Aviation’s Climate Change Debate gets more confusing

Climate Change science Debate
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Distrust of Science an increasing American Phenomena 

Manchester Metropolitan University definitive study of Aviation CO² impact

Articles 1/2 cite POSITIVES 1/2 NEGATIVE

American’s distrust of science is at an all-time high. Aviation is an industry which depends in science and engineering for its existence and future development. It could be argued that some of dichotomy can be attributed to honest debate on controversial issues.

The impact of flight on the environment is a subject for which there may be differences of expert opinions. The Green Party, based on its sources, assert that airlines are a major reason for CO2 propagation. The industry steadfastly disagrees with the degree of its contribution, but has agreed to goals that will further reduce its emissions.

This conundrum is exemplified by the below series of articles. Initially, it was reported (#1) that the CO2 impact was less than previously reported. This claim was based on an extensive scientific analysis. The next article, written by  Manchester Metropolitan University, the employer of the lead researcher, has a headline with the same positive mention. Article #3 repeats that the past CO2 estimates were overstated.

All three include the MMU Report’s determination that the aviation’s operations have doubled their total CO2 emissions.

The fourth, fifth and sixth articles, based on the exact same report, headline the other finding of this scientific analysis—aviation in the last 20 years has doubled its impact on the environment. The writers included the reduction of the CO2 in a later paragraph.

One scientific analysis, based on all the relevant data and analyzed by the most sophisticated analytical tools, results in opposite conclusions in the headlines. No wonder many distrust science, but more tellingly, on what finding(s)will the policy decision rely?

  1. Positive


Aviation A Smaller Contributor To Climate Change Than Previously Thought


Aviation has a smaller impact on climate change than previously thought but it’s also growing rapidly and its effects are more complex than other contributors according to a new study. A team of European climate scientists has recrunched the numbers and determined that aviation is responsible for 3.5 percent of the global warming effect that results from human activities. Previous estimates pegged the aviation contribution at about 5 percent. The new data takes into account some balancing factors in the ways that aircraft pollute.

For instance, nitrogen oxides emitted in aircraft exhaust increase the production of ozone, a major greenhouse gas, but they also destroy methane, a big contributor to atmospheric warming. Also, contrails heat and cool the planet at the same time by trapping atmospheric heat while reflecting sunlight. The net result is that contrails are only about half as bad as previously thought. The scientists say that despite the findings, aviation still needs to clean up its act and the COVID-created hiatus in aviation activity isn’t going to help much. “It’s not going to make much difference in the long term,” said researcher David Lee at Manchester Metropolitan University in the U.K.

Manchester Metropolitan University; David Lee







Aviation contributes 3.5% to the drivers of climate change that stem from humans

CO2 MMU masthead

CO2 contrails graph

Study, led by Professor David Lee, is the most comprehensive analysis of its kind

Aviation has been calculated to be 3.5 per cent of all human activities that drive climate change, new research shows.

Manchester Metropolitan University led the new international study that provides unprecedented calculations of the impact of aviation on the climate from 2000 to 2018 to produce the most comprehensive insight to date.

Lead author David Lee, Professor of Atmospheric Science at Manchester Metropolitan University and Director of its Centre for Aviation, Transport, and the Environment research group, said the findings show that two-thirds of the impact from aviation is attributed to non-carbon dioxide emissions and the rest from CO2.

The research was carried out in collaboration with numerous academic and research institutions across the globe over the past five years.

The analysis – published in the journal Atmospheric Environment – is the first of its kind since 2009 and will be of significant use to stakeholders such as policymakers, industry bodies and non-government organisations.

Researchers evaluated all of the aviation industry’s contributing factors to climate change including carbon dioxide (CO2) and nitrogen oxide (NOx) emissions, and the effect of contrails and contrail cirrus – clouds of ice crystals created by aircraft jet engines at high altitude.

This was analysed alongside the water vapour, soot, and aerosol and sulfate aerosol gases – fine particles suspended in the air – found in the exhaust plumes emitted by aircraft engines.

First set of calculations

The study is unique because it is the complete first set of calculations for aviation that uses a new metric introduced in 2013 by the Intergovernmental Panel on Climate Change.

This metric is called ‘effective radiative forcing’ (ERF) and represents the increase or decrease since pre-industrialisation times in the balance between the energy coming from the sun and the energy emitted from the earth, known as the earth-atmosphere radiation budget.

Using the new ERF metric, the team found that contrail cirrus’ impact is less than half than that estimated previously but still the sector’s largest contribution to global warming, by reflecting and trapping escaping heat from the atmosphere.

Carbon dioxide emissions represent the second largest contribution but unlike the effects of contrail cirrus, CO2’s effect on climate lasts for many centuries.

Understanding impact is vital

Prof Lee said: “Given the dependence of aviation on burning fossil fuel, its significant CO2 and non-CO2 effects, and the projected fleet growth, it is vital to understand the scale of aviation’s impact on present day climate change, especially in view of the requirements of the Paris Agreement to reach ‘net zero’ CO2 emissions by around 2050.

“But estimating aviation’s non-CO2 effects on atmospheric chemistry and clouds is a complex challenge for contemporary atmospheric modeling systems.

“It is difficult to calculate the contributions caused by a range of atmospheric physical processes, including how air moves, chemical transformations, microphysics, radiation, and transport.”

The scientists undertook a comprehensive analysis of individual aviation ERFs to provide an overall ERF for global aviation for the first time.

Similar studies were conducted in 1999, 2005 and 2009 but this is the most current and most extensive, with lots of the details in the science having changed and matured.

Professor Lee added: “The new study means that aviation’s impact on climate change can be compared with other sectors such as maritime shipping, ground transportation and energy generation as it has a consistent set of ERF measurements.”

