John Latham, Philip J. Rasch, Brian Launder
DOI: 10.1098/rsta.2014.0050Published 17 November 2014
Our planet is warming, largely from the ever-increasing burning of fossil fuels. If this continues, serious consequences to our planet are likely to occur within the second half of this century. The objective of Climate Engineering (hereafter CE, but also referred to as ‘Geoengineering’, and sometimes as ‘Solar Radiation Management’) is to offset the warming and some other climate consequences that would otherwise result from increasing greenhouse gas concentrations by reducing the amount of sunlight reaching the Earth’s surface or by increasing the outward transmission of long-wave radiation from the Earth. These strategies might be used throughout the period required to replace fossil-fuel burning with globally distributed clean energy and even be continued while CO2 concentrations remained too high.
Five years ago, the Royal Society published a report titled Geoengineering the Climate  summarizing many of the issues associated with CE. The Society’s article-tracking software records a large number of downloads and citations to an earlier Phil Trans A theme issue on Geoengineering  (to which a significant number of the authors involved in this Theme Issue also contributed). This fact underlines the wide scientific concern about the issues raised by global warming, and an appreciation of the urgency of charting a credible path to avoid some of its worst consequences, should efforts to shift to a very-low-carbon society progress too slowly (as appears likely). There is not yet, however, a good understanding of CE and the nuances which need to be explored.
To have any chance of developing and—should it ever be necessary—deploying a globally acceptable CE technique for temporarily countering the rising temperatures induced by continually increasing levels of atmospheric CO2 (and other contributors), there needs to be open, continuous and concerted discussion between experts and interested groups from many fields. An optimal assessment of any CE method requires a dialogue between three communities: (i) leading scientists and engineers from the arenas of meteorology, physics, chemistry, mathematics, engineering and the biological sciences to evaluate the issues from a physical point of view; (ii) experts in governance, ethics, sociology, psychology and related topics who focus on societal issues and (iii) citizens and policymakers who, in the end, must be involved in the decision on whether to deploy or not. These communities must understand the impacts, trade-offs, risks and benefits, both to the planet and to society, of the effects of CE compared with those of other choices in dealing with climate change.
This Theme Issue explores details of (i) the fundamental physics and chemistry of what we (the editors) perceive to be the most feasible of the announced CE methods; (ii) possible field experiments that can be used to examine science’s understanding of those processes and (iii) societal issues associated with the testing of CE and its impact on the planet. Indeed, the issue seeks to draw together research relevant to these disparate areas. Our primary focus is on global issues, but attention is also given to possible amelioration of significant regional-scale problems.
One important concern is that if research indicates that one or more of the CE techniques are capable of producing sufficient global cooling to offset additional heating resulting from maintaining or increasing the burning of fossil fuels, there could be a reduction of interest in reducing fossil-fuel burning. In that circumstance, climate engineering would simply be postponing the day of reckoning, with the potential for a much higher risk situation in which increasingly strong CE is required to compensate for increasingly strong CO2 forcing. Another danger is that the deployment of CE measures, while capping and perhaps reducing global temperature levels, could cause drastic and negative changes in the local weather patterns, leading, for example, to rainfall reduction in regions where precipitation levels were already marginal.