Radiative covering and building technologies/ Passive daytime radiative cooling

Industry

An increase in GHGs in the atmosphere leads to a greater amount of outgoing infrared radiation from the earth being retained. There are several ideas to reduce the resulting warming by modifying surface radiation processes.

Passive daytime radiative cooling (PDRC) promises to provide energy free cooling through thermally-emissive surfaces that reflect incoming solar radiation whilst simultaneously enhancing longwave heat transfer to space through the infrared window of the atmosphere (8–13 µm) (Yin et al. 2020). The technology is relatively novel, and has seen rapid growth over the last couple of years (Khan, 2022). Several different variants exist that all have slightly different properties, but generally share a layered structure which allows for its shortwave reflective and longwave emissive properties, whilst not letting heat through. Some of PDRC advocates have described it as a ‘third, less intrusive geoengineering approach’ (Zevenhoven and Fält 2018). Probably PDRC should however not be grouped under the category geoengineering (see for differing categorisations of geoengineering: Heyward 2013; or Pereira 2016).

Technological Readiness Level (TRL)

Medium 2

These materials are currently being developed in material and laboratory tests.

Technological Readiness Level (TRL)

A technology with a TRL of 4-6: TRL 4 – validated in lab; TRL 5 – validated in relevant environment; TRL 6 – demonstrated in relevant environment

Scalability

Low 1

Such materials are likely to be most effective in the built environment, which would make them less applicable to the Arctic (see also urban albedo enhancement).

Scalability

Physically unable to scale; sub-linear/logarithmic efficiency of scalability

Timeliness for near-future effects

High 3

Many of these new materials are already in use, whilst new ones are being developed.

Timeliness for near-future effects

Implemented in time to make a significant difference

Northern + Arctic potential

Low 1

Although PDRC is held up as a great promise for urban areas in temperate or desert environments, its potential for northern and Arctic regions could be limited (Yin et al, 2020). Combined with the lack of built environment to apply PDRC on, there would be serious issues with overcooling in winter, although Khan et al (2022) suggest this might be compensated for by installing switchable coatings. Li et al (2022) suggest that this technology might be used to prevent ice from melting, and it might in the future be feasible that it could be used on particularly valuable glaciers (see glacier covering), however, these would be equally limited in scalability and therefore global impactfulness.

Northern + Arctic potential

No noticeable extra positive effect beyond the global average; technology is unsuited to the Arctic

Global potential

Low 1

Global potential

Insignificant to be detected at a global scale

Cost - benefit

High 1

Cost - benefit

Cost of investment comparable to cost of avoided damage

Environmental risks

Medium 2

Environmental risks

More widespread and possibly regional impacts that extend beyond the immediate solution deployment location

Community impacts

Neutral 2

Community impacts

Unnoticeable or negligible positive or negative effects

Ease of reversibility

Hard 1

Ease of reversibility

Impossible or very difficult to reverse

Risk of termination shock

Low 3

Risk of termination shock

Low or insignificant termination shock or damage

Legality/governance

High 3

It is likely that nation states could implement such measures on their own territory.

Legality/governance

Currently legal to deploy, with governance structures in place to facilitate it and/or financial incentives to develop it

Scientific/media attention

Medium 2

There seems to be an increase in scientific papers and commercial applications that is mainly centered in China.

Scientific/media attention

Some attention within the scientific community, including published research and funding programmes; some media attention; some commercial interest

References

Khan, Ansar; Carlosena, Laura; Feng, Jie; Khorat, Samiran; Khatun, Rupali; Doan, Quang-Van; Santamouris, Mattheos (2022). "Optically Modulated Passive Broadband Daytime Radiative Cooling Materials Can Cool Cities in Summer and Heat Cities in Winter". Sustainability. 14 – via MDPI. https://doi.org/10.3390/su14031110

