But sometimes when a corner gets turned, another, sharper corner shows itself. Even if carbon emissions were dramatically reduced all over the planet (including in China, India, and Africa, where fossil fuel engines are just firing up), the biosphere is already facing catastrophe. The greenhouse effect is self-compounding, and scientists tell us that atmospheric temperatures will continue to rise even without more pollution. However difficult it has been to launch a real discussion of the causes of global warming, an even-larger controversy looms now, as problematic attempts to mitigate warming through "geoengineering" are forced onto the human agenda.

So perhaps this unprecedented problem will finally be meaningfully addressed by the president and Congress, with new emphasis on green energy, carbon taxes, anti-fracking legislation, elimination of subsidies to oil and gas companies, rejection of new pipelines, and so on. Climate prophet Bill McKibben is in the midst of a 21-city "Do the math" tour, drawing thousands of supporters, all demanding that carbon dioxide be left in the ground. Fossil fuels are choking the planet, and a critical mass of Americans are waking up to it.

American denial of climate change hit bottom this month. Hurricane Sandy was the most powerful instance yet of mundane weather trumping abstract science to make people face the truth. “It’s Global Warming, Stupid!” screeched the cover of Bloomberg Businessweek, above a photo of a flooded street. Rising sea levels just moved from future threat to present danger. And as the Pentagon had earlier this year emphasized climate change as a national security issue, so the CIA has just released its own grim assessment of coming “climate surprises” with “global security implications serious enough to compel international response.” In his post-election acceptance speech, President Obama warned of “the destructive power of a warming planet.”

Geoengineering refers to manipulations of the structures of the natural world aimed at protecting the livable environment. Interventions can go further than, say, massive storm surge barriers protecting Amsterdam and London, or levee systems keeping New Orleans dry. Greenhouse gases can actually be removed from the atmosphere, and solar radiation can be managed in ways that reduce the planet's absorption of heat. Stratospheric dispersal of sulfur aerosols to mimic the light-dimming consequences of volcanic ash is one geoengineering scheme. Another involves iron fertilization of the oceans to produce massive plankton blooms, which can repair broken aquatic food-chain webs, while lowering carbon dioxide levels.


Weather manipulation has been around since cloud-seeding for rain, but these more drastic strategies are hugely controversial. Last July, a freelance geoengineer — some called him rogue — dumped 100 tons of iron sulphate into the Canadian Pacific, the largest deliberate ocean fertilization ever. A plankton bloom covering thousands of square miles of ocean resulted. The action was defended as a restoration of nutrients that would bring back the salmon stock in the region, and it was intended to create a carbon sink as well, but many scientists decried the iron-dump as a careless violation of international agreements. Now the actual consequences of the Pacific undertaking are being studied.


Some argue that, given the already permanent and growing character of the greenhouse threat, such drastic manipulations of atmospheric systems are urgently needed — if carried out in scientifically responsible ways. But others warn that geoengineering techniques can make things far worse. Opposition movements rally with slogans like "Hands off Mother Earth." Meanwhile, a subtler worry is that widespread talk about engineered solutions to climate change will lessen curbing pressures on Big Oil and other fossil fuel producers. And what about the possibility of a climate war between nations of the chilly north and the overheated south, with engineered planet temperatures wielded as a weapon?

Once again, we humans find ourselves at a moral threshold, where technology poses unprecedented challenges to our capacity for ethical choice. Biomedical engineering, artificial intelligence, nanotechnology, genetic modification of agriculture, cellular manipulation for reproductive "enhancement": These frontiers of science are also boundaries of wisdom. What is the right thing to do?


In the case of the environment, though, the pressures come not from newfound capabilities, but from a doomsday clock that we ourselves set ticking. Having only now approached a broad popular consensus that climate change is a problem, we must promptly imagine far more expansive solutions. Reducing fossil fuels is urgently necessary, but probably insufficient. Let sensible discussion of creative interventions begin. For Mother Earth, and all her children.

James Carroll's column appears regularly in the Globe.