Diamonds in the Sky — Can We Use Nanoscience to Engineer a Cooler Planet?

Despite recent efforts to combat global climate change, we are a long way from reaching internationally recognized climate change milestones. According to the Nationals Resource Defense Council, the U.S. needs to shift its energy consumption to 80% renewable sources by 2050 to meet the goals set out by the Paris Climate Accord. While electricity generation from renewable energy is set to overtake coal in the next 10–20 years, the most recent projections by the U.S. Energy Information Administration anticipate only reaching 40% renewable energy production by 2050, well short of the Paris benchmarks, which have already been routinely criticized within the scientific community as not going far enough.[1] In fact, as of 2017, all major industrialized nations were lagging behind their climate pledges.[2]

As climate change discussions become increasingly prominent in our public discourse, more and more seemingly outlandish potential solutions are cropping up. Among these include the sequestering of carbon dioxide in rocks or the sea floor, the spraying of water or sulphate particles into the atmosphere to mimic the cooling effects of volcanic ash, or the sending of giant mirrors into orbit to reflect sunlight before it reaches earth.[3] Some of these have been harshly criticized as being unrealistic or ill-considered, but one has begun to garner serious consideration. In a previous post, I described some of the unique interactions between light and nano-sized particles, manifest as a color-changing behavior in ancient Roman dichroic glass. It turns out that these types of nanoscale particles may have implications for geoengineering as well.

Based on previous observations of large scale cooling (nearly one degree Farenheit) after the eruption of Mount Pinatubo in the Philippines in 1991, scientists have proposed injecting sulphate aerosols (released in large quantities during eruptions) into the upper atmosphere in order to mimic the cooling effects that accompany large eruptions. Sulphate particles act as scattering centers, scattering away solar radiation and thereby limiting the amount absorbed by the Earth and trapped in the atmosphere. However, this process is not without significant drawbacks. Sulphate particles may be effective at scattering light, but they also introduce a host of unwanted behaviors. Sulphates in the upper atmosphere may be converted into sulphuric acid, which may further corrode the ozone layer. Additionally, scientists note that to achieve the 2% reduction in total irradiance (light reaching the Earth) required to offset current warming trends using sulphates, the attendant scattering behavior would result in a significant increase in white light (not total) irradiation. Due to forward scattering from these particles, they may also increase the ratio of diffuse to direct radiation reaching the surface, which would be beneficial for plant growth but would limit solar cell performance; a mixed bag as far as green energy is concerned.[4]

Scientists have recently proposed injecting sulphate aerosols into the upper atmosphere to counteract global warming.

In order to circumvent the unwanted side effects of using sulphates, scientists have recently begun to suggest using nanoparticles instead. While the general idea of cooling the Earth using some scattering medium has been around for a number of years, recent studies have looked at the efficacy of the materials used, and have suggested that nanoparticles made of diamond, or nano-diamonds, may be promising candidates for cooling applications.[5,6] According to recent simulations, nano-diamond aerosols, in contrast to sulphates, would not drive ozone degradation, and would greatly limit forward scattering of light due to their high refractive indices, while producing comparable radiative forcing (the balance between sunlight absorbed by the Earth and that reflected back into space).

Nanodiamonds could prove a viable alternative to sulphates due to their inertness.

While this may sound enticing, there are a number of serious drawbacks to this method of counteracting global warming, not least of which would be the price tag. It is estimated that production of sufficient quantities of nano-diamonds to achieve a 2% reduction in total irradiance would cost in the range of $1 billion to $10 billion, though as part of a global approach this starts to look like a bargain. Perhaps more pressing is the lack of precedent for this approach. Climate scientists are rightfully hesitant to begin large scale geoengineering projects, though some intrepid experimentalists are planning field tests for later this year.

Whether nano-diamond aerosols prove to be a silver bullet in the fight against global warming, a valuable part of in a coordinated response, or a non-viable pipe dream remains to be seen. Still, it is encouraging to see creative approaches taken by climate scientists in attempting to tackle one of the largest challenges facing humanity today. While nanoscience is primarily concerned with materials and systems on the very small scale, the potential and implications of these technologies can be felt the world across. Not bad for a field that’s only been around since the 60’s.

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References:

1. Rogelj, M. den Elzen, N. Höhne, T. Frasen, H. Fekete, H. Winkler, R. Schaeffer, F. Sha, K. Riahi & M. Meinshausen, Paris Agreement climate proposals need a boost to keep warming well below 2° C, Nature 534, 631 (2016).
2. G. Victor, K. Akimoto, Y. Kaya, M. Yamaguchi, D. Cullenward & C. Hepburn, Prove Paris was more than paper promises, Nature 548, 25 (2017).
3. Schiermeir, Climate tinkeres thrash out a plan, Nature 516, 20 (2014).
4. Kravits, D.G. MacMartin & K. Caldeira, Geoengineering: Whiter skies?, Geophys. Res. Lett. 39, L11801 (2012).
5. D. Pope, P. Brasesicke, R.G. Grainger, M. Kalberer, I.M. Watson, P.J. Davidson & R.A. Cox, Stratospheric aerosol particles and solar-radiation management, Nature Clim. Change 2, 713 (2012).
6. K. Weisenstein, D.W. Keith & J.A. Dykema, Solar geoengineering using solid aerosol in the stratosphere, Atmos. Chem. Phys. 15, 11835 (2015).

View all posts by Dominik Stemer

Published November 17, 2018

Originally published at dominikstemer.wordpress.com on November 17, 2018.