The effect aviation has on the climate has been widely discussed – but what about the effect our changing climate has on aviation? RAeS Head of Research, NAOMI ALLEN FRAeS investigates.
When the words ‘climate change’ and ‘aviation’ are mentioned in the same sentence, it is typically to discuss aircraft emissions and their role in shifting meteorological trends. However, aviation is not immune from being affected by those changing weather patterns, and there is significant research taking place to understand how the sector will need to adapt.
The record-breaking temperatures seen in the UK this past summer are part of a clear trend and something that we are forecast to see more of.
Increasing temperatures impact on aviation in a number of ways, including having a direct impact on how an aircraft flies. The amount of lift generated by an aircraft decreases with increased temperature as a result of lower air density. Aircraft are designed to operate in a wide range of conditions and, therefore, warmer temperatures are unlikely to impact on the ability of an aircraft to operate in a general sense, but unexpectedly high temperatures in a specific locations can, undoubtedly, have an impact.
The first hurdle for some passengers will be being on board the aircraft when it takes off. Adverse weather conditions have long resulted in calls at the gate for volunteers to transfer onto alternate flights in order to lighten the load and reduce the take-off weight of the aircraft.
Every aircraft type’s performance data will include charts showing the required take-off distance for a given aircraft take-off weight, altitude and temperature. Since an airport’s altitude and maximum available runway length are fixed, in the case of elevated temperatures, the only available way to keep within the aircraft’s safe operating envelope is to reduce the take-off weight, potentially resulting in the off-loading of cargo or passengers. This is a problem which is inevitably more likely to occur at airports that are colloquially known as ‘hot and high,’ which combine higher altitudes and higher temperatures – although hot or high conditions could be enough to have an impact.
Airports, such as London City, with a short runway length, are also more likely to experience limitations on take-off weights, despite relatively benign altitude and average temperature conditions.
It is an issue that could potentially be addressed either through more powerful engines and/or airframes designed for improved take-off performance. However, neither of these are quick fixes and these improvements would need to be balanced against other performance requirements.
Therefore, it seems that seeing your aircraft departing without you due to a need to reduce take-off weight in increased temperatures may become more likely as global temperatures rise.
Climbing out
The impact of the reduction in lift caused by higher temperatures does not end when the aircraft leaves the ground. Research by the University of Reading suggests that aircraft climb angles away from airports could reduce by 1-3% on average, but on particularly hot days this may reduce by as much as 7.5%.
While this in itself may not be an issue, airports typically have stringent noise requirements to meet and a slower, shallower climb will increase the noise footprint of the aircraft. That means a predicted 4% increase in the number of people within the 50dB footprint of an airport by 2050.
Although a seemingly small increase, with the CAA’s Aviation Noise Attitudes Survey showing that typically 20% of people will consider that 50dB level ‘highly annoying’, it seems likely to have an impact on airport planning and restrictions in the future.
As the aircraft climbs, yet further changes in the atmosphere due to climate change may have an impact. Meteorologists have determined that freezing level heights (the altitude at which temperatures fall below 0°C) are increasing as a result of climate change.
Chinese researchers analyzing nationwide pilot reports have identified a significant upward shift of the primary icing layer which correlates strongly with the rising freezing-level heights.
It seems unclear how overall icing might change with changing global temperatures, with ground icing changes expected to vary depending on location. However, changes in the altitude at which icing could be expected may need to be considered in how these are managed during operations.
Turbulence ahead
Perhaps the impact of climate change in aviation which has been most in the public eye is the increase in Clear-Air Turbulence (CAT), which has resulted in several reported incidents on board aircraft.
Climate modelling has shown that wind shear is increasing at the altitudes typically used by civil aircraft in cruise. Meteorological observations have identified a correlation between increase shear instability and clear-air turbulence. CAT is a particular concern for aircraft as it occurs in cloud-free skies with little or no warning.
Although aircraft are built to withstand air turbulence, safety measures, such as wearing seatbelts, are generally only mandated when conditions suggest it is necessary – and in reality passengers often keep them undone unless the seatbelt light is lit. This makes unexpected severe turbulence a safety risk.
