25% is electricity consumption34.6%<234.6 % / decision
Travel (transport only)0.4 tonnes3.2%<51.6 % / decision
Other goods and services bought2.6 tonnes20.5%>10000.02 % / decision
Total emissions on which one has a direct impact12.7 tonnes100%

Looking at this table, the average Flemish person should focus on how he or she heats and electrifies his or her house – if they want to have a big impact. Changing your energy supplier is quite easy nowadays and doesn’t cost much time, but swapping out the gasoline or gas boiler for an electric edition is not only a big undertaking, it is also very expensive to heat your house electrically in Belgium. Therefore, for many people little change can be made in this category in the short term.

More attainable, and therefore my favourite recommendation to people wondering how to reduce their environmental impact, is to focus on the travel category. Since most people only make one or two bigger trips per year, they only have to decide once or twice to ditch the plane. Once one made that mental switch, you’ll discover you can have a great vacation close to home as well. The impact of this one decision is quite big and can save immediately half a tonne up to several tonnes if you take several flights a year. Keep in mind that the table above represents the average Flemish person and the data includes children, elderly, and people with weaker economic status.

On the other end of the spectrum, deciding to eat vegetarian on your next date will barely make a dent in your carbon emissions. To have a larger impact, one needs to switch to a vegetarian or vegan diet for the majority of its meals. For many people, this is a daunting idea, since it very much affects their daily routine. Up to you to decide where to direct your efforts!

Carbon Abatement Costs

Once you have a rough idea how your overall carbon footprint is caused by different activities and lifestyle choices, it is time to have a look what you can do about it. Most people sincerely want to reduce their carbon impact, but are also cautious about their finances and their time. That’s why I want to explore the use of marginal abatement costs (and times) for personal carbon budgeting. Working with marginal carbon abatement is not a new concept. Consultancy firm McKinsey introduced a ranking of such abatement costs in their Marginal Abatement Cost Curve (MACC) in 2007 to inform policy makers where to direct funds for maximal CO2 reduction impact and has updated it a few times since then. I thought, ‘if politicians can use it, I can so too!’. The Marginal Abatement Cost (MAC) expresses how much it costs to avoid emitting a tonne of CO2 using a certain carbon reduction policy or technology. An example of the McKinsey MACC is shown below.

The Marginal Abatement Cost Curve as originally worked out by consultancy firm McKinsey to inform policy makers (source: McKinsey)

So… how to calculate the Marginal Abatement Cost (MAC)? It’s very simple!

MAC = cost of implementing the measure / saved CO2 emissions [€/kgCO2]

Note that both the cost and the amount of saved emissions of a certain measure are determined by comparing them with the status-quo, also called the baseline. For example, imagine a government that wants to stimulate the uptake of electric vehicles and has determined that consumers need a subsidy of 5000 euros to be convinced to make the switch from a diesel or gasoline car. In a country like the Netherlands, an electric vehicle that drives 200 000 kilometers over its lifetime, might save about 50 tonnes of CO2 (taking the whole lifecyle into account, source). It will hence cost the government about 500 euros per tonne CO2 avoided. Up to the government to compare that with other measures and wheigh their options.

The MAC is, of course, not telling the whole story. Most carbon mitigation measures and technologies have other, often unquantifiable, benefits. Turns out the abatement curve of McKinsey is controversial because of quite some erroneous assumptions. They also forgot to take into account the loss of taxes by implementing certain measures, hence miscalculating their true cost for society.

Luckily, for personal use, the MAC can be used as a rule of thumb if you want most carbon savings for your buck. For those worried about the time investment linked to adopting a new lifestyle, we can equally define the Marginal Abatement Time (MAT):

MAT = time investment to implement the measure / saved CO2 emissions [h/kgCO2]

Again, we are comparing to the status-quo situation here. Note that when the MAC or MAT has a negative value, one saves money or time respectively. Indeed, an eco-friendly lifestyle doesn’t always have to cost money or be cumbersome!

