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The Earth is now recognized as a self-regulating system that includes a reactive biosphere; the system maintains a long-term steady-state climate and surface chemical composition favourable for life. We are perturbing the steady state by changing the land surface from mainly forests to farm land and by adding greenhouse gases and aerosol pollutants to the air. We appear to have exceeded the natural capacity to counter our perturbation and consequently the system is changing to a new and as yet unknown but probably adverse state. I suggest here that we regard the Earth as a physiological system and consider amelioration techniques, geoengineering, as comparable to nineteenth century medicine.

Organisms change their world locally for purely personal selfish reasons; if the advantage conferred by the ‘engineering’ is sufficiently favourable, it allows them and their environment to expand until dominant on a planetary scale.

Our use of fires as a biocide to clear land of natural forests and replace them with farmland was our second act of geoengineering; together these acts have led the Earth to evolve to its current state. As a consequence, most of us are now urban and our environment is an artefact of engineering.

according to the United Nations’ Intergovernmental Panel on Climate Change, the cooling effect of white particles may counteract as much as about half of the warming effect of carbon dioxide. So, if all white particles were removed from the atmosphere, global warming would increase considerably.CommentsView/Create comment on this paragraphThe dilemma is that all particles, whether white or black, constitute a serious problem for human health. Every year, an estimated two million people worldwide die prematurely, owing to the effects of breathing polluted air. Furthermore, sulfur-rich white particles contribute to the acidification of soil and water.

Naturally, measures targeting soot and other short-lived particles must not undermine efforts to reduce CO2 emissions. In the long term, emissions of CO2 and other long-lived greenhouse gases constitute the main problem. But a reduction in emissions of soot (and other short-lived climate pollutants) could alleviate the pressures on the climate in the coming decades.

what do we do about white particles? How do we weigh improved health and reduced mortality rates for hundreds of thousands of people against the serious consequences of global warming?CommentsView/Create comment on this paragraphIt is difficult to imagine that any country’s officials would knowingly submit their population to higher health risks by not acting to reduce white particles solely because they counteract global warming. On the contrary, sulfur emissions have been reduced over the last few decades in both Europe and North America, owing to a desire to promote health and counter acidification; and China, too, seems to be taking measures to reduce sulfur emissions and improve the country’s terrible air quality. But, in other parts of the world where industrialization is accelerating, sulfur emissions continue to increase.