If geo-engineering is defined as purposeful human activity that significantly alters the state of the Earth, we became geo-engineers soon after our species started using fire, for cooking, land clearance and smelting bronze and iron. There was nothing unnatural in this; other organisms have been massively changing the Earth since life began 3.5 Gyr ago. Without oxygen from photosynthesizers, there would be no fires. Morton (2007) in his remarkable book Eating the Sun describes the crucial role of these organisms in shaping the evolution of the Earth and its climate.

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.

Geo-Engineering Climate Change: Environmental Necessity or Pandora's Box?, eds. Brian Launder and Michael Thompson. Published by Cambridge University Press. © Cambridge University Press 2010.

Our use of fires as a biocide to clear land of natural forests and replace them with farmland was our second act of geo-engineering; 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. During this long engineering apprenticeship, we changed the Earth, but until quite recently, like the photosynthesizers, we were unaware that we were doing it, still less the adverse consequences.

It might seem that the Fourth Assessment Report of the IPCC (2007) by over 1000 of the world's most able climate scientists would provide us with most of what we need to know to ameliorate adverse climate change. Unfortunately, it does not; the conclusions so far are tentative and preliminary. The gaps that exist in our knowledge about the state of the oceans, the cryosphere and even the clouds and aerosols of the atmosphere make prediction unreal. The response of the biosphere to climate and compositional change is even less well understood; most of all, we are ignorant about the Earth as a self-regulating system and only just beginning to recognize that many separate but connected subsystems exist that can exert positive and negative feedback on a global scale. It was not until 2001 that the Amsterdam Declaration stated as follows: the Earth system is a self-regulating system comprising the atmosphere, oceans and surface rocks and all of the organisms, including humans. Earth system science is acknowledged, but like a new book that one day we will read, it stays on the shelf. Consequently, the climate models of the IPCC are still based on atmospheric physics and the programs of their models do not yet include the code needed for a self-regulating Earth. Land and ocean surface changes are touched on but mainly from the viewpoint of their passive effect on the atmosphere. Even Lenton's (2006) review of climate change to the end of the millennium still appears to view the climate as mainly determined by geophysics. This concentration on atmospheric physics is a natural consequence of the evolution of climate science from weather forecasting, but most of all this is because there has been neither the time nor the resources to do more. We may soon need to try geo-engineering because careful observation and measurement show that climate is changing faster than forecast by the gloomiest of the IPCC models (Rahmstorf et al. 2007).

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