What actually is Net Zero?

Net-zero is a term that has gained significant attention in recent years.

The Paris Agreement, adopted in 2015, aims to pursue a 1.5 degrees Celsius increase of global temperatures. To achieve this goal, the agreement calls for a reduction of global greenhouse gas emissions such as CO2 (carbon dioxide) as soon as possible, and to achieve a balance between sources and sinks of greenhouse gases. This is often referred to as achieving "Net Zero emissions".

How is Net Zero defined officially?

The Intergovernmental Panel on Climate Change (IPCC) defines Net Zero as "a state where anthropogenic (man-made) CO2 emissions are balanced by anthropogenic removals of CO2 over a specified period, resulting in no additional warming effect". This can be achieved through a combination of reducing emissions and greenhouse gas removal (GGR) techniques, both through biological approaches such as such as reforestation and negative emissions technologies (NETs) such as carbon capture and storage.

What does this mean, in simple terms?

Well, imagine a bath tub…

It might not be the best idea to overfill this one.

Think about the amount of CO2 in the earth's atmosphere as the water in the bath.

We have realised the tap (our emissions) is running too much: we are going to overfill the bath. Too much CO2 means the earth warms, which will lead (and already is leading) to catastrophic climate impacts this century. This also includes other greenhouse gas emissions such as methane, but for simplicity we'll stick to the main offender: CO2.

In a sentence, it means achieving a balance between emitting and absorbing greenhouse gases, resulting in zero net emissions.

So, we need to turn off the tap, right?

Yes: we do need to reduce our emissions. This means rapidly transitioning to renewable energy, and being extremely careful about whether we invest in new oil and gas exploration projects, Energy is crucial: the energy sector is the source of around three-quarters of greenhouse gas emissions today and holds the key to averting the worst effects of climate change. But that's not going to be enough.

The fact is, it's not going to be possible to stop all emissions, everywhere, any time soon. We don't have good alternatives yet for a lot of materials like steel, many chemicals, or sectors like aviation and shipping that are needed for our critical infrastructure. These are known as 'residual' emissions.

So, the tap is going to stay on. The bathtub will keep overfilling. Because of the way carbon persists in the atmosphere, we can expect to see locked-in levels of warming for thousands of years. Therefore as we work towards decarbonising the economy to achieve a balanced level (Net Zero) we also need to let water out the bath somehow.

So, how do you open the drain?

This means investing in approaches and technologies that actively remove carbon from the atmosphere.

Luckily, there is a naturally occurring organism that removes CO2 from the atmosphere: plants! According to NASA, plants in areas like forests sequester (absorb) +15 billion tonnes of CO2 every year (!!). So, we need to invest in land restoration, the planting of trees, and protection/promotion of coastal and ocean habitats (such as mangroves and kelp forests), as a key route to compensate for emissions that occur elsewhere. Nature-based solutions, when appropriately governed and when empowering and respecting traditional land owners, can be an important tool in sequestering CO2.

However, they do present an issue of permanence (trees die, or can be lost due to forest fires!) as well as raise issues in accounting for how much CO2 is absorbed, and additionality.

We can also invest in technologies that actively remove carbon from the year: these are known as Negative Emissions Technologies (NETs). However, CCS technologies are unproven at scale, and are currently not cost-effective in removing carbon: they are currently too expensive. In addition, NETs may also legitimise more fossil fuel extraction, as they essentially let us off from emitting, when it is urgent that we transition our economy away from reliance on this energy source.

While it's important we explore and invest in NETs, it's even more important we shift away from our major sources of emissions, and protect and promote our natural habitats that sequester CO2.

In summary: we need to take major steps to reduce our active greenhouse gas emissions. However, seeing as that will not be fully possible for all industries, we'll need to remove CO2 from the atmosphere, mainly by natural absorption via plants, but also by investing in new technologies. While Net Zero hints at balance, the crucial aim is to get to Net Negative Emissions: removing more CO2 than we put in.

That way, the bathtub level will fall instead of rise, meaning less of a mess for future generations.

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