Time for a practical example

Let’s make things a bit more concrete with a practical example. As I mentioned in the introduction, I started my three-dimensional budgeting act in the travel department of my emissions. For many people, this is an easy way to start, because it is pretty easy to find reliable figures on the carbon emissions related to different modes of transport. You also don’t have to completely change your daily routine, as is the case with some of the other carbon reduction measures.

Imagine I am getting bored of the rainy weather here in Brussels and decide to make a city trip to sunnier Barcelona. If I wouldn’t be the climate geek I am today, I would probably just book a Ryanair flight in a few clicks. What is the MAC and MAT of the alternatives by bus and train? An overview of the assumptions below for a return trip, based on experience and my carbon calculator.

ScenarioFinancial costCarbon costTime cost
Plane (baseline, status-quo)€ 60410 kg CO2eq10 hours
Train€ 20060 kg CO2eq24 hours
Bus€ 4044 kg CO2eq40 hours

Based on these assumptions, we calculate the MAC and MAT for the train and bus scenarios. The result is shown in the table below. To make them comparable with abatement costs in literature, I expressed them in euros per tonne CO2eq saved.

Train400 €/tonne CO2eq40 h/tonne CO2eq
Bus– 55 €/tonne CO2eq82 h/tonne CO2eq

Note that the MAC of taking the bus is negative. You are actually saving money while reducing your emissions! When you want carbon reductions for your buck, this is the way to go. If you are very conscious about the number of vacation days you have, the MAT is an important measure to keep in mind and the train might be a better option for you.

The elephant in the room here is the fact that I could cancel out on my trip to Barcelona altogether. If I would do a staycation instead, I find a negative MAC of about – 146 €/tonne CO2eq. I am saving money while saving emissions. Does one have to conclude that it’s better to not travel abroad anymore altogether? Not per se! It all comes down to what I would do with the money and time you save by not taking the plane! If I spent that at home on carbon intensive goods and services, my good deed could be (partially) undone.

For luxury expenses, like travel, not going is an option to consider. But when making choices about one’s diet, the commute to work, your electricity supplier, not consuming is not option. You can’t stop eating, stop showing up at work, or stop using electrical appliances. Yes, we can reduce our consumption in many areas of our lives, but the question remains how to reduce the impact of the remainder.

Building a Marginal Abatement Cost Curve

Let’s see if we can expand above’s analysis to the MAC in different categories of our emissions. Where relevant, I also calculate the MAT. Each time, I define a baseline scenario and a number of alternatives. This is again based on data for an average Flemish person. At the bottom of this article, you find the tables showing the individual results per carbon reduction measure and some of the main assumptions.

Let’s call our study object Bob. Bob is living about 20 km from his work, normally commutes by car, makes on city trip every year by plane, and has a typical Flemish diet rich in meat and dairy products. He lives in a 70 square meter apartment that is rather old and is heated by a gas boiler.

In total, I evaluated 11 lifestyle changes for Bob, over the first four categories of the carbon footprint overview we saw earlier (diet, heating & electricity, commuting, and travel). The resulting Marginal Abatement Cost Curve is shown below (click on it to enlarge). Note that the height of the bars represent the abatement cost, while their width represents the abatement potential on a yearly basis.


An example of a personalised MACC for Bob, using data of an average Flemish person (source: author)

Careful, some of the measures have overlapping effects. For example, once you take the bike to work, having a carbon reduction potential of about 2,5 tonnes CO2 per year, you can’t count on the reduction potential of taking the train to work. You cannot simply add up the carbon abatement potential of different actions.

Don’t forget the Rebound Effect!

When crunching the numbers on your own MACs, MATs, and MACCs, it is very important to keep one thing in mind: do not forget the opportunity costs (or wins)! If you decide to travel by train from now on, the money you additionally spend on train tickets cannot be spent on something else. If this alters your consumption pattern elsewhere, the carbon impact of that change needs to be accounted for as well. Vice versa, measures that save not only carbon but also money, might lead to spending that money on more stuff (new phone, TV, etc) which increases your carbon footprint again. This effect is known as the rebound effect and is a common phenomenon among people saving fuel or electricity.

