Worldwide aviation is one of the most rapidly growing sources of CO2 emissions, claims new research study
Wed 8 Apr 2009 – The total influence of aviation on climate is considerably greater than has been suggested solely on the basis of its current 2.8% share of current anthropogenic fossil CO2 emissions, says two leading European climate researchers. Their analysis shows that from its beginnings in 1940 through to 2005, civil aviation has been responsible for a rise in global mean temperatures of around 0.028 degrees C, representing approximately 4.7% of the total anthropogenic change.
These are the main conclusions of an Omega-funded study to assess the potential impact of aviation growth on global temperature changes carried out by Dr Sarah Raper, Senior Research Fellow at Manchester Metropolitan University’s Centre for Air Transport and the Environment (CATE), and Dr Malte Meinshausen of the Potsdam Institute for Climate Impact Research. They say a fundamental change in long-range transportation behaviour and technology is a necessity if climate protection scenarios, such as halving global emissions by 2050, are to be realised.
Worldwide aviation is one of the most rapidly growing sources of CO2 emissions, showing an increase of 42% between 1990 and 2005, report the authors. Their analysis shows that from its beginnings in 1940 through to 2005, civil aviation has been responsible for a rise in global mean temperatures of 0.028°C (68% range 0.023-0.050), representing approximately 4.7% of the total anthropogenic change. Aviation emissions rose to an estimated value of 663 MtCO2 per year by 2000.
Its present contribution to climate change is comparable to that of a major economy such as the United Kingdom but, unlike the UK, the share is increasing and might increase even more steeply in the future, say the authors.
“When assessed in the context of a climate change mitigation scenario, most aviation projections give cause for concern,” says Dr Raper, lead investigator on the study.
Using the greenhouse gas-cycle climate model MAGICC, the researchers have assessed the complex radiative forcing effects of non-CO2 aviation emissions such as NOx and jet engine induced contrails, which form the two most important contributors to aviation forcing apart from CO2. The model was adapted to account for high-altitude NOx emissions and their higher efficiency compared to ground-based emissions in terms of both increasing tropospheric ozone and reducing methane lifetime. Ozone and methane are two of the Kyoto-defined greenhouse gases. Current knowledge on contrails and aviation-induced cirrus cloud forcing has been included in the analysis.
A range of aviation scenarios from the year 2000 onwards has been generated using the IEA/SMP Transport Model, which the researchers suggest that as early as 2045, the aviation share of global fossil CO2 emissions could exceed 20% in a carbon-constrained world. “This result indicates an incompatibility between standard aviation growth forecasts and lower global mitigation pathways,” say the authors.
The analysis found that in 2005 about 25% of forcing was due to the long-lived greenhouse gases like CO2, whose accumulation with time in the atmosphere tends to lead to a continuous increase in aviation forcing even when emissions remain constant. This means the majority of the forcing in a given year is due to emissions within that year. Therefore, the relative importance of short-lived effects, for example cirrus-induced clouds from contrails, offers opportunities for mitigation strategies that attempt to reduce forcing in the short term.
The researchers intend their study to help policy makers as they decide on what course of action they should take on including international aviation in the post-2012 commitment period of the Kyoto Protocol. “Our analysis is a contribution towards answering whether there is a need for a substantial deviation from business-as-usual aviation scenarios in a future that seeks to mitigate the effects of global warming,” they conclude.
