A Case for Climate Engineering

2 Climate Risk

2 Climate Risk James Hansen, the world’s most visible climate-scientist turned activist, has said that we must stop development of the Canadian tar sands, a growing source of energy-intensive oil production , or else, “It’s game over for the planet.”8 I share Hansen’s opposition to tar sands development, but I see no scientific basis to make such claims of imminent doom. Predictions of catastrophe are more than rhetorical flourishes. They appeal to widely shared concerns that industrial civilization has lost its way, millennial fears that overconsumption is leading us to an environmental apocalypse that would be nature’s ultimate act of retribution against a misguided species. a case for climate engineering  Our climate choices would be easy if we were truly facing an imminent existential threat. Emergencies entail extreme measures, a narrow focus on a single problem that may justify suspension of democratic due process. Imagine how effectively the world might collaborate if we discovered a massive asteroid inbound for a 2050 impact. But, this is not what we face. The claim that climate change threatens an imminent catastrophe is an attempt to play a trump card of (seemingly) objective science in order to avoid debate about the trade-offs at the heart of climate policy and about the role that values play in driving each of our personal judgments of the moral weight we accord to competing interests. But climate change is one of many problems, so there is no substitute for realistic assessment of our risks and open debate about the trade-offs between them, for we cannot avoid all risk or solve all problems. If there is no imminent existential threat, why do we want to stop climate change? Because climate risks are serious. While it’s true that change is the only con- david keith  stant in the long evolution of the earth’s climate, industrial humanity has become a geological force driven change at unprecedented rates. Combustion of fossil fuels has raised carbon dioxide to levels not seen for millions of years. And the pace is accelerating; roughly half of all the carbon dioxide emitted in human history was emitted in the last quarter century. If we continue on our present course, within this century—within the lifetime of my children—human actions may well push carbon dioxide concentrations to levels not seen since the Eocene, the last period in which geoscientists are confident that carbon dioxide concentrations stood above 1,000 parts per million, about four times their pre-industrial value of about 270 parts per million.The Eocene was an era in the geologic record that ended about thirty-five million years ago, an era in which crocodilians walked the shores of Axel Heiberg Island in the present-day Canadian Arctic. Global emissions of carbon dioxide now exceed thirty billion metric tons per year, an average of five tons per capita. An average American is responsible a case for climate engineering  for about twenty tons, four times the global average. This is a big number, the weight of about ten cars for each person each year. The mass of carbon dioxide we dispose of in the atmosphere dwarfs by a factor of forty the mass of garbage we send to landfills. It now exceeds all human-driven material flows, including the gigantic movements of mine overburden. If carbon dioxide were garbage—a smelly mass that had to be pushed around with bulldozers—we would have dealt with this problem long ago. The root of the climate threat is that humanity is moving carbon from deep geological reservoirs to the biosphere approximately a hundred times faster than the corresponding natural process in which carbon escapes from the Earth’s crust at locations such as volcanic vents. While significant uncertainty remains about the climate’s sensitivity to increasing carbon dioxide and about the attribution of recent warming to the historical increase in carbon dioxide, the unprecedented human acceleration of the carbon cycle is an undisputed fact. david keith  We cannot accurately predict the results of our uncontrolled “experiment” on our planet, but it is certain that if we continue on our present course we are committing our children to climate changes that will be extraordinarily rapid compared to those humanity has experienced over the ten millennia since the invention of agriculture, when carbon dioxide concentrations stayed...