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American Partners with Google on Contrail Avoidance

In a pioneering stride towards a greener aviation industry, American Airlines has unveiled the results of an unprecedented study on contrail avoidance. The study’s findings, validated by satellite imagery, underscore the airline’s commitment to mitigating the environmental impact of aviation. 

What are contrails?

Contrails, or those intriguing trails of cloud that airplanes leave behind, are formed when aircraft traverse layers of high humidity. These ephemeral sky signatures can linger as cirrus clouds for durations ranging from mere minutes to several hours, contingent on prevailing conditions. While this additional cloud cover can serve as a reflective shield, bouncing sunlight back into space during daylight hours, certain contrails have a nocturnal knack for trapping heat within the Earth’s atmosphere.

Contrail Avoidance Study Led by Google Research and Breakthrough Energy 

A comprehensive study was undertaken by Google Research and Breakthrough Energy, garnering support from American. The study’s primary objective was to ascertain the feasibility of identifying atmospheric zones likely to result in the formation of contrails. 

Furthermore, the team ventured to determine if pilots, equipped with data regarding these contrail-prone zones, could actively avoid creating contrails during flight.

“American is grateful for the opportunity to work with our partners at Google Research and Breakthrough Energy to help advance the science on contrail avoidance,” said Jill Blickstein, Vice President of Sustainability at American. “The results from this small-scale test are encouraging, and, while clearly there are more questions to answer about how to operationalize contrails avoidance across our industry, we’re excited to have played a role in establishing this first proof point. And we’re looking forward to sharing what we learned with stakeholders in the aviation industry and beyond.”

Can Google AI make flying more sustainable?

Google Research and Breakthrough Energy Harness Data to Map Contrail Forecasts

In a remarkable collaboration, Google Research and Breakthrough Energy have harnessed the power of vast data banks, including satellite imagery, weather, and flight path data, to create contrail forecast maps. This feat was accomplished using sophisticated artificial intelligence (AI). A select team of American Airlines’ finest pilots then took to the skies, conducting 70 flights over a period of six months. Guided by AI-generated forecasts, these skilled aviators tweaked the projected routes, thereby minimizing the creation of contrails. A truly ingenious fusion of technology and aviation expertise!

“Our contrails predictions combine the latest in AI research with massive amounts of satellite imagery, weather data and flight data,” said Juliet Rothenberg, head of product for Climate AI at Google Research. “We now have the first proof point that commercial flights can use these predictions to avoid contrails, as verified in satellite imagery. We’re grateful for our partnership with American Airlines and Breakthrough Energy – together, we’ve taken a significant step towards understanding a high-potential climate solution.”

Google Research delved into satellite imagery post-test flights capitalizing on AI capabilities. The findings were notable. When pilots used AI predictions to circumvent contrail creation, there was a 54% reduction in contrail formation, gauged by distance, in stark contrast to flights without such predictions. This initial evidence, though derived from a limited number of flights, demonstrates the potential of commercial flights to actively and verifiably steer clear of contrail creation. Further research is requisite to ascertain whether this success can be consistently reproduced and scaled up.

American Advancing Sustainability Through Contrail Avoidance

“Avoiding contrails might be one of the best ways to limit aviation’s climate impact, and now we have a clear demonstration that it’s possible to do so,” said Marc Shapiro, Director of Breakthrough Energy Contrails. “This study is a great example of what happens when creative, ambitious organizations work together to better understand and solve a tough problem, and we’re grateful for American’s and Google’s partnership.”

American Airlines strives to refine its operations as part of its sustainability commitment. The airline emphasizes fuel-efficient aircraft and innovative technologies powered increasingly by low-carbon fuel. Setting their sights on the goal of net-zero greenhouse gas emissions by 2050, American has laid down a series of ambitious stepping stones to reach this milestone. Earlier this month, American unveiled its 2022 Sustainability Report.

Learn more in Google Research’s video and blog post.

Google has partnered with the International Council on Clean Transportation (ICCT) to refine its Travel Impact Model (TIM). The ICCT supports efforts to improve the TIM’s carbon dioxide (CO2) estimates, incorporate non-CO2 climate pollutants like contrails, and credit sustainable aviation fuels and zero-emission planes. 

IATA Research on Contrails: Addressing the Climate Impact of Aviation Non-CO2 Emissions 

In recognition of the climate-warming effect of non-CO2 emissions from aviation, the International Air Transport Association (IATA) has taken a proactive stance. Through its active involvement in numerous initiatives, the association aims to monitor, develop strategies, and mitigate the environmental impacts of these emissions. 

Concurrently, IATA is committed to providing robust support for effective policymaking in this domain. This approach, they believe, will create significant strides toward a more sustainable future for aviation.

In a paper, IATA explains the origins and potential solutions for contrails

What are aviation’s Non-CO2 emissions?

Jet fuel emissions include CO2, H2O, NOx, SOx, CO, soot, UHC, aerosols, and -OH compounds, most of which are released 8– 13 km above sea level.  

Under specific conditions, water vapor from jets can condense into particles and atmospheric aerosols, forming clouds known as contrails.  

Non-CO2 aviation emissions impact climate change through persistent contrails, aviation-induced clouds, and atmospheric reactions triggered by NOx emissions. 

Measuring the climate impact of these emissions at a flight or airline level is complicated and comes with significant uncertainty.  

The amount of NOx an aircraft emits depends on engine design, technology, operating, and atmospheric conditions. These variables also influence contrail formation. 

Contrails’ climate effect is complex and depends on their persistence, formation conditions, combined effects, and whether they cool or warm the atmosphere.

Dynamic operational methodologies and cutting-edge technological implementations

Increasing fuel efficiency can decrease CO2 and non-CO2 emissions. But, some measures to reduce non-CO2 emissions might increase CO2 emissions. An example is reducing thrust to lower NOx emissions, which can prolong climbing times and increase fuel consumption and noise. Ensuring that non-CO2 reduction doesn’t lead to higher CO2 emissions is crucial. Technological options, such as lean-burn and Advanced RQL combustors and injecting atomized water droplets for engine cooling, can reduce NOx emissions by up to 40% and 50%, respectively. 

For contrail avoidance, flights can be diverted away from contrail-forming regions. However, this could increase CO2 emissions if the new flight path is longer. Success depends on accurate predictions of ice-supersaturated regions. A study estimated that diverting just 1.7% of flights could halve contrails’ total effective radiative forcing (ERF) with minimal fuel penalty and a slight increase in CO2 emissions. 

Improvements in navigation could provide climate benefits but require data not currently collected in real-time, such as relative humidity at cruise altitude. Accurate contrail forecasts would ensure flight diversions don’t lead to negative impacts, including additional CO2 emissions.

Neat SAF (Sustainable Aviation Fuels) May Provide Solution

Using neat (unblended) low-aromatic sustainable aviation fuel (SAF) is not currently allowed. However, studies have shown that neat SAF can decrease the number and size of soot particles, potentially reducing contrail cirrus clouds. 

Sulfur oxides (SOx) can increase contrail formation. Since SAF doesn’t contain sulfur, it eliminates SOx ‘s impact on contrail creation.  

By 2030, manufacturers aim to produce 100% SAF-compatible aircraft.  

Electric propulsion would eliminate all CO2 and non-CO2 emissions, but current battery technology limits their use to sub-regional aircraft. These aircraft fly at altitudes where contrails don’t form.  

Hydrogen aircraft would stop all carbon emissions, including soot particles that form contrails. Yet, they would emit more water vapor than conventional jet fuel or SAF and would still create contrails, albeit different types.  

Hydrogen contrails would likely consist of larger but fewer ice crystals. Further research is needed to understand their optic density, duration, and radiative forcing. Hydrogen would eliminate NOx emissions entirely in a fuel cell-powered electric aircraft or significantly reduce them if used in a jet engine.


More on Google’s work to support airline sustainability targets

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