Combating heat islands with modular clouds
Our cities are heating up nearly twice the global average rate. By 2050, the urban population exposed to extreme temperatures is estimated to increase by 800 percent. This growth will yield a corresponding momentous increase in energy demand for cooling. Even at the current levels, heatwaves are the deadliest of all climate risks, while cooling systems currently account for 10 percent of global greenhouse gas emissions. Our means and methods for keeping cool are making the globe even hotter, compounding the cooling needs. Oversky is a design research project that explores the capacity of a new urban infrastructural system, leveraging passive technologies, to cool our cities. Inspired by clouds, the modular system can float over and mitigate the effect of the areas largely responsible for the urban heat island phenomenon, road networks and parking lots, reclaiming this space for people while cooling down the neighborhood.
The Gravity of Clouds. In the ancient Greek comedy, The Clouds, the philosopher Socrates declares that the Clouds are the only true deities. In the play, the clouds are hailed as masters of poetry and rhetoric, shape-shifting to reveal the true nature of whoever is looking at them.
Due to the complexity of cloud dynamics, there is still an element of mystery to the behavior of clouds. Clouds have a significant effect on the climate system through variables such as cloud cover, duration, thickness, and altitude. However, because the behavior of tiny aerosol particles largely determine these properties, clouds are notoriously difficult to simulate in models, requiring the use of proxy data in global climate models. Following new research, recent climate models have altered their treatment of clouds, uncovering alarming findings . The new predictions overturn a long established consensus about the climate sensitivity of the planet. While most leading climate models still correlate a doubling of CO in the atmosphere to a 1 degree C global temperature increase, the matter is complicated by a series of external variables. There are three primary feedback mechanisms caused by the natural systems in response to initial warming: the melting of ice and snow; the additional atmospheric water vapor; and, the most uncertain, the behavior of clouds.
'Skyer', Niclas Gulbrandsen.
We generally think of clouds as keeping us cool, but this is not always the case. Clouds such as Marine Stratus and Stratocumulus shade roughly one fifth of the oceans, cooling the Earth by reflecting solar radiation that hits them back into space. The higher Cirrus clouds, on the other hand, are thin enough to let sunlight through while preventing heat from escaping as infrared radiation, effectively acting as insulating blankets. As a general rule, low, thick clouds reflect sunlight, while high, thin clouds trap heat below them. It has been determined that a warming Earth will push clouds upward and poleward, allowing for more solar energy to warm the earth . Researchers at Caltech have argued that global cloud cover may have a tipping point, beyond which clouds would “become unstable and break up,” sending global warming into overdrive.
The cloud formations connect to the street below and link adjacent city blocks, complementing the ordered grid of the city with an adaptable, three-dimensional connective tissue
Hot in the City. Without reductions in greenhouse gas emissions, heat will continuously build up in our atmosphere. This causes a cascading catastrophe of environmental chaos. Heat absorbs the moisture from the soil, which leads to less evaporation. This leads to less cloud cover and more sun, creating a vicious feedback cycle of heat, drought and fire. The climate crisis amplifies this cycle, making these natural disasters longer, more intense, and more frequent.
Climate models have historically lacked an accurate representation of urban areas at a global scale. In 2021, a team of researchers created a new model that includes comprehensive climate projections for cities, suggesting that hotter cities could be devastating for urban public health . In a “business as usual” scenario, cities could warm as much as 4.4 degree C by the year 2100. Even in a scenario of substantial mitigation of greenhouse gas emissions, a large number of cities will experience warming of more than 1.5 degree C, the target set by the Paris Agreement. According to the WHO, heatwaves are among the most dangerous of natural hazards, but rarely receive adequate attention because their death tolls and destruction are not always immediately obvious. Between 2000 and 2016, the number of people exposed to heat waves increased by 125 million .
Cities make up less than 3 percent of the land area of the earth, yet accommodate more than half of its population. The climate in urban areas is distinctly different from that in surrounding rural areas, due to what is known as the heat island effect. This condition is a consequence of how cities have been designed, as tall buildings, paved roads, and other infrastructure absorb and release the heat of the sun. The contemporary city is engineered for efficiency and density, largely divorced from the presence and processes of nature. In its place, a high density of heat exchange systems further contribute to the warmer urban climates. The majority of open space in the city is inaccessible to people and strictly delineated for vehicular transit and parking. This network of concrete and asphalt jeopardizes the quantity and quality of public space, with only a few plazas, parks, and green patches scattered across the city. The open space of the contemporary city is by and large the right of engines, not people.
The outer skin of the modules is engineered to reflect heat back into space while absorbing almost no radiation, effectively maintaining a significantly lower surface temperature than the surrounding environment.