Effects of global aviation

Prof Lee and his team calculated that the cumulative CO2 emissions of global aviation throughout the course of the industry’s entire history – defined as between 1940 and 2018 – were 32.6 billion tonnes.

Approximately half the total cumulative emissions of CO2 were generated in the last 20 years alone, attributed largely to the expansion of the number of flights, number of routes and fleet sizes, particularly in Asia, though partially offset by improvements in aircraft and jet engine technology, larger average aircraft sizes and increasing efficiency in the use of aircraft capacity to fit more passengers in the same space.

The research team estimated the figure of 32.6 billion tonnes accounted for 1.5 per cent of total CO2 emissions ever at that point.

And when the non-CO2 impacts were factored in, aviation’s was calculated to be 3.5 per cent of all human activities that drive climate change.

The researchers noted that while the 2016 Paris Agreement on climate change does include domestic aviation in individual country’s reduction targets, it does not address international aviation, which accounts for 64 per cent of air traffic.

Unlike direct emissions of non-CO2 greenhouse gases, such as nitrous oxide and methane from sources such as the agricultural sector, aviation’s non-CO2 effects are not covered by the former Kyoto Protocol.

Professor Lee added: “It is unclear whether future developments of the Paris Agreement or International Civil Aviation Organization negotiations to mitigate climate change, in general, will include short-lived indirect greenhouse gases like nitrogen oxides, contrail cirrus, aerosol-cloud effects, or other aviation non-CO2 effects.

“Aviation is not mentioned explicitly in the text of the Paris Agreement, which says total global greenhouse gas emissions need to be reduced rapidly to achieve a balance between man-made emissions and sinks of greenhouse gases in the second half of this century.

“As the COVID-19 pandemic changes, aviation traffic is likely to recover to meet projected rates on varying timescales, with continued growth, further increasing CO2 emissions and, of course, historical emissions of CO2 take many centuries to be removed.

“Therefore, reducing CO2 aviation emissions will remain a continued focus in reducing future man-made climate change, along with aviation’s non-CO2 contribution.”

The study suggests solutions that include re-routing flights to avoid creating contrail cirrus but the trade-off is a longer flight path and more fuel burnt, producing more greenhouse gas emissions.

The team also noted how changes to combustion technology to reduce NOx emissions can increase CO2 emissions.

Strengthening the scientific foundation

Co-author David Fahey, Director of the Earth System Research Laboratories at the United States’ National Oceanic and Atmospheric Administration, and a Visiting Professor at Manchester Metropolitan University, said: This study is a great example of an international collaboration to clarify how human activities cause climate change.

“Our assessment has strengthened the scientific foundation of the role of aviation in the climate system and established a framework for future assessments.

“Our assessment will aid decision makers and the industry in pursuing any future mitigation actions while protecting this important sector from any inaccurate assertions concerning its role in the climate system.”


  1. Positive

Major new study finds global aviation is responsible for 3.5 per cent of human-induced climate change


co2 contrails








Aviation’s contribution to global warming has doubled since 2000

co2 4 engine jet with contrails

The most comprehensive analysis so far of how much warming is caused by aeroplanes has found that flying’s contribution to global warming nearly doubled between 2000 and 2018. Rapid growth is far outpacing efforts to reduce its contribution.

“It is growing so rapidly,” says David Lee at Manchester Metropolitan University in the UK. “It’s just astonishing.”

The study only goes up to 2018, before the big decrease in flying due to the coronavirus pandemic, but this is just a blip, says Lee. “It’s not going to make much difference in the long term.”

Flying has extremely complex effects on the climate. For instance, the soot from jet engines triggers the formation of contrails that, like clouds, can have both a warming effect by reflecting outgoing heat back down to Earth’s surface and a cooling effect by reflecting sunlight back into space.

Similarly, nitrogen oxides from the engines can increase the formation of ozone, an important greenhouse gas, but also destroy methane, another potent greenhouse gas.

So, the team behind the new analysis, which included Ulrike Burkhardt at the Institute of Atmospheric Physics in Germany, used computer models to improve on previous estimates of the overall effect. These suggest that contrails cause less than half as much warming as previously thought.

Even so, short-lived contrails still lead to more warming than the long-lasting carbon dioxide emissions from aircraft.

Overall, the team calculated that flying is responsible for 3.5 per cent of the global warming effect resulting from human activities. That is less than previous estimates of around 5 per cent. Figures suggesting that flying is responsible for around 2 per cent of carbon dioxide emissions don’t take into account the other ways in which flying causes warming.

This contribution of 3.5 per cent has remained relatively constant since 2000, but only because other sources of warming have also increased rapidly. Over this period, the warming effect from flying has nearly doubled.

“It’s the growth that is the real feature,” says Lee. “It is rising quite dramatically.”

Switching to biofuels – such as palm oil – isn’t the answer, he says, because when the full effects of growing crops for biofuels are taken into account, it isn’t clear that they reduce emissions much, if at all.

However, using renewable energy to turn carbon dioxide from the atmosphere into synthetic kerosene could greatly reduce emissions. Switching to synthetic kerosene would make individual flights carbon neutral. It would also halve the warming effect from contrails, says Lee, because synthetic kerosene doesn’t contain the aromatic chemicals that produce most soot.

“It’s feasible, but we don’t know how to do it at scale,” he says. “And as long as it’s cheaper to dig it out of the ground, it’s never going to happen.”

A major policy initiative is required, he says, such as setting a date beyond which the use of fossil kerosene will be banned.

5-6 Negative

Global Warming: Aviation produced 26BN tons CO2 in 20 years

Aviation’s contribution to global warming doubled in past 20 years

scientific debate


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