If you really want to make sure you make the optimal decisions within a constrained budget of money, time, and carbon, there is nothing else you can do than set up an optimisation algorithm that figures out exactly the optimum point to spend your time and money for minimal impact. If a large amount of people would start optimising their lifestyle like this, the effect would become noticable in the market. Demand for polluting goods would initially start to fall, hence prices drop, after which (other) people might start bying more of it. Modeling the demand-supply interactions in the national and global economy is a whole other undertaking though. Yet, for personal use and with a bit of common sense, one can apply above approaches sensibly.


When I started writing this blog post, I didn’t know where I would end up. Once more I discovered that evaluating the carbon impact of lifestyle changes is so damn tricky. Everything stands and falls with your assumptions, the availability of data that reflects your own situation, and the danger to fall in the trap of the Rebound Effect. Nonetheless, we have shown which data to look for and how to organise it. I hope you can now figure out which area of your life you can focus on for incremental change (diet, commuting, buying decisions) and which ones to focus on for big impact (energy for heating and electrifying your house, travel). We also translated the Marginal Abatement Cost Curve, well known in policymaking, to personal lifestyle changes.

All with all, most of the results are pretty much in line with common sense observations. I would therefore argue that the process, looking up data and educating yourself about the impact of different daily activities, is more valuable than the calculations itself. Doesn’t take away that it can be a lot of fun to geek out a little bit every now and then!

Extra: results and assumptions

In this section, I list some of the intermediate results to obtain the Marginal Abatement Cost Curve for Bob. I also indicate some of the main assumptions. Keep in mind that, even if you happen to live in Flanders just like Bob, your situation and hence your MACs might look totally different!

ScenarioFinancial cost


Carbon cost

[kg CO2/meal]


[€/tonne CO2eq]

Meat based diet (baseline, status-quo)52.6
Vegetarian4.51.5– 455

Assumptions: baseline diet is the average Flemish diet, rich in meat, fish and dairy. Vegetarian diet is considered 10% cheaper, vegan diet 10% more expensive. Carbon reduction potential based on Shrinkthatfootprint and others.

Daily commute
ScenarioFinancial cost [€/100 km]Carbon cost [kg CO2/100km]Time cost [h/100km]MAC [€/tonne CO2eq]MAT [h/tonne CO2eq]
Driving to work gasoline car (baseline, status-quo)24201.43
Driving electric1871.43– 4620
Taking the train occasionally183.52.5– 3640.6
Taking the train always103.52.5-8480.6
Biking0.505– 1175178.5

Assumptions: Bob owns an average sized car with emissions of 200 grams CO2/km (full lifecycle). Electric car charging at home at average Belgian electricity mix, full lifecycle emissions also taken into account. Linear depreciation taken into account for car ownership, assuming 200 000 km over lifetime. Trains driving on Belgian electricity mix. Assuming a train abonnement cost divided over yearly commute with 220 working days. Bob lives 20 km from work and 15 min walking from the train station.

Heating & electricity in the house

Financial cost


Carbon cost

[kg CO2/year]


[€/tonne CO2eq]

Heating & sanitary water on gas, grey electricity contract (baseline, status-quo)

1050 + 88 + 300 = 1438

4830 + 300 + 227 = 5357

Switch to 100% renewable energy supplier




Electric boiler for heating & sanitary

2916 + 245 + 300 = 3461

2205 +140 + 227 = 2572


Electric boiler + 100% renewable supplier




Assumptions:  70 square meter apartment, not newly built with heating requirement of 150 kWh/m2/year. Electricity consumption is 1200 kWh/year. Electricity cost is 0.25 €/kWh in grey contract, gas cost is 0.05 €/kWh. Assuming grey electricity contract in baseline, having footprint of average Belgian electricity mix. Assuming hot water consumption of 20 000 liter per year. Assuming electric boiler efficiency of 90%, gas boiler 50%.