Built-environment albedo enhancement (white roofs etc.)

Industry

The built environment takes up an ever greater portion of the earth’s surface. This mostly unused surface area could be coated in albedo enhancing paints or material which would allow them to reflect incoming sunlight.

Analysis overview

Technological Readiness Level (TRL) 3
Scalability 1
Timeliness for near-future effects 3
Northern + Arctic potential 1
Global potential 2
Cost - benefit 1
Environmental risks 3
Community impacts 3
Ease of reversibility 3
Risk of termination shock 3
Legality/governance 3
Scientific/media attention 2

Technological Readiness Level (TRL)

High 3

In many warm regions of the world it has been a longstanding custom to paint buildings white. Although certain paints or new to develop coatings might be extra efficient (See passive radiative cooling) the technology basically already exists.

Technological Readiness Level (TRL)

A technology with a TRL of 7-9: TRL 7 – prototype demonstrated; TRL 8 – system complete; TRL 9 – system proven

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Scalability

Low 1

There have been several major experiments to increase albedo over land, most infamously the attempt by Eduardo Gold, who received $200,000 to paint a mountain white in the Peruvian Andes. However, this specific measure is limited to the built environment. This means there is only a limited surface area. Moreover, although the technology already exists NASEM (2015) points to the large costs related to painting and maintenance.

Scalability

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

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Timeliness for near-future effects

High 3

Timeliness for near-future effects

Implemented in time to make a significant difference

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Northern + Arctic potential

Low 1

If all urban areas would be modified, Irivine et al (2011) found that this could lead to a 13% increase in minimum sea-ice cover. Generally though, this measure is mainly considered as effective when applied at a local scale (IPCC AR6 wg 1, 2021, chapter 4), and holds particular potential to reduce the urban heat island effect (Jacobson and Ten Hoeve, 2011). However, this would mainly be so in densely populated low latitude areas, and would be ineffective in the Arctic (Smoliak et al 2022). Moreover, since the northern regions face very cold winters, such measures might lead to increased heating requirements, and such measures should therefore be carefully considered in the North (Bright et al, 2015).

Northern + Arctic potential

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

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Global potential

Medium 2

There is general agreement that this measure would be ineffective as a measure to counter the effects of climate change on a global scale (NASEM, 2015; Lawrence et al, 2018; IPCC AR6 wg 1, 2021, chapter 4). The IPCC 2021 AR6 wg 1 report gives a global mean forcing effect of less than 0.5 W m–2 (chapter 4), and some studies see even a global net warming effect of the painting of urban roofs (Jacobson and Ten Hoeve, 2011).

Global potential

Statistically detectable impacts

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Cost - benefit

Prohibitive 1

The costs to paint and maintain a white coat of urban areas is considered to be very high, and relatively very expensive when considering the potential effect (NASEM, 2015).

Cost - benefit

Cost of investment comparable to cost of avoided damage

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Environmental risks

Low risk 3

Lawrence et al. (2018) note in their literature review that this measure might be very invasive and lead to many regional side effects.

Environmental risks

Very limited, site-specific effects restricted to the solution deployment location only

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Community impacts

Beneficial 3

Summer temperature extremes are increasingly problematic in urban areas, and this measure might thereby significantly help local communities.

Community impacts

Significant benefits to communities

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Ease of reversibility

Easy 3

NASEM (2015) considers this measure to be of 'low overall risk, and ‘easily reversible', although the painting over of white surfaces would require another major investment.

Ease of reversibility

Easily reversible naturally

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Risk of termination shock

Low risk 3

Although all SRM measures will lead to warming once it is halted, paints and similar reflective surfaces are likely to be effective for a long time, and will therefore not hold the risk of causing an abrupt warming.///

Risk of termination shock

Low or insignificant termination shock or damage

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Legality/governance

Possible 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

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Scientific/media attention

Medium 2

There is a general lack of discussion of this measure as a major climate action (Lawrence et al, 2018), although there seems to be quite some interest in it from local urban planners.

Scientific/media attention

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

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References

Bright, R. M., Zhao, K., Jackson, R. B., & Cherubini, F. (2015). Quantifying surface albedo and other direct biogeophysical climate forcings of forestry activities. Global Change Biology, 21(9), 3246-3266. https://doi.org/10.1111/gcb.12951

Irvine, P. J., Ridgwell, A., & Lunt, D. J. (2011). Climatic effects of surface albedo geoengineering. Journal of Geophysical Research: Atmospheres, 116(D24). https://doi.org/10.1029/2011JD016281

Jacobson, M. Z., & Ten Hoeve, J. E. (2012). Effects of urban surfaces and white roofs on global and regional climate. Journal of climate, 25(3), 1028-1044. https://doi.org/10.1175/JCLI-D-11-00032.1

Lawrence, M.G., Schäfer, S., Muri, H. et al. Evaluating climate geoengineering proposals in the context of the Paris Agreement temperature goals. Nat Commun 9, 3734 (2018). https://doi.org/10.1038/s41467-018-05938-3

National Academies of Sciences, Engineering, and Medicine. 2015. Climate Intervention: Reflecting Sunlight to Cool Earth. Washington, DC: The National Academies Press. https://doi.org/10.17226/18988.

Smoliak, B.V. et al 2022, Mapping potential surface contributions to reflected solar radiation Environ. Res. Commun. 4 065003. Environ. Res. Commun. 4 (2022) 065003 https://doi.org/10.1088/2515-7620/ac7a25

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