The world has a carbon budget for 2030 and 2050, as do nations in their Nationally Determined Contributions submissions that are part of the Paris Agreement. Individuals do not, and they vary widely; the average per capita consumption emissions for an American are about 17.6 tonnes per year, while an average Indian emits only 1.7 tonnes.

Meanwhile, the richest one percent of the world may have an annual footprint as high as 75 tonnes of “lifestyle” emissions, or those emissions directly attributable to what we as individuals do and how we live. Max Roser of Our World in Data points out that half the world is emitting far too much carbon, but that the other half suffers from energy poverty: “Those that do not have sufficient access to modern energy sources suffer poor living conditions as a result.”

Any fair and equitable division of the carbon budget has to allow headroom for those suffering from energy poverty to get a little more of it. At the other end of the spectrum, when I fly to Portugal or drive my Subaru, I may get the benefit and pay the cost in dollars, but everyone in the world is affected by the carbon emissions. So a logical, equitable, and reasonable place to start is with an average carbon budget for everyone on the planet.

Lifestyle emissions are not just individual but the things that we share a piece of, from how we organize our society and our institutions. They are a big chunk of global emissions; a 2009 study concluded that “on the global level, 72% of greenhouse gas emissions are related to household consumption, 10% to government consumption, and 18% to investments.”

The next bit of math is also straightforward; we have a carbon emissions budget target of 25 gigatonnes in 2030 to stay under 1.5 degrees of warming. If you divide that by the world’s population, the result is roughly 3.4 tonnes per person per year. Multiply that by 72% and you get a 2030 target lifestyle footprint of 2.5 tonnes of CO2e per person per year. That’s the 1.5-degree lifestyle.

Many will argue that expecting someone in the United States to lower their consumption to a worldwide average is crazy socialist talk, and that it will never happen. They are probably right, but it is a place to start. After all, we are not talking about money or status here, we are talking about carbon. The rich man can park his Tesla under his Tesla Solar Roof and charge his Tesla battery and have a very expensive but low operating carbon lifestyle. And frankly, it is not an unrealistic or unreasonable target.

I learned of the actual term “1.5-degree lifestyle” from Rosalind Readhead, who pointed me to a study from the Institute for Global Environmental Studies (IGES), Aalto University, and D-mat titled 1.5-­Degree Lifestyles: Targets and Options for Reducing Lifestyle Footprints. It provided the fundamental underpinning of this project; as noted in the introduction:

Lifestyles of individuals consist of various elements of daily living including consumption relating to nutrition, housing, mobility, consumer goods, leisure, and services. The consumption based accounting adopted in this study attributes GHG emissions at production stages as indirect emissions caused by household consumption. This provides a different angle from the footprint of specific products, organizations, cities, or countries, which have been the foci of most footprint studies so far.

The lifestyle study authors acknowledge that this cannot be achieved by individuals on their own; much of it is structural and locked-in. Our world is designed around consumption of energy, and it is hard to break this pattern.

Although this study quantifies impacts of GHG emissions from the perspective of lifestyles and consumption by households, it does not mean that individual households are solely responsible for reducing the footprints. The sheer magnitude of change required for a shift towards 1.5-degree lifestyles can only be achieved through a combination of system-wide changes and a groundswell of actions from individuals and households.

So much of our consumption is “baked-in” to the way our economies are set up; we still need political action and societal change. But that doesn’t give us carte blanche to blame the system and not take personal responsibility.

The 1.5-degree lifestyle report studied people’s lives in great detail in four countries, looking at six “lifestyle domains”: nutrition, housing, mobility, consumer goods, leisure, and services. After studying the results in all six sectors, the authors concluded that about 75% of the impact fell within the hotspots of nutrition, housing, and mobility, basically what we eat, where we live, and how we get around.

I was not convinced of this; in my own situation, I have found that “communication and information” in the services category are in fact one of my biggest sources of emissions because I spend all day on my computer connected to the internet. My consumption of expensive Apple consumer goods turns out to eat up a lot of my carbon budget too, so we will look at all six sectors, not just the hotspots.

The divisions are also somewhat arbitrary. It is also not so simple to think of them as six separate categories. I will show that housing and transportation are two sides of the same coin and that nutrition is affected by both, as are consumer goods. The North American family tends to drive an SUV to the big-box store once a week for groceries, putting much of them in a giant fridge. The urban Italian might have a tiny fridge, picking up the fresh fixings for dinner on the way home. The Japanese worker might get off the subway and find themselves surrounded by vast multi-level supermarkets. They don’t buy the giant tub of ice cream; it’s heavy, it might melt, and they don’t have a freezer big enough for it. So dividing everything into six lifestyle domains is not really accurate; it’s all connected and interrelated, and it is all a rough approximation. However, the six lifestyle domains are a good place to start, a way to break things down into measurable categories.

The study authors describe three approaches we can take in each category to reduce our footprints, an extremely useful division.

Absolute Reduction

Absolute reduction “means reducing physical amounts of goods or services consumed, such as food, kilometers driven, energy use, or living space, as well as avoiding unsustainable options.” Simply put, just using less. This is the “less is more” and “living with less” approach that I have called sufficiency, asking the question, How much do we really need?

Efficiency Improvement

Efficiency improvement “means decreasing emissions by replacing technologies with lower-carbon ones while not changing the amount consumed or used, such as in energy-efficient agriculture, vehicles, or housing.” This has always been the standard approach, improving the efficiency of everything that we make and use. But it has failed us: as cars got more efficient, they turned into SUVs; as houses got more efficient, they got bigger.

Modal Shift

Modal shift “means changing from one consumption mode to a less carbon intensive one, such as in adopting plant-based diets, using public transport, or renewable energy for electricity or heating.” This is perhaps the most interesting and important approach: doing things differently. Like absolute reduction, it is closely related to the concept of sufficiency: why drive a car when you can ride a bike, or why use a dryer when you can string a clothesline? Modal shifts also give us the greatest carbon emission reductions and the greatest opportunities.