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Could aviation emissions be reduced by building 'half-way-there-ports' in the sky?



Seamless take-off and landing of aircraft could be achieved through the design and building of the Portocielo at key locations in the airport network. By placing runways in the sky, the distance planes are required to climb is reduced, the introduction of novel take-off methods becomes a possibility, and aircraft can take advantage of smoother and faster air. Such benefits could greatly reduce fuel use and therefore emissions in the aviation sector. More importantly, by reducing the power required for take-off, it could open the door to fuel sources of the future such as solar power.


The Portocielo structure consists of a series of interconnected runways situated around a central maintenance hub. The runways are supported by several skyscraper 'pillars', serving as separate terminals for check-in, and which also provide passenger lifts between the ground and the runways, hotel accommodation and sleeping pods for travellers, as well as additional airport facilities, restaurants and entertainment. The Portocielo is well-connected to the closest cities by rail and/or bus, and the land beneath the runways offers a terminus for these connections. Additional uses for this space are discussed in other sections.


The most emission intensive stage of air travel is during take-off. The Portocielo offers two key opportunities to reduce emissions in this regard. By building the airport in the sky at maybe a few hundred metres, distances to climb are less. Diagram A illustrates that the height of the airport can be optimised to achieve the reduction in climb height whilst considering the capital emission costs of building higher. As illustrated in diagram B, there is a novel opportunity to use gravity to achieve the acceleration needed for lift. The plane can be accelerated to an optimised speed which allows it to clear the end of the runway. Then following a negative trajectory angle to accelerate further. The plane can climb as usual once lift speed is reached.

What actions do you propose?

First of all, research must be undertaken into the emission-reducing potential of present day aircraft using the Portocielo. Research should also attempt to incorporate developments in the research of new aircraft designs that may be used in the future. Research should include studying the effects of emissions from current aircraft into different parts of the atmosphere since the emissions can behave differently depending on their location in the atmosphere.

Once a blueprint has been created for an airport that can assist in the reduction of emissions and facilitate advances in aircraft technology, we would look to identify a pair of airports. Factors used to determine which airports to replace initially would include the size/activity and passenger numbers, and how the demand for the airport is expected to grow, but also the age of the airport and any plans to replace runways etc. We would then encouarge the following processes:

  1. Make proposals to potential investors or governments

  2. Establish a partnership between the two locations planned for the building of the Portocielo

  3. Establish the needs of the community and environment within which the Portocielo is to be built, assess business opportunities associated with it and connect to and enhance existing ground transport infrastructure

As well as being used for rail and bus links, it is intended that the ground underneath the Portocielo runways be used to provide pleasant spaces – for travellers and locals alike- with features and facilities varying depending on location. These might include parks, botanical gardens, play areas, woodland with walking trails, exercise equipment and perhaps even indoor centres offering classes or workshops. The idea is to offer travellers with connecting flights and long stopovers the chance to spend some time in the surroundings of the local area, when, for example, exploring the nearest city isn't an option due to time constraints. Additionally, the space is intended to impact positively on the local community, offering opportunities for exploration, relaxation and new activities.

Following support from communities, governments and developers the Portocielo pair would be built. In the following years the design would be improved and further Portocielos built to form the network.

Who will take these actions?

Scientists, engineers, architects, businesses and government are all needed to bring the Portocielo project to fruition either through their roles in research or implementation. It is the role of national and local governments and businesses to take up positive action on sustainable development of air travel in their region.

Development of airports is generally taken on by government but private investors may involved. Each will have strong but usually differing motivations. Private investors have the opportunity to patent and profit from a game-changing approach to air travel, while government agencies stand to benefit through the mitigation of climate change while providing for the aspirations of the population they represent.

Where will these actions be taken?

As the aim is to create a reduction in global emissions from the aviation industry, actions will be taken to connect the world's key hubs via the Portocielo, ideally beginning with the replacement of some of the largest airports.  Currently the busiest airports in the world are situated in Atlanta, Beijing, Dubai, Tokyo and London. Fast-growing airports such as Seoul, Delhi and Mumbai may also offer possible options. Additionally, key hubs in other continents such as South America and Africa should be explored to create a worldwide network.

How much will emissions be reduced or sequestered vs. business as usual levels?

According to the IPCC AR5 report, international aviation emissions increased 63% from 1970 to 1990 and 80% from 1990 to 2010. Emissions from international aviation in 2010 were 0.46 GtCO2e/yr. Given the likely huge increase in demand we think it might be reasonable to extrapolate this trend. If so, projected emissions for 2030 would be 0.91 GtCO2e/yr and for 2050 would be 1.95 GtCO2e/yr.

IPCC emission pathways to restrict warming to 2 degrees suggest that global emissions should be around 20 GtCO2e/yr in 2050. Aviation would account for 10% when it only made up 1.5% of 2010 emissions.

We suggest that a dramatic re-think of airport design could mitigate the emissions described above even without technological advancement in aeroplane efficiency. However, a re-think has the potential to make the travel mode zero-carbon by enabling the use of new power sources such as solar.

What are other key benefits?

  • Requiring less power to take off could aid the use of lower-density fuel types such as solar​, and the Portocielo concept could therefore pave the way for lighter, more sustainable aircraft.

  • As the Portocielo is situated several hundred meters above the ground, it is likely that less pollution would reach surface level​ than with traditional airports. (Caveat: additional research may be needed into the impact of releasing the pollutants higher in the atmosphere.)

  • Similarly, the height of the runways frees up ground space beneath it for other uses, and may help avoid the social and economic problems sometimes associated with communities in the immediate vicinity of an airport.

  • The multifunctional skyscraper pillars are designed to make airport accommodation more convenient, with rooms and pods in the same building as check-in terminals and departure lounges

  • Offers a means for nations to take independent action to reduce emissions associated with international flights

What are the proposal’s costs?

Given the elevated design of the Portocielo, it is likely that building costs would be higher than those associated with a traditional airport.

The costs of recent airport builds have varied significantly, varying between around $4.8 bn to $33 bn and upwards (Airport Technology 2015).

The Portocielo build would incur most of the costs associated with a ground-level airport, added to the costs of the skyscraper pillars, additional research and total redesign of the airport concept. 

It is important to note that, whilst the costs would undoubtedly be higher, it is possible that the long-term effects would be financially beneficial, due to the positive impact of the redesign on the environment.

Time line

We estimate 10yrs R&D and establishing a partnership for the initial Portocielo connection, 5 yrs build, and completion by 2030. Several Portocielos could be in place by 2050, with the network expanding and emissions significantly reduced.

Related proposals


Although the concept of skyscraper airports is not new, originally motivation was not related to environmental considerations:

Whilst these plans may have some major flaws, the principle of elevated runways has potential benefits for the environment, as the modern contemporaries of these designers seem to agree. Entrants for competitions of skyscraper design have presented ideas which hint at the environmental and other benefits of airport skyscrapers. The proposal here was independently arrived at but research brought up the following two references which have been used to influence our proposal vision, and have provided further ideas on the scope for elevated airport design and use:


Recent airport costs: