Stratospheric aerosol particles and solar-radiation management

Journal name:
Nature Climate Change
Volume:
2,
Pages:
713–719
Year published:
DOI:
doi:10.1038/nclimate1528
Received
Accepted
Published online

Abstract

The deliberate injection of particles into the stratosphere has been suggested as a possible geoengineering scheme to mitigate the global warming aspect of climate change. Injected particles scatter solar radiation back to space and thus reduce the radiative balance of Earth. Previous studies investigating this scheme have focused primarily on sulphuric acid particles to mimic volcanic injections of stratospheric aerosol. However, the composition and size of volcanic sulphuric acid particles are far from optimal for scattering solar radiation. We show that aerosols with other compositions, such as minerals, could be used to dramatically increase the amount of light scatter achieved on a per mass basis, thereby reducing the particle mass required for injection. The chemical consequences of injecting such particles into the stratosphere are discussed with regard to the fate of the ozone layer. Research questions are identified with which to assess the feasibility of such geoengineering schemes.

At a glance

Figures

  1. The stratospheric injection of particles will perturb the atmospheric radiative budget and the chemistry of the atmosphere.
    Figure 1: The stratospheric injection of particles will perturb the atmospheric radiative budget and the chemistry of the atmosphere.

    The quantitative effect of the injection will depend on the aerosol composition, size, and location and altitude of injection.

  2. Change in Bond albedo from a 1-km-thick stratospheric layer of aerosol whose size distribution is log-normal and whose volume fraction is held constant (equivalent to one 1-[mu]m-radius droplet per cm3 of air).
    Figure 2: Change in Bond albedo from a 1-km-thick stratospheric layer of aerosol whose size distribution is log-normal and whose volume fraction is held constant (equivalent to one 1-μm-radius droplet per cm3 of air).

    This figure identifies the optimal size and composition of a monodisperse population of particles for scattering solar radiation. If the particles are assumed to have the same radii and be spherical then the maximum change in Bond albedo (ΔA) occurs at a particle size of about 0.1 μm and refractive index of about 3.4. For the more realistic log-normal distribution the maximum change occurs at a particle size of about 0.1 μm and refractive index of about 2.96. The albedo calculations for Fig. 2 and Supplementary Fig. S1 have assumed the ability to create and maintain desired aerosol size distributions. The microphysical processes that determine the evolution of the size distribution (for example, coagulation, sedimentation, condensation or evaporation)53 were not considered. It is likely that the injected size distribution is an initial state that evolves to different steady-state size distributions than are used here. These processes have been shown to occur in the stratospheric aerosol population subsequent to the Pinatubo eruption53. The radiation calculations assume the particles are evenly spread over the whole Earth. In reality global circulation will make the particle distribution inhomogeneous54.

  3. Temperature and humidity conditions relevant for stratospheric particle chemistry in SRM schemes.
    Figure 3: Temperature and humidity conditions relevant for stratospheric particle chemistry in SRM schemes.

    a–d, Height (a), temperature (b) specific humidity (c) and relative humidity (d) of the 50 hPa (0.05 bar) surface as a function of latitude. In all panels the black line is the long-term annual mean from 1989 to 2009, the red line is the maximum monthly mean and the blue line is the minimum monthly mean over this period. Data from the ERA-Interim data set (www.ecmwf.int)55.

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Affiliations

  1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

    • F. D. Pope
  2. NCAS/Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK

    • F. D. Pope,
    • P. Braesicke,
    • M. Kalberer &
    • R. A. Cox
  3. Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK

    • R. G. Grainger
  4. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK

    • I. M. Watson
  5. Davidson Technology Limited, 8a Village Walk, Onchan, Isle of Man IM3 4EA, UK

    • P. J. Davidson

Competing financial interests

P.J.D. is employed by Davidson Technology Limited, the company holding the patent application mentioned in ref. 15.

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