Previously, a few studies concluded that making minor adjustments to the flight paths of only a small fraction of aircraft could significantly reduce the impact of global warming. Now, a new paper has found that these changes could be quite cost-effective.

The climate concern that airlines generally worry about is that aircraft emit a large amount of carbon dioxide when burning fuel. However, aircraft also release heat, water vapor, and particulate matter, which can form thin clouds called "contrail" in particularly cold, humid, and icy parts of the atmosphere.

When a large number of flights pass through these areas, these contrails can form cirrus clouds, absorbing radiation that escapes from the surface, as if they were a blanket floating above the Earth.

It is estimated that this phenomenon of cirrus cloud formation may account for about 35% of the total impact of the aviation industry on climate change, or about 1% to 2% of the total degree of global warming.

Among all flight routes, about 80% of contrails are produced by 2%-10% of the routes. Therefore, many people believe that simply changing the routes of these flights can significantly reduce this impact, providing a potential method that is effective, cost-effective, and fast for mitigating climate warming.As reported by The New York Times, Breakthrough Energy, Google Research, and American Airlines announced some promising results in the summer of 2023, stemming from a research collaboration between the three entities.

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They utilized satellite imagery, weather data, software models, and artificial intelligence predictive tools to guide pilots to fly above or below areas where the aircraft might produce contrails.

American Airlines employed these tools in 70 flights over a period of six months, and subsequent satellite data indicated that their total contrail length was reduced by 54% compared to flights that did not alter their routes.

Of course, implementing such strategies would increase costs. Aircraft typically require more fuel to avoid these areas, which also implies that flights would emit more greenhouse gases.

For airlines, more fuel also means greater expenditure, and if it is difficult to afford, they are unlikely to voluntarily implement these measures.A new paper published in Environmental Research: Infrastructure and Sustainability explores this issue, where researchers combined a commercial tool for optimizing flight paths with a flight simulation tool.

The latter contains data from nearly 85,000 domestic and international flights of American Airlines under various weather conditions in summer and winter.

In these simulations, researchers found that reducing the warming effect of contrails by 73% only increased fuel costs by 0.11%, and overall costs by 0.08%, which is the average of tens of thousands of flights.

In the simulations, only about 14% of flights needed to be adjusted to avoid forming contrails that lead to further warming.

"There is clearly a trade-off between increasing fuel and reducing harmful contrails. This contradiction is real and is one of the biggest challenges facing this climate solution."The co-author of the paper and the Director of the Contrails Team at Breakthrough Energy, Marc Shapiro, said, "But we showed in the paper that the increased fuel consumption is much less than we expected."

It is understood that the organization, founded by Bill Gates, aims to stimulate clean energy innovation and address climate change.

He said that airlines can also use this commercial trajectory tool to make decisions that balance cost and climate goals.

For example, when the cost of adjusting the flight path is particularly high, they can continue to use the flight path that will form contrails.

Other research teams and airlines are also evaluating this concept through some projects, including the cooperation between Delta Airlines and the Department of Aeronautics and Astronautics at MIT.There are other methods to reduce the formation of contrails, including switching to different types of fuel or continuing to develop more powerful electric or hydrogen-powered aircraft.

However, research to date has shown that changing flight paths may be one of the simplest ways to significantly reduce the warming effects associated with contrails.

Steven Barrett, head of the Department of Aeronautics and Astronautics at MIT, said: "So far, this will be the cheapest and fastest way to reduce the climate impact of the aviation industry. It looks promising."

He added that finding any method to make short-term progress in aviation is particularly important, as developing and implementing scalable, affordable solutions to address emissions caused by the use of heavy oil (fuel oil) may still take a long time.

However, more modeling studies and real-world experiments are needed to prove whether the "contrail avoidance" methods we currently know are as effective as people hope.Barrett said that, first of all, researchers still need to test, refine, and design systems that can reliably predict when and where contrails will form on aircraft, and have enough time to change flight paths, all of which are carried out under constantly changing weather conditions.

There are still some thorny complex issues that need to be resolved, such as cirrus clouds that can also reduce warming by reflecting the shortwave radiation from the sun.

The loss of this cooling effect must be taken into account in the calculation of any net (climate) benefits. Or, perhaps there are ways to avoid this loss.

For example, Shapiro said, one strategy might be to only change flight paths in the evening and at night, which would eliminate the complexity of sunlight reflection.

In addition, any warming reduced by eliminating contrails must be far greater than the warming brought about by the increase in greenhouse gas emissions.When we weigh whether to be more concerned about short-term or long-term warming, this becomes a more thorny issue: not producing contrails would bring immediate benefits.

However, any increase in carbon dioxide may take decades to exert its full warming effect, and they may persist for hundreds to thousands of years.

At least, this new study found that even considering the additional greenhouse gases, reducing contrails would reduce the net warming impact within 20 and 100 years, but the effect would be weaker in the case of 100 years. But this also needs further evaluation through additional research.

Another unresolved issue is whether airspace restrictions and traffic bottlenecks will limit the ability of airlines to regularly change the necessary routes.

The next step, Breakthrough Energy, hopes to collaborate with airlines to explore some of these issues by expanding real-world flights and observations.However, even if subsequent research continues to indicate that this is a fast, affordable method to mitigate global warming, we do not know whether airlines would be willing to do so if regulatory bodies do not compel them.

Although the fuel cost to achieve this goal may be small in percentage terms, the total cost could increase rapidly across the entire fleet over time.

Nevertheless, the authors of the study assert that they have shown that flight paths that avoid the formation of contrails can "bring significant short-term climate benefits at a lower cost than most other climate interventions." In their view, this approach "should become one of the main concerns of the aviation industry in the coming years."