“While the climate of the earth has changed over the millennia as a result of natural factors – principally changes in the tilt and orientation of the earth’s axis and rotation, and in the shape of its orbit around the sun – those changes occur far too gradually to have noticeable effects over a period of mere decades. In their current phases, moreover, they would be gradually cooling the earth – taking us to another ice age – if they weren’t being more than offset by human-caused warming.”
By the way, if this seems slightly insane to you, well that's at least in part because John Holdren is insane:
Holdren has authored numerous books and journal articles with his mentors Paul and Anne Ehrlich, the infamous doomsayers who predicted overpopulation would force most of the world's population to perish during the 1980s "great die-off."
Holdren gave a clear indication of his philosophical views in the 1977 book Ecoscience, which he co-authored with Paul and Anne Ehrlich.  In its pages, the authors noted, "The neo-Malthusiasn view proposes...population limitation and redistribution of wealth." They concluded, "On these points, we find ourselves firmly in the neo-Malthusian camp" (p. 954).
Economist Thomas Malthus is one of the most literally anti-human theorists in human history. He viewed overpopulation as the fount of all woe, but one which could be staunched with enough blood. In "An Essay on the Principle of Population" Malthus wrote, "All the children who are born, beyond what would be required to keep up the population to a desired level, must necessarily perish, unless room be made for them by the death of grown persons...if we dread the too frequent visitation of the horrid form of famine, we should sedulously encourage the other forms of destruction, which we compel nature to use...and court the return of the plague." Like their intellectual forebear, Holdren and the Ehrlichs proposed their own acceptable sacrifice to the environment.
Compulsory Abortion for American Women
The trio prescribed a rigidly enforced, government-imposed limit of two children per family. Holdren and the Ehrlichs maintained "there exists ample authority under which population growth could be regulated." Hiding behind the passive voice, they note, "it has been concluded that compulsory population-control laws, even including laws requiring compulsory abortion, could be sustained under the existing constitutionif the population crisis became sufficiently severe to endanger the society." (Emphasis added.) To underscore they mean business, they conclude, "If some individuals contribute to general social deterioration by overproducing children, and if the need is compelling, they can be required by law to exercise reproductive responsibility" (pp. 837-838). Moreover, if the United States government refuses to take proper measures, they authorize the United Nations to take compelling force.
"A Comprehensive Planetary Regime"
Holdren believed a world government might play a moderate role in the future: setting and enforcing appopriate population levels, taxing and redistributing the world's wealth, controlling the world's resources, and operating a standing World Army.
Part of the power wielded by this "Regime" would be in the form of a World Army. The trio wrote that the United States must destroy all its nuclear arsenal. But this would not render us defenseless against Communist aggression. "Security might be provided by an armed international organization, a global analogue of a police force...The first step necessarily involves partial surrender of sovereignty to an international organization" (p. 917, emphasis added).
Far from distancing himself from this wooly-headed notion as he matured, Holdren explicitly reaffirmed it in his 1995 Nobel Prize acceptance speech on behalf of Pugwash, declaiming, "The post-Cold-War world needs a more powerful United Nations, probably with a standing volunteer force -- owing loyalty directly to the UN rather than to contingents from individual nations."
Such a comprehensive Plenetary Regime could control the development, administration, conservation, and distribution of all natural resources, renewable or nonrenewable...not only in the atmosphere and oceans, but in such freshwater bodies as rivers and lakes...The Regime might also be a logical central agency for regulating all international trade...The Planetary Regime might be given responsibility for determining the optimum population for the world and for each region and for arbitrating various countries' shares within their regional limits...the Regime would have some power to enforce the agreed limits. (p. 943.)