Levinson, Ronnen, et al. 2019. Solar-Reflective “Cool” Walls: Benefits, Technologies, and Implementation. No. LBNL-2001296; AWD-00002242; CEC-500-2019-040. Lawrence Berkeley National Lab.(LBNL), Berkeley, CA (United States). Available at: https://www.energy.ca.gov/publications/2019/solar-reflective-cool-walls-benefits-technologies-and-implementation [Accessed 22 July 2024]

Li, J., Liang, Y., Li, W., Xu, N., Zhu, B., Wu, Z., ... & Zhu, J. (2022). Protecting ice from melting under sunlight via radiative cooling. Science advances, 8(6), eabj9756. https://doi.org/10.1126/sciadv.abj9756

Yin, Xiaobo; Yang, Ronggui; Tan, Gang; Fan, Shanhui. (2020). "Terrestrial radiative cooling: Using the cold universe as a renewable and sustainable energy source". Science. 370 (6518): 786–791. https://doi.org/10.1126/science.abb0971

Zevenhovena, Ron and Fält, Martin. (2018). Radiative cooling through the atmospheric window: A third, less intrusive geoengineering approach. Energy. 152. https://doi.org/10.1016/j.energy.2018.03.084

Related ideas

Industry

Radiative covering and building technologies/ Passive daytime radiative cooling

Mountain pine and spruce forest in winter, Hillestadheia, Norway

Atmosphere / solar radiation

Snowfall enhancement

With the exception of some regions like Antarctica, global snowfall amount and frequency have decreased, and the timespan during which snow cover remains has shortened (Zender 2012). This has multiple effects on human and natural systems as it influences widely diverging processes such as reducing surface albedo and changes in the hydrological cycle.

Shelf-Iceberg, North of Antarctic Peninsula

Ice sheets and glaciers

Ice sheet stabilization via buttressing

One of the potentially most catastrophic effects of contemporary global warming would be the dramatic increase in sea levels as a result of the melting Greenland and Antarctic ice sheets. Even if all current emissions were immediately stopped, sea level rise could still occur because of lockedin warming (State of the Cryosphere report 2022).

Cultivating algae for export to Japan, Zanzibar

Oceans & marine

Seaweed and macro algae cultivation

The potential of carbon sequestration by marine based plants such as mangroves, seagrass and algae, often referred to as blue carbon, and the importance of better understanding it, has clearly been recognised (Mcleod et al. 2011). The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (2019) concluded blue carbon can play an important role in both climate regulation and adaptation. The term algae groups together several kinds of marine photosynthetic organisms. These are often subdivided into very small microalgae like phytoplankton, and larger macroalgae like kelp and seaweed. Although there is still large uncertainty about the total amount of carbon sequestered by these marine organisms, a recent estimate by Duarte et al. (2022) indicated that all macroalgae took in as much CO2 as the Amazon rainforest.

Ice sheets and glaciers

Ice sheet stabilization by draining water or bed freezing

Polar bear looking for whale cadaver under water, Svalbard

Industry

Direct ocean capture

The majority of the inorganic carbon on Earth is stored in the oceans. There is a natural carbon exchange between the ocean and the land.

Ice sheets and glaciers

Glacier albedo increase

Up to 50% of the world’s glaciers are set to disappear this century, with many more at risk if emission reduction targets are not met (Rounce et al. 2023). The surface of many mountain glaciers has moreover significantly darkened due to a general increase in atmospheric black carbon and other kinds of aerosols.

Oceans & marine

Re-oxygenating the Baltic

The deep waters in the Baltic are severely deoxygenated. Although the causes of the current state are complex, this is mainly a result of increased eutrophication from sewage and agricultural runoff from surrounding lands, which leads to extreme bioproductivity (Rolff et al. 2022). Some species manage to survive in the upper water layers, but many organisms living on the seafloor are severely impacted by the hypoxia, thereby influencing the health of a wide network of ecosystems and biochemical processes. There are attempts to reduce nutrient runoff into the Baltic (see for example: https://helcom.fi/baltic-sea-action-plan/). However, some argue these will be insufficient and argue for engineering solutions to the issue.