Net-zero cannot be achieved by planting a few trees or keeping lights switched off more

How much of the world’s emissions are down to aviation?

How much of the greenhouse gases being pumped into the atmosphere are coming from our homes, whether in the form of the electricity we use or the gas that goes in our boilers?

What about deforestation, or agriculture, or manufacturing?

These questions are worth pondering because it turns out the answers are actually rather surprising.

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Indeed, there is a serious disconnect between the stuff you often see depicted on screens and in newspapers to symbolise the environmental movement, and what the data actually tells you about the realities of carbon emissions.

Did you know, for instance, that we create far, far more greenhouse gas emissions through the manufacture of cement than the entire total emissions from the aviation industry?

Cement is responsible for a double-whammy of carbon emissions: first, through the chemical reaction you need to carry out to turn limestone into lime and then, on top of that, further carbon emissions attributed to the fossil fuels that power the cement kilns themselves.

Put those two together (each is roughly 3-4%) and cement accounts for anywhere between 6 and 8% of global emissions – that’s more than the entire combined emissions of every plane in the sky, every train on a track and every ship in the ocean.

Yet given cement is one of the key building blocks in, well, buildings, primarily as a crucial ingredient in concrete, we cannot simply stop making it.

Or consider another example.

Consider the billions of homes around the world where we all live: they are responsible for about 10.9% of total global carbon emissions.

That’s everything from electricity which comes from fossil fuel power stations to coal and wood burnt at home to gas in boilers.

However, the combined emissions of the iron/steel industry and chemical sector are similar or greater, depending on what you’re including (10.8% if you only consider the energy powering these plants, a whopping 13% if you include the emissions puffed into the sky from chemical plants).

On the one hand, nearly eight billion people; on the other, a few thousand plants.

These calculations matter, because whatever you think about the wisdom of reducing greenhouse gas emissions to zero, the fact is that the government here in the UK has committed to doing precisely that by 2050, as have most other developed nations.

Today Joe Biden took a step in that direction by aiming to cut US emissions by more than 50% compared with 2005 levels by 2030.

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If we are going to eliminate those emissions we need to understand where they’re coming from: which countries and indeed which processes.

In some cases, the answer is the same.

China produces comfortably the most greenhouse gas emissions in the world and it also produces the most steel and the most cement.

However, other emissions come from somewhat unexpected places.

For instance, a full 1.3% of the world’s emissions comes from rice farming.

In the case of rice farming, this is more about methane emissions than carbon since bacteria in the waterlogged paddy fields used for growing rice tend to emit a lot of greenhouse gas.

This is nonetheless about the same contribution to global carbon emissions as every other crop in the world, combined.

In some cases, we already know what to do about these emissions.

Around the world many countries are reducing their use of coal to generate electricity, replacing this with renewables like solar or wind power.

While steel production accounts for some 7.2% of global carbon, there are already pilot schemes to create steel using processes other than the carbon-intensive blast furnaces which are mostly used for industrial steel – though they are at very early stages.

Others are trickier: while there are some ideas knocking around to create carbon-free cement, they remain mostly conceptual.

There is no such thing as zero-carbon cement.

And given an enormous 18% of global emissions are down to agriculture and our use of the land, there remain big questions about how we can reduce those emissions while continuing to produce enough food for everyone and enabling farmers to carry on making a living.

These are thorny issues and while many economists assume that all the investment put into green technologies and solutions will eventually pay for itself, eliminating all these sources of emissions will be incredibly expensive and will involve lots of dead ends.

It is important to be open-eyed about this.

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Reducing emissions to net-zero isn’t a simple thing, in part because those emissions come from so many places and involve so many processes upon which we’ve become entirely reliant.

Net-zero cannot be achieved by planting a few trees or keeping lights switched off a bit more – much as that may help at the margins.

Just as important – if not more important – is to work out novel ways to procure the materials upon which modern life depends – everything from steel to aluminium to concrete.

If net zero is the goal, the route will involve essentially rewriting the rules of the industrial world.

Sky News broadcasts the first daily prime time news show dedicated to climate change.

Hosted by Anna Jones, The Daily Climate Show is following Sky News correspondents as they investigate how global warming is changing our landscape and how we all live our lives.

The show will also highlight solutions to the crisis and show how small changes can make a big difference.

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