Built-environment albedo enhancement (white roofs etc.)

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 SRM ideas that seek to compensate for this by reflecting more radiation back to space.

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.

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

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

Timeliness for near-future effects

High 3

Timeliness for near-future effects

Implemented in time to make a significant difference

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

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

Cost - benefit

High 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

Environmental risks

Low 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

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

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

Risk of termination shock

Low 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

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 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

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

Related ideas

Alternating layers of limestone and dolomite, Eleonore Bay, Northeast Greenland National Park

Industry

Atmospheric methane capture by zeolites

Methane is a highly potent greenhouse gas and its reduction is given ever greater priority in international emission reduction policies (see for example https://www.globalmethanepledge.org/). There are many different materials that have been suggested and explored to capture methane (Alonso et al. 2017).

High Arctic Tundra, Northern Taymyr, Russia July 1990

Industry

Methane flaring (not industrial)

Methane is a highly potent greenhouse gas and its reduction is given ever greater priority in international emission reduction policies. Given the increasing, and potentially catastrophic rate of methane release from the thawing Arctic and Northern permafrost, these regions are crucial in this endeavor. Apart from the methane release from microbial activity in thawing permafrost on land, methane also escapes in the form of hydrates which have been formed under sediments beneath the sea.

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).

Clouds over peaks in Uummannaq, Greenland

Atmosphere / solar radiation

Arctic winter high-latitude seasonal stratospheric aerosol injection

GHG emissions reductions and future negative emissions are the only sustainable solutions to stabilize or even reverse global warming as they counter the cause of the problem. However, the required actions will likely take time to materialize, and inertia in the climate system and locked-in warming already ensures major changes in global temperatures and the nearing of several tipping points. Solar radiation management (SRM) techniques seek to reduce global temperatures by reflecting incoming solar radiation. They would thereby not fix the underlying issue of the warming effects of GHGs but are, according to the United Nations Environment Programme (UNEP) Review on Solar Radiation Modification Research (2023), 'the only known approach that could be used to cool the Earth within a few years'.

River Ölfusá just North of Selfoss, South Iceland

Oceans & marine

River Liming

The pH of water is lowered when it takes up atmospheric carbon. Given that the Earth’s oceans serve as a major carbon sink, there is increasing interest in the possibility to artificially increase the alkalinity of water to restore pH to previous levels, and/or increase carbon uptake potential.

Industry

Atmospheric Methane destruction: Tropospheric iron salt aerosol injection

A school of juveniles of the Dusky spinefoot Siganus luridus (second)

Oceans & marine

Artificial upwelling

Oceans play an important role in global heat transfer and carbon storage processes. As global temperatures and atmospheric carbon levels rise, some have suggested artificially modifying the vertical movement of water to enhance these processes.

Ice sheets and glaciers

Increasing glacier thickness by local artificial snow production

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).