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Aviation & Emissions Glossary

March 9, 2021
Harold Goodwin
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Carbon Neutral
Implies eans that while some emissions are still being generated these emissions are being offset somewhere else making the overall net emissions zero. Often used with no evidence either of carbon reduction or of the efficacy of the carbon offsets. No net release of carbon dioxide into the atmosphere, especially as a result of carbon offsetting. But see the problems associated with carbon offsetting.

Ecologi has published an explanation of the difference between Carbon Neutral and Net Zero. As they point out "carbon-neutrality can be achieved now, regardless of whether you have reduced your emissions or not."

Carbon Offsetting
Carbon Offsetting is an attractive option, a one-stop negotiable solution that allows the airline, tour operator or hotel to continue with business as usual.  But for the individual or business, it is a complex purchase. A 2017 study of offsets, commissioned by the European Commission, found that 85 per cent of carbon offset projects under the Kyoto Protocol’s Clean Development Mechanism (CDM) had failed to reduce emissions. This research clearly shows that many of even the very best offset schemes don’t work and that facilitating offsets without linking them to emission avoidance and reduction will never achieve the levels of overall emissions reductions that are needed.

  1. As you fly, CO2 immediately enters the atmosphere and contributes to greenhouse gas warming. Rates of sequestration vary, and precise calculation is not possible. It is generally reckoned that more than half of the CO2 emitted is removed from the atmosphere within a century and that some fraction (about 20%) of emitted CO2 remains in the atmosphere for many thousands of years. The pollution contributes immediately to global warming but it will take the offset years to sequester the carbon emitted.
  2. The carbon emitted by your flight does immediate harm but takes a long time to benefit the tree you planted – assuming the tree lives a full life and many do not. They rot on the forest floor emitting greenhouse gases.
  3. Where offsetting is delivered in ways that create no incentive to reduce emissions it is similar to a medieval pardon. Offsetting is cheap and if the consumer can be encouraged to make a voluntary contribution then there is no cost to the airline or operator. If offsetting becomes widely accepted it will reduce the pressure for reductions in carbon emissions and foster business as usual.
  4. Offsets are generally cheaper than changing technology to reduce emissions.
    10 myths about net zero targets and carbon offsetting, busted

Greenhouse Gases (GHGs)
Emissions of Carbon Dioxide, Methane, Nitrous Oxide and Fluorinated Gases.

Business dislikes regulation, so in the promotion of SAFs"mandates" are preferred.  Mandates are official orders or commissions to have a proportion of SAF in aviation fuel.

"the action of reducing the severity, seriousness, or painfulness of something"


Net-Zero is being widely used as a target. It combines two different ways of addressing climate change.

  1. Ceasing to emit greenhouse gas emissions
  2. Removing CO2 from the atmosphere using “negative emissions technologies” (NETs).

Net Zero is theoretically achieved when the two balance.  There are a number of dangers with this approach.

  1. It may become a polluter's charter where emission reductions are delayed in favour of NETs which may or may not deliver.
  2. "NETs are still only prospective technologies – they do not exist as large-scale socio-technical systems ready for deployment."
  3. The mitigation foregone by delay in emissions reductions may not be recoverable at a sufficient pace to avoid 2°C
  4. Global warming and climate change are a consequence of the growing concentration of GHGs in the atmosphere, if they accumulate in the atmosphere faster than they are removed by natural or anthropogenic processes Net-Zero is not achieved.
  5. Carbon put into forests, soils or even geological stores could leak back into the atmosphere, increased competition for land may, as it is in the Amazon, undermine this approach.

Climate scientists: concept of net-zero is a dangerous trap
More: The problem with net-zero emissions targets
Climate scientists: concept of net-zero is a dangerous trap
10 myths about net zero targets and carbon offsetting, busted
Ecologi has a detailed discussion of Net-Zero, including measures to "remove" carbon from the atmosphere including reforestation and afforestation (tree planting); blue carbon, soil carbon sequestration and biochar. Burning biomass is not carbon neutral. The release of greenhouse gases is immediate and adds to climate change - regrowing the trees only removes CO2 over many years.  In the short and medium turn, the volume of greenhouse gases has increased.
Net-zero is not the most ambitious sustainability strategy - zero carbon is.

We have known about the causal link between GHG emissions and climate change since 1856 ( Eunice Foote) and 1860 (Tyndall). Procrastination has been our main response,  for the last 160 years.

SAF Sustainable Aviation Fuel

There are basically three kinds of SAF, it suits the airlines wanting to pursue business as usual to lump them together.

  1. SAFw is made from waste, relies on large amounts of waste being available to make aviation fuel. It still puts greenhouse gases into the atmosphere.
  2. SAFb is biofuels - these inevitably compete with agriculture, pasture or fish production. This strategy prioritises aviation fuel over food and protein
  3. SAFe power-to-liquid fuels (PtL) use of synfuels derived from hydrogen and captured carbon emissions could become a scalable option. Such synfuels require water, renewable electricity to produce hydrogen, and CO2. Hydrogen can be used in fuel cells to produce electricity or combusted in engines.

The problem is that the pursuit of SAFw and SAFb delays the transition to decarbonised aviation -without large government research grants or taxation on aviation fuel there is insufficient incentive to transition to decarbonised aviation


Zero emission
Refers to an engine, motor, process, or other energy source, that emits no waste products that pollute the environment or disrupt the climate.



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