Understanding the climate impact from air travel can be complicated. However, our new blog analyses the most up-to-date science surrounding aviation impact on climate change and highlights the key information affecting Aviation Impact Factors.

Offsetting the Climate Impacts from Air Travel

Interpreting the science behind the climate impacts from air travel is complex and difficult.  For the significant proportion of our clients for which emissions from aviation can account for up to 30% or more of their total carbon footprint, how we interpret the science is directly relevant to their carbon management strategies.

The CarbonNeutral Company periodically assesses the science behind this evolving issue, and reviews how the science is being interpreted by academics, policy-makers and regulators so that our treatment of emissions from aviation in The CarbonNeutral Protocol represents current best practice in carbon measurement and reporting. 

The issue of aviation’s impact on climate change first gained widespread attention in 1999, following a UN Intergovernmental Panel on Climate Change (IPCC) report which assessed the effects of aircraft on climate and atmospheric ozone.  That ground-breaking report introduced the term Radiative Forcing Index (RFI) to quantify the net atmospheric warming effects from aviation that go beyond direct emissions of greenhouse gases.  RFI is the ratio of total net radiative forcing from all high altitude impacts to the radiative forcing from only the greenhouse gas emissions from aircraft. The full report outlining this concept can be found here.

In the summer of 2014, we asked Prof John Murlis to provide us with guidance based on the latest science and the research presented in the 5th Assessment Report of the Intergovernmental Panel on Climate Change.  Prof Murlis’s paper is available here. It recognises strengthening scientific evidence that the impact of aviation on climate may be greater than from recognised greenhouse gases alone.  However, the scientific understanding of the exact cause and extent of the higher impact is still poor to fair.  Prof Murlis also cautions against using the term RFI to account for these complex impacts because that scientific term would imply a greater accuracy that is currently possible.  Instead, he proposed an ‘Aviation Impact Factor’ to represent the combination of long-term and short-term effects that cause net atmospheric warming above that from greenhouse gases alone. 

The CarbonNeutral Company, guided by the Murlis paper, has taken a view that for certifications under The CarbonNeutral Protocol, clients must consider the evidence regarding the overall effect of aviation on climate. Having done so, clients can then choose to calculate their aviation carbon footprints by considering only greenhouse gases (i.e. an Aviation Impact Factor of 1).  Alternatively, clients may elect to address the wider effects of aviation on climate by applying an Aviation Impact Factor of 2 to their emissions from aviation.

The CarbonNeutral Protocol does not mandate an Aviation Impact Factor higher than 1 for two main reasons:

Further, to the second point, few regulations exist to cover climate impacts from aviation, with the notable exception of the European Union’s Emission Trading Scheme for Aviation, which considers only emissions of carbon dioxide, and applies a RFI of 1.  DEFRA, the UK Government ministry responsible for environment, has provided guidance in support of a multiplier factor of 1.9.  This factor is not actively applied within any UK regulatory programme, or to any voluntary action on climate mitigation by the UK Government or its ministries.

The CarbonNeutral Protocol’s provision that clients may elect whether to apply an Aviation Impact Factor of 2 respects the voluntary nature of CarbonNeutral® certification.  However, it also signals that the strengthening case for a higher Aviation Impact Factor may require a different treatment of aviation in the future.  We continue to keep the issue under review.