Storms and floods
In addition to these aircraft-specific impacts, the aviation sector is also subject to the same events caused by climate change as other industries. Researchers from Newcastle University have assessed the risk to major airports from flooding due to rising sea levels. The research highlights the importance of coastal airports to the global network, predicting that by 2100 between 10-20% of airports will be at risk of flood disruption. The cost of maintaining current risk levels for disruption due to flooding in 2100 is estimated as up to $57bn.
Storms are also predicted to become stronger as a result of climate change, with the potential for a higher frequency of storms in some areas. This is likely to cause both increased damage to infrastructure, as well as disruption to operations. EUROCONTROL reported in 2023 that between 2013 and 2019, on average, storms were responsible for up to 7.5% of total en route air traffic flow management delays. Their work suggests that the duration of delays could increase by around 20% by 2050, although the frequency of major storms and the resulting disruption would vary regionally with northern Europe expected to see an increase in storm activity, whereas a reduction in the frequency of storms is predicted further south.
One aspect of storms particularly pertinent to aviation is lightning. Research published in Science predicted an increase in the number of lightning strikes by 12% for every degree rise in global average air temperature. Based on a range of climate models, that could mean an increase in lightning strikes of 50% this century. Lightning strikes can have a range of potential impacts on aircraft – structural damage and interference with avionics or electrical systems are both possible, although occur rarely. Momentary pilot blindness due to the flash is also a possibility.
Although serious damage is rare, the potential for it necessitates a specific process be followed for any aircraft experiencing a lightning strike, requiring inspection and identification of any damage, followed by repair before the aircraft can return to service. Modern aircraft are more likely to be constructed from composite materials, which typically allow a lighter weight structure, thereby reducing the fuel burn required and resulting in a more efficient aircraft. However, composites inherently offer less protection from lightning strikes than metallic structures, requiring specific lightning protection be designed into the structure. Additionally, where damage does occur, composites are typically more complex and time-consuming to repair than a metal structure. Overall, a significant increase in lightning strikes is bad news for the airlines, likely resulting in an increased rate of aircraft out-of-service for either inspection or repair.
Predicting the wind
Climate change is also having an impact on wind patterns, which at the level of an individual flight may have either a beneficial or detrimental impact. Changes to the jet stream will affect transatlantic flights, with the expected effect being faster eastbound flights and slower westbound flights as a result of the strengthening jet stream. However, some studies suggest that the jet stream is becoming more erratic as a result of climate change. Predictability is an important element of flight operations, so any increase in uncertainty is likely to have an impact on both airlines and Air Navigation Service Providers (ANSPs) as they handle increased unpredictability. Airports may also need to adapt if arrival reliability is impacted.
Another aspect of changing wind patterns is their effect on airport operations. Airports have fixed runways aligned with prevailing winds, so changes to established wind directions can cause increased crosswinds and affect airport operations. Airports are also noting high winds and gusting winds having an impact on operations, with a need to better understand the associated risks and potentially put mitigation measures in place.
Airports are also having to consider allowing for more extreme temperatures when thinking about runway construction. In July 2022, flights were temporarily suspended at London Luton Airport due to runway damage caused by high temperatures. Materials better suited to very high temperatures can and are used at some airports around the globe, but the number of locations where this may be necessary is increasing.
Against a backdrop of concerns about the costs associated with the decarbonization of the sector, the inevitable costs of adapting to and mitigating the impacts of climate change is, undoubtedly, unwelcome. Nonetheless, a counterfactual perspective of the cost of not acting to reduce aircraft emissions on the aviation sector alone is a helpful additional perspective on the importance of efforts to decarbonize.
Summary
It is clear that climate change has the potential to impact aviation in a number of ways, some of them unique to the sector, while others will be similar to those faced by other industries. The adaptations required to mitigate the impacts described will affect stakeholders from across the sector, including airframers and engine manufacturers, airlines, airports, ANSPs and MRO organizations as a non-exhaustive list. Some of the mitigations will, inevitably, take significant time to implement, while others could be put in place more quickly. Climate scientists have recently presented evidence that warming has accelerated sharply since 2015, suggesting that aviation will need to continue – and perhaps accelerate – its efforts to adapt and mitigate the effects of climate change in order to continue safe and efficient operations.