The system is designed to reduce heat buildup in cities by reflecting solar radiation through passive radiative cooling and evaporative cooling.
A Cool Intervention. Oversky is a project that seeks to intervene in this scenario, reducing heat buildup in cities while reclaiming space for people from the vast areas given up to vehicles and infrastructure. The project consists of a modular system of volumes that can float within urban chasms, forming space for public imagination and expression. The formations connect to the street below and link adjacent city blocks, complementing the ordered grid of the city with an adaptable, three-dimensional connective tissue. Modular archipelagos of space form cultural centers, classrooms, art studios, offices, and cinemas, responding to local needs of neighborhoods while giving the city back space lost to transit networks – space that invigorates city energy, culture, and collective activities.
The structure is designed to form cloud-like clusters, providing shaded microclimates for the city by reflecting heat from the sun. The coating of the modules makes use of a technique called radiative cooling. Through nanophotonic engineering, a foam-like material structure with nanoscale air pockets is designed to reflect sunlight and radiation in a narrow band of the light spectrum. The wavelengths of this band correspond to a “transmission window” in the atmosphere, allowing heat to escape into outer space and cool down the surface to below its surrounding temperature, even in full sunlight. A team of researchers have demonstrated that panels placed under direct sunlight remained 4.9 degrees C below air temperature, providing a “cooling power of 40.1 watts per square meter” . (Another study demonstrated that a temperature reduction of up to 42 degrees C is possible .) The geometry of the structure is designed to channel and collect rain water. With the use of a hydronic radiant cooling system, the water gets circulated through a network of thin pipes running underneath the skin, cooling down its interior and – through the integration with existing cooling infrastructure – neighboring buildings. Water is also released as fine mist on the underside of the structure, enabling the cloud to remove additional heat from the street environment through evaporative cooling. In addition, the use of a titanium dioxide coating enables the outer surface to clean the air through the break-down of airborne pollutants. The geometry of the underside of the cloud is designed to combat a different kind of pollution, as it absorbs noise from the traffic below.
The system is intended to reclaim space for people from the vast areas given up to vehicles and infrastructure in cities.
The kit-of-parts consist of five cloud modules in addition to a series of distinct infrastructural links, connecting the streetscape below with the cloudscape above.
The Legacy of Zeppelin. In 1937, while preparing to land at the Lakehurst Naval Air Station in New Jersey, the Hindenburg airship burst into flames and crashed to the ground. This disaster shattered public confidence in the airship and marked the end of a brief, glorious era of the commercial airship. However, the technology for these lighter-than-air (LTA) vehicles has seen an ongoing development since then. Today, as the airship is seeing renewed interest from companies and governments around the world, the core technology is safer, more advanced, more affordable, and has a smaller carbon footprint.
LTA technology serves as the backbone of the Oversky modules. Rigid frames of carbon fiber create strong, light-weight enclosures for cells of Helium lift-gas (instead of Hydrogen, which due to its flammability limit, was the cause of the Hindenburg explosion). In accordance with Archimedes’ principle, the structure levitates on the principle of buoyancy. The structure generates a lift equal to the weight of the displaced air, minus the weight of the structure. In addition, the interconnected modules are supported with a set of distinct infrastructural links, connecting the streetscape below with the cloudscape above. These links are designed to celebrate the entry points, while activating the street through various functional and programmatic contributions, from playgrounds and parks to pop-up restaurants.
| Public Space Modules
| Lift-gas Modules
| Cloudscape Garden
| Streetery Link
| Access Link
| Misty Environment
| Air Movement & Stack Effect
| Shaded Microclimate
| Reflected Solar Radiation
The Heating of Cooling. Our efforts to keep space, food, data, and industry cool comes at a high energy cost. Over the last 20 years, Europe has seen a 20-fold increase in energy cooling needs, largely driven by the increase in living and working standards . As the planet is heating up and a large part of the global population is seeking higher comfort standards, the demand for cooling will grow fast, particularly in the so-called developing world. This growth is estimated to require a threefold increase in the global energy use, reaching 6,200 terawatt-hours by 2050 , and will contribute to a significant portion of the global heat-trapping gas emissions. The majority of current cooling technology ironically exacerbates the very issue it seeks to mitigate. A warming planet will also stress our infrastructure for cooling. Power plants and air-conditioning units will become less efficient, power lines will have lower capacities, and hardware like transformers will experience more failures, which can cause power blackouts when we need cooling the most.
It is important to underscore that Oversky is a speculative project that seeks to explore alternative, zero-emission means to keep our cities cool. The system is not proposed as a silver bullet solution, but rather, imagined to form part of a city’s greater resilience and heat mitigation strategy. Such a strategy needs to include comprehensive plans for increasing the city’s blue and green infrastructure; be sensitive to the heat vulnerability of its neighborhoods; and work alongside a host of measures to address the root causes of the environment crisis.
