Operating in a carbon constrained world

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A fundamental change in air travel behaviour and technology will become a necessity if climate protection measures such as a halving global emissions by 2050, are to be achieved.

"Given the size of this sector, already superseding that of large nations, the inclusion of international aviation in the second post-2012 commitment period under the Kyoto Protocol could allow this sector to play its role within the overall mitigation effort across all sectors," says Dr Sarah Raper of Manchester Metropolitan University.

The study, part of the UK's Omega aviation research initiative, is intended to help UK decision makers by putting the effect of aviation on climate in perspective and help determine whether there is a need for a substantial deviation from business-as-usual aviation growth scenarios in a future that seeks to mitigate the effects of global warming.

Using a simple Magicc gas cycle-climate model, adapted to account for non-carbon dioxide aviation emissions such as high-altitude NOx emissions, contrails and aviation-induced cirrus, the researchers examined the radiative forcing - or the global warming effect - in the UK due to greenhouse gases controlled under the Kyoto Protocol and therefore non-aviation sources.

The researchers found that up to the mid-to-late 1960s these contributed more to climate change than aviation, at which point air travel started to overtake.

"A strong increase of total anthropogenic forcing after 1970 affects the relative role of aviation and UK Kyoto-greenhouse gas emissions to the extent that the UK forcing share declines after 1970 while the aviation share still increases, but less strongly than before 1970," says Raper.

The aviation contribution to global-mean temperature change exceeds that of the UK Kyoto-greenhouse gases from around the 1980s.

"Our analysis suggests that the UK climate contribution since 1940 was likely to have been lower than the aviation contribution throughout the 20th century. In 2005, we estimate that temperatures are 0.028°C [0.05°F] higher due to aviation, with further increases expected for the future," says Raper.

The team then generated a range of aviation growth scenarios from 2000 underpinned by a global multi-sector mitigation approach that would see a halving of greenhouse gas emissions by 2050 relative to 1990, with further reductions, a long-term vision referred to by the G8 countries and within the Kyoto Protocol negotiations as a minimum requirement to avoid dangerous levels of climate change.

"Our set of aviation reference scenarios suggests that as early as 2045, the aviation share of global fossil carbon dioxide emissions could exceed 20% in a carbon constrained world. "This result indicates a fundamental inconsistency between standard aviation growth forecasts and lower global mitigation pathways," says the report.