Contributes thermodynamics to climate change

Global air traffic contributes 3.5 percent to global warming

The share of global aviation in anthropogenic global warming is 3.5 percent. In addition, it can be seen that only a third of the climate impact of air traffic on CO2-Emissions are absent and two thirds are due to non-CO2Effects, with contrails and the resulting contrail cirrus being the most important factor. This is the result of an extensive international study conducted by the Manchester Metropolitan University with the participation of the German Aerospace Center (DLR), which was published on September 3, 2020 in the journal Atmospheric Environment.

The study is the first of its kind since 2009 and provides the most comprehensive insight yet into the effects of air traffic on the climate with calculations according to a new metric. The researchers evaluate all the factors that the aviation industry has contributed to climate change since its inception, including emissions of carbon dioxide (CO2), Nitrogen oxides (NOx) and the effect of contrails and contrail cirrus (clouds of ice crystals that are generated by aircraft engines at high altitudes under suitable meteorological conditions). Also included in the study are other climate-relevant emissions such as water vapor, soot, aerosol and sulfate aerosol particles that can be found in the exhaust plumes of aircraft engines.

Focus on Earth's radiation budget

With the first use of the further developed metric, which was introduced by the Intergovernmental Panel on Climate Change (IPCC) in 2013, the current study opens a new chapter in the analysis of the climate impact of air traffic. The new metric, known as effective radiative forcing (ERF), represents the increase or decrease in the balance between energy from the sun and energy emitted from the earth since pre-industrialization, and advancing with it the radiation budget of the earth's atmosphere is the focus of consideration. For the first time, the effects of spatially inhomogeneous effects are also taken into account in the calculations, such as the globally differently distributed occurrence and effects of contrail cirrus depending on air traffic and weather conditions.

"Using the new ERF metric, we found that the influence of the contrail cirrus has less than half of the previously estimated climate impact, but still makes the largest contribution of aviation to global warming," explains Prof. Robert Sausen from DLR -Institute for Atmospheric Physics in Oberpfaffenhofen. "On the one hand, contrail cirrus clouds reflect solar radiation into space; this has a cooling effect. On the other hand, they reduce the heat radiation from the earth; this warms the climate. Carbon dioxide emissions also make the second largest contribution to the climate impact of air traffic. In contrast to the effects of the contrail cirrus, which lasts for a few hours, the effect of CO lasts2 on the climate over many centuries, with this climate gas being largely evenly distributed over the long term.

32.6 billion tons of CO2

For the CO2-Emissions from global aviation over the entire history of the industry - considered between 1940 and 2018 - the study comes to the conclusion that 32.6 billion tons were emitted. About half of the total cumulative CO2Emissions were generated in the last 20 years alone, mainly due to the expansion of the number of flights, routes and fleet sizes, especially in Asia. The research team estimates that the figure of 32.6 billion tons accounts for around 1.5 percent of total human CO2Emissions. Will the non-CO2Including effects, the share of air traffic in all human activities that drive global warming is calculated at 3.5 percent.

The scientists undertook a comprehensive analysis of the individual factors of the climate impact of aviation in order to calculate for the first time an overall climate impact for global aviation. Similar less detailed studies were carried out in 1999, 2005 and 2009. In the future, it will be possible to compare the effects of aviation on climate change on the basis of these results with other sectors such as shipping, ground transport and energy generation.

Technologies to limit the climate impact

For the air traffic of the future, DLR is already researching methods and technologies to reduce CO2-Neutral aircraft to arrive with the help of biofuels, hydrogen and hybrid-electric drives. "The use of biofuels also leads to lower emissions of soot and thus to a smaller climate forcing due to the contrail cirrus" explains Dr. Ulrike Burkhardt from the DLR Institute for Atmospheric Physics in Oberpfaffenhofen. To reduce the non-CO2Effects, DLR is also investigating processes for optimizing flight routes and altitudes with the aim of minimizing climate impact. Alternative flight routes offer the possibility, for example, of avoiding regions and altitudes in which contrails would occur due to temperature and humidity.

The following are involved in the study under the direction of the Manchester Metropolitan University MMU (GB): National Oceanic and Atmospheric Administration NOAA (USA), University of Oxford (GB), DLR (D), Peking University (China), University of Colorado (USA) ), University of Leeds (GB), Center for International Climate Research CICERO (Norway), National Center for Atmospheric Research (USA), University of California, Irvine (USA), University of Michigan (USA), University of l'Aquilla ( I), University of Reading (GB).