As we enter a decisive decade for addressing the climate crisis, our need for cooling is at risk of becoming one of the key obstacles to making meaningful global progress. Cooling represents one of the most insidious challenges of the crisis, as well as being one of the hardest technological problems to solve. Confronted with existential risk, it is not enough to merely pursue incremental improvement of current models and technologies. Radical projects, such as Oversky, serve the important role of calling attention to alternative solutions and can help galvanize a transition towards a new paradigm that combines the continued development of human societies and the maintenance of the Earth System in a resilient and accommodating state, before it is too late.
Photo by the amazing Lerone Pieters
1. Pearce, F., Why Clouds Are the Key to New Troubling Projections on Warming. Yale Environment 360, Yale School of the Environment, February 5, 2020, https://e360.yale.edu/features/why-clouds-are-the-key-to-new-troubling-projections-on-warming
2. Norris, J., Allen, R., Evan, A. et al. Evidence for climate change in the satellite cloud record. Nature 536, 72–75 (2016). https://doi.org/10.1038/nature18273
3. Schneider, T., Kaul, C.M. & Pressel, K.G. Possible climate transitions from breakup of stratocumulus decks under greenhouse warming. Nat. Geosci. 12, 163–167 (2019). https://doi.org/10.1038/s41561-019-0310-1
4. Zhao, L., Oleson, K., Bou-Zeid, E. et al. Global multi-model projections of local urban climates. Nat. Clim. Chang. 11, 152–157 (2021). https://doi.org/10.1038/s41558-020-00958-8
5. Watts, N., Amann, M., Arnell, N., et al. The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises. Lancet. 2021 Jan 9;397(10269):129-170. doi: 10.1016/S0140-6736(20)32290-X. Epub 2020 Dec 2. Erratum in: Lancet. 2020 Dec 14;: PMID: 33278353.
6. Skyer, Niclas Gulbrandsen. Illustration for H. Holm, "Soga um kapergastane og deira våde-råm", Oslo 1968. The National Museum of Art, Architecture and Design, Norway
7. Chen, Z., Zhu, L., Raman, A. et al. Radiative cooling to deep sub-freezing temperatures through a 24-h day–night cycle. Nat Commun 7, 13729 (2016). https://doi.org/10.1038/ncomms13729
8. Wehner, M. The effect of anthropogenic climate change on heat waves in the United States. Retrieved August 25, 2021 from https://crd.lbl.gov/assets/Uploads/CONUS-2021-heat-wave-attribution-statement-071221.pdf
9. IEA (2018), The Future of Cooling, IEA, Paris https://www.iea.org/reports/the-future-of-cooling
10. Pacheco-Torgal, F. & Labrincha, J.A. & Cabeza, Luisa F. & Granqvist, Claes. (2015). Eco-efficient materials for mitigating building cooling needs: Design, properties and applications.
11. Raman, A., Anoma, M., Zhu, L. et al. Passive radiative cooling below ambient air temperature under direct sunlight. Nature 515, 540–544 (2014). https://doi.org/10.1038/nature13883
Granqvist, C. and G. Niklasson. “Solar energy materials for thermal applications: A primer.” Solar Energy Materials and Solar Cells 180 (2018): 213-226.
Fan, Shanhui & Raman, Aaswath. (2018). Metamaterials for radiative sky cooling. National Science Review. 5. 132-133. 10.1093/nsr/nwy012.
Mandal J, Fu Y, Overvig AC, Jia M, Sun K, Shi NN, Zhou H, Xiao X, Yu N, Yang Y. Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling. Science. 2018 Oct 19;362(6412):315-319. doi: 10.1126/science.aat9513. Epub 2018 Sep 27. PMID: 30262632.
Mandal et al., Paints as a Scalable and Effective Radiative Cooling Technology for Buildings, Joule (2020), https://doi.org/10.1016/j.joule.2020.04.010
Rockström, J. "Bounding the Planetary Future: Why We Need a Great Transition," Great Transition Initiative (April 2015), http://www.greattransition.org/publication/bounding-the-planetary-future-why-we-need-a-great-transition.
Granqvist, C. G. & Hjortsberg, A. Radiative cooling to low temperatures: general considerations and application to selectively emitting SiO films. J. Appl. Phys. 52, 4205–4220 (1981)
Goldstein, E., Raman, A. & Fan, S. Sub-ambient non-evaporative fluid cooling with the sky. Nat Energy 2, 17143 (2017). https://doi.org/10.1038/nenergy.2017.143