First formulated by Lovelock during the 1960s as a result of work for NASA concerned with detecting life on Mars,[18] the Gaia hypothesis proposes that living and non-living parts of the Earth form a complex interacting system that can be thought of as a single organism.[19][20] Named after the Greek goddess Gaia at the suggestion of novelist William Golding,[15] the hypothesis postulates that the biosphere has a regulatory effect on the Earth's environment that acts to sustain life.
While the Gaia hypothesis was readily accepted by many in the environmentalist community, it has not been widely accepted within the scientific community. Among its more famous critics are the evolutionary biologists Richard Dawkins, Ford Doolittle, and Stephen Jay Gould – notable, given the diversity of this trio's views on other scientific matters. These (and other) critics have questioned how natural selection operating on individual organisms can lead to the evolution of planetary-scale homeostasis.[21] Lovelock has responded to these criticisms with models such asDaisyworld, that illustrate how individual-level effects can translate to planetary homeostasis, under the right circumstances.
In Lovelock's 2006 book, The Revenge of Gaia, he argues that the lack of respect humans have had for Gaia, through the damage done to rainforests and the reduction in planetary biodiversity, is testing Gaia's capacity to minimize the effects of the addition of greenhouse gases in the atmosphere. This eliminates the planet's negative feedbacks and increases the likelihood ofhomeostatic positive feedback potential associated with runaway global warming. Similarly the warming of the oceans is extending the oceanic thermocline layer of tropical oceans into the Arcticand Antarctic waters, preventing the rise of oceanic nutrients into the surface waters and eliminating the algal blooms of phytoplankton on which oceanic food chains depend. As phytoplankton and forests are the main ways in which Gaia draws down greenhouse gases, particularly carbon dioxide, taking it out of the atmosphere, the elimination of this environmental buffering will see, according to Lovelock, most of the earth becoming uninhabitable for humans and other life-forms by the middle of this century, with a massive extension of tropical deserts.
In his most recent book, "The Vanishing Face of Gaia",[22] he rejects scientific modelling that disagrees with the scientific findings that sea levels are rising faster, and Arctic ice is melting faster, than the models predict and he suggests that we may already be beyond the tipping point of terrestrial climate into a permanently hot state. Given these conditions, Lovelock expects humancivilization will be hard pressed to survive. He expects the change to be similar to the Paleocene-Eocene Thermal Maximum when atmospheric concentration of CO2 was 450 ppm. At that point the Arctic Ocean was 23 °C and had crocodiles in it,[23][24] with the rest of the world mostly scrub and desert.