Carbon offsets

Carbon offsets pay for projects that reduce the amount of CO2 in the atmosphere. Are they all equal?
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  • Updated:16 Sep 2008

05.How retailers were scored

Carbon Offset Watch’s scoring awarded points in the categories below. The ratings table shows the results.

Project type (7.5%)

The contribution to long-term sustainability of the type of projects used for offsets was assessed. Points were awarded to projects that change or prevent the underlying activities that create GHGs. Energy efficiency, renewable energy and the diversion of waste from landfill were awarded points. Projects that prevent deforestation would have got points too, but no Carbon Offset Watch participants sold that type of offset. Methane flaring, afforestation and reforestation projects were not awarded points.

Retailer’s service (19.5%)

This looked at whether retailers encouraged customers to reduce their emissions before buying offsets, provide sufficient information and accurately estimate the customer’s carbon footprint.

Accreditation or certification scheme (73%)

By far the biggest factor in determining retailers’ scores was the accreditation or certification scheme their offsets comply with. Carbon Offset Watch evaluated and ranked the schemes, taking into account:

  • How offset projects are validated and approved (19%).
  • Methodologies used to calculate emissions and offsets (7.5%).
  • Ensuring that the emission reduction wouldn’t have happened if you hadn’t bought the offset — that is, that the emission reduction or offset is truly additional (7.5%).
  • Independent verification that the carbon reductions happen (7.5%).
  • Independence of the accreditation scheme from the offset retailer (7.5%).
  • Publicly accessible registry of offsets (7.5%).
  • Verification and assurance that the offset can’t be double-sold; it should be ‘retired’ from the market when you buy it (9%).
  • Timing of emission reductions (7.5%). Immediate carbon reductions are best.
  • Permanence (maximum 7.5% penalty). This offset must be permanent and irreversible. Tree-planting schemes were penalised (there can be uncertainly about the permanence of carbon reductions from trees, which could be destroyed or die, releasing the stored carbon back into the atmosphere).

For a detailed explanation of how the schemes were ranked, go to Carbon Offset Watch

Dodgy calculations

As part of the research for Carbon Offset Watch, we checked the emissions calculated by retailers’ websites for one passenger’s return flights from Sydney to Melbourne, and Sydney to London. There’s no standard or consensus for the most accurate ways to estimate customer carbon emissions; the results were compared with two benchmark calculators to illustrate the range.

We found that retailers’ calculators differed from the benchmarks by up to 80%. That is, some retailers’ websites, which consumers are using to estimate their carbon footprint and the amount of offsets they purchase, are giving estimates that vary greatly from the benchmarks used. Most calculators underestimate, perhaps because they don’t factor the full lifecycle emissions (which take into account all emissions involved in the plane’s manufacture, not just its fuel use).


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