Zero carbon emissions means no emission of carbon dioxide (CO2) from any and all sources or human activities. It means there would be no burning of fossil fuels, which would have to be replaced by non-polluting renewable energy.  As a practical matter, zero carbon may be impossible at this moment in time, because for certain activities we have not yet found a non-polluting replacement.  Farming activities fall into this black hole.

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Net-zero carbon (or carbon neutral) is in some ways a recognition of this currently impossible goal as it allows for primary efforts to reduce and eliminate carbon emissions wherever possible.  To counter the carbon emissions that cannot yet be eliminated, we will have to rely on measures to balance or offset these carbon emissions.  An example is carbon capture and storage, where carbon emissions are removed from the air and stored or reused. Another example is converting huge areas of the earth to forests and wetlands as a means of carbon sequestration.

For every ton of carbon that we cannot eliminate, we will have to remove a ton or more of carbon already present in the air.  This is also called negative emissions.

The net effect is that we can eliminate the equivalent of all carbon emissions.  Then we will have net (or almost)-zero carbon emissions.

Some further ideas to explore on Net-Zero Carbon:

What are the challenges in adopting carbon capture and storage to remove carbon from the air?

What are the dangers of relying on planting forests to make up for uncontrollable carbon emissions?

What are the level of carbon emissions from agriculture (not methane) and what are the challenges in eliminating them?

Sources:

Rod Janssen, “Explaining what net-zero emissions means in practice,” Energy in Demand (8 June 2019).
bit.ly/2Y6issH

Edie, “Net-zero carbon.”  bit.ly/30ODrlK

Only Zero Carbon.  bit.ly/1SBk2IZ

“Carbon Neutral” in iePEDIA section of irish environment magazine (Jan 2017). bit.ly/2Y5fYuJ