There are so many factors driving the climate crisis, but it’s not always clear what matters most. I briefly outlined the top 4 causes in my open letter, and I’ve invited Oli Hall to take a closer look at one of them for the Target 2030 readers.

Oli is a data engineer and truly dedicated to fighting the climate crisis. Currently he’s undertaking a years sabbatical to help work on solutions to combat the crisis. He’s been collecting a vast array of resources on and publishes an outstanding newsletter that I’d highly recommend you sign up to (Oli didn’t ask me to promo it, I just can’t help myself, it’s amazing!):


Forge The Future

Fight hope in the face of the climate crisis.

Okay, now the intro is out of the way, over to Oli…


If you’re reading this, it’s likely you’re aware that the planet is warming rapidly.

You’ve probably also heard that much of this warming is due to man-made (anthropogenic) greenhouse gas emissions that accelerate the greenhouse effect, trapping heat in our atmosphere. But when it comes to how much CO₂ is being emitted, and from where, it’s a lot harder to get clear answers.

Everyone likely knows at least one major source of emissions – coal power, cars, flying, or perhaps eating meat. But which is the most significant?

Different Gases, Same Effect

Let’s start with the basics – what counts as a greenhouse gas (GHG)? GHGs are any gases that trap heat within our atmosphere. CO₂ is the most well known of these – we breathe it out, and it’s emitted from most internal combustion engines, power plants and much more.

However, there’s also a selection of others:

  • Methane – produced from ruminants (cows, sheep) as well as through some geological processes
  • HFCs – used in refrigerators and air-conditioning units as a replacement for the ozone-destroying CFCs that were largely banned in the 1970s
  • SF6 – used as an insulator in electrical switchgear
  • and many more

Some of these gases are much more effective than others at trapping heat in the atmosphere. SF6, for example, is 23,500 times more effective than CO₂ at trapping heat over a 100 year period! That said, given the sheer volume of CO₂ emissions, this is often cited as our primary concern, and they will be the focus of data sourced for this article.

Often, these different gases are converted to CO₂ equivalents (sometimes referred to as CO₂-e) for ease of comparison.

Emissions By Country

Right, onto the numbers. Overall, globally we emit around 37,000,000,000 tonnes of CO₂ per year. This is clearly a vast number, so let’s slice it up in different ways.

First, we’ll look at how much each country produces:

In absolute, per-country terms, emissions are dominated by China and the US.

However, China has over 1 billion residents, whereas the US has around one quarter of their population. How do things look if we look on a per-person level?

Wow, that’s quite a difference! Suddenly, North America, Australia and Saudi Arabia shoot to the top, with China relatively middling in comparison.

However, as a species, we’ve been emitting CO₂ in large volumes since the Industrial Revolution. So what happens if we look at cumulative emissions over time?

The picture shifts again – now the EU dominates the picture, alongside the US, with China barely a scratch on the surface.

My point with all these graphs is not only to show the scale of the problem, but that it is a collective responsibility. Depending upon how one slices the data, it’s possible to lay the blame at any major nations’ feet.

Right, so we now know a bit more about where it comes from – now let’s look at what emits all this CO₂.

Emissions By Sector

If we look at CO₂ by sector, we can start to see how things break down. Most of the CO₂ produced globally by humans is for energy, as we might expect – it takes a lot of power to keep the world running, and that amount is growing over time, as efficiency gains in developed countries are outweighed by developing countries, well, developing!

Luckily, this is one sector where things are starting to change – despite the entrenched interests of the fossil fuel industry, plus the inherent simplicity of burning coal or oil, renewable energy is growing rapidly year on year, whilst the most polluting fuels (coal) are becoming less and less economically viable. However, at the moment, we’re still only at the stage of renewables absorbing new energy usage, rather than replacing existing power demand.

Next up is transport, covering everything from cars, and trucks, to buses, trains, ships and aircraft. This sector is a big one, and steadily growing – there’s always more demand for transport, from the personal scale all the way up to international freight.

There have been some efficiency gains here and there, but they’ve been eaten up by increased demand. Promising new technologies like EVs and hydrogen fuel cells offer low/zero emission alternatives to current internal combustion engines, but adoption is still relatively low (although China’s massive policy push in this direction is helping). Some types of transport such as aviation have no immediate low-emission alternative, so this sector is likely to continue to rise unless some way is found to curb demand.

After transport come land use and agriculture. Whilst distinct, they’re closely linked.

Land use deals with changing land use – land being forested or deforested, or farmland being created. Whilst it’s often a one-time operation (for any given piece of land), the impacts are visible on a global scale, due to the extent of the land use changes, and the types of change.

I’m sure most of you will be aware of the benefits trees have on CO₂ levels – they act as carbon sinks, sucking up CO₂ and storing it. Naturally, therefore, if you cut down the trees and burn them, as is often done when forests are cleared, all that carbon is released. The clearing of different landscapes can have varying impacts – burning tropical rainforest is particularly intensive, as is clearing mangrove swamps and peatland.

One major reason that people clear land is for farming. Humans have to eat, after all, and agriculture takes up over a third of all land area, and is host to a number of significant emissions sources, from nitrate emissions from overuse of fertilisers (excluding other effects from agricultural run-off) to methane emissions from ruminant animals grown for milk and meat. There’s always pressure for more farmland, and unsustainable farming techniques can result in soil becoming degraded, meaning farmers are under constant pressure to move on, threatening natural ecosystems.

The last two significant sectors are residential and commercial, and industry. The first is the CO₂ released from our daily lives – usually this comes in the form of fuel burnt for heat and/or power at a residence or business, rather than pulled from the main grid. In developed economies, this tends to be less of a factor, but in developing countries, this can be a significant source of emissions.

Emissions from industry are dominated by a couple of key industries – steel and concrete. Both are driven by construction, and both are heavy emitters. Concrete releases CO₂ as an inherent part of the chemical production process, and making steel involves removing carbon-based impurities from iron. There are emerging alternatives that emit lower (and negative) CO₂, but these technologies are very much in their infancy, and takeup is thus far negligible.


So there you have it – a whistle-stop tour of the principal sources of CO₂ and some of the background on GHG emissions more broadly. As always with a topic this broad, there’s a huge amount of complexity and nuance in all of these areas – we’re dealing with a process on a global scale after all – so I’d encourage you to dive in further and investigate yourself. This post was heavily influenced by Our World in Data’s excellent post on the same topic and I’d recommend it for a deeper dive. They were also the source for the visualisations used throughout.

I’ve mostly avoided talking about solutions here, not because we don’t have them – far from it – but because the task of tackling global warming is a long and complex one.

Is it achievable? Absolutely, but the route we take will be a complex and winding one, especially given the level of political wrangling required at an international scale. All we can do as individuals is to try and limit our own impact (you’re in the right place to learn about how!), and lobby our political representatives, whoever they are, to take this seriously.

Help Target 2030 to capture greenhouse gas emissions

Become A Donor

© Target 2030, 2019.