For almost 20 years, I’ve been spending time on a craggy stretch of British Columbia’s shoreline called the Sunshine Coast. This summer, I had an experience that reminded me why I love this place, and why I chose to have a child in this sparsely populated part of the world.

It was 5 a.m. and my husband and I were up with our 3-week-old son. Looking out at the ocean, we spotted two towering, black dorsal fins: orcas, or killer whales. Then two more. We had never seen an orca on the coast, and never heard of their coming so close to shore. In our sleep-deprived state, it felt like a miracle, as if the baby had wakened us to make sure we didn’t miss this rare visit.

The possibility that the sighting may have resulted from something less serendipitous did not occur to me until two weeks ago, when I read reports of a bizarre ocean experiment off the islands of Haida Gwaii, several hundred miles from where we spotted the orcas swimming.

There, an American entrepreneur named Russ George dumped 120 tons of iron dust off the hull of a rented fishing boat; the plan was to create an algae bloom that would sequester carbon and thereby combat climate change.

Mr. George is one of a growing number of would-be geoengineers who advocate high-risk, large-scale technical interventions that would fundamentally change the oceans and skies in order to reduce the effects of global warming. In addition to Mr. George’s scheme to fertilize the ocean with iron, other geoengineering strategies under consideration include pumping sulfate aerosols into the upper atmosphere to imitate the cooling effects of a major volcanic eruption and “brightening” clouds so they reflect more of the sun’s rays back to space.

The risks are huge. Ocean fertilization could trigger dead zones and toxic tides. And multiple simulations have predicted that mimicking the effects of a volcano would interfere with monsoons in Asia and Africa, potentially threatening water and food security for billions of people.

So far, these proposals have mostly served as fodder for computer models and scientific papers. But with Mr. George’s ocean adventure, geoengineering has decisively escaped the laboratory. If Mr. George’s account of the mission is to be believed, his actions created an algae bloom in an area half of the size of Massachusetts that attracted a huge array of aquatic life, including whales that could be “counted by the score.”

When I read about the whales, I began to wonder: could it be that the orcas I saw were on their way to the all-you-can-eat seafood buffet that had descended on Mr. George’s bloom? The possibility, unlikely though it is, provides a glimpse into one of the disturbing repercussions of geoengineering: once we start deliberately interfering with the earth’s climate systems — whether by dimming the sun or fertilizing the seas — all natural events can begin to take on an unnatural tinge. An absence that might have seemed a cyclical change in migration patterns or a presence that felt like a miraculous gift suddenly feels sinister, as if all of nature were being manipulated behind the scenes.

Most news reports characterize Mr. George as a “rogue” geoengineer. But what concerns me, after researching the subject for two years for a forthcoming book on climate change, is that far more serious scientists, backed by far deeper pockets, appear poised to actively tamper with the complex and unpredictable natural systems that sustain life on earth — with huge potential for unintended consequences.

In 2010, the chairman of the House Committee on Science and Technology recommended more research into geoengineering; the British government has begun to spend public money in the field.

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Bill Gates has funneled millions of dollars into geoengineering research. And he has invested in a company, Intellectual Ventures, that is developing at least two geoengineering tools: the “StratoShield,” a 19-mile-long hose suspended by helium balloons that would spew sun-blocking sulfur dioxide particles into the sky and a tool that can supposedly blunt the force of hurricanes.

THE appeal is easy to understand. Geoengineering offers the tantalizing promise of a climate change fix that would allow us to continue our resource-exhausting way of life, indefinitely. And then there is the fear. Every week seems to bring more terrifying climate news, from reports of ice sheets melting ahead of schedule to oceans acidifying far faster than expected. At the same time, climate change has fallen so far off the political agenda that it wasn’t mentioned once during any of the three debates between the presidential candidates. Is it any wonder that many are pinning their hopes on a break-the-glass-in-case-of-emergency option that scientists have been cooking up in their labs?

But with rogue geoengineers on the loose, it is a good time to pause and ask, collectively, whether we want to go down the geoengineering road. Because the truth is that geoengineering is itself a rogue proposition. By definition, technologies that tamper with ocean and atmospheric chemistry affect everyone. Yet it is impossible to get anything like unanimous consent for these interventions. Nor could any such consent possibly be informed since we don’t — and can’t — know the full risks involved until these planet-altering technologies are actually deployed.

While the United Nations’ climate negotiations proceed from the premise that countries must agree to a joint response to an inherently communal problem, geoengineering raises a very different prospect. For well under a billion dollars, a “coalition of the willing,” a single country or even a wealthy individual could decide to take the climate into its own hands. Jim Thomas of the ETC Group, an environmental watchdog group, puts the problem like this: “Geoengineering says, ‘we’ll just do it, and you’ll live with the effects.’ ”

The scariest thing about this proposition is that models suggest that many of the people who could well be most harmed by these technologies are already disproportionately vulnerable to the impacts of climate change. Imagine this: North America decides to send sulfur into the stratosphere to reduce the intensity of the sun, in the hopes of saving its corn crops — despite the real possibility of triggering droughts in Asia and Africa. In short, geoengineering would give us (or some of us) the power to exile huge swaths of humanity to sacrifice zones with a virtual flip of the switch.

The geopolitical ramifications are chilling. Climate change is already making it hard to know whether events previously understood as “acts of God” (a freak heat wave in March or a Frankenstorm on Halloween) still belong in that category. But if we start tinkering with the earth’s thermostat — deliberately turning our oceans murky green to soak up carbon and bleaching the skies hazy white to deflect the sun — we take our influence to a new level. A drought in India will come to be seen — accurately or not — as a result of a conscious decision by engineers on the other side of the planet. What was once bad luck could come to be seen as a malevolent plot or an imperialist attack.

There will be other visceral, life-changing consequences. A study published this spring in Geophysical Research Letters found that if we inject sulfur aerosols into the stratosphere in order to dial down the sun, the sky would not only become whiter and significantly brighter, but we would also be treated to more intense, “volcanic” sunsets. But what kind of relationships can we expect to have with those hyper-real skies? Would they fill us with awe — or with vague unease? Would we feel the same when beautiful wild creatures cross our paths unexpectedly, as happened to my family this summer? In a popular book on climate change, Bill McKibben warned that we face “The End of Nature.” In the age of geoengineering, we might find ourselves confronting the end of miracles, too.

Mr. George and his ocean-altering experiment provides an opportunity for public debate about an issue essentially absent during the election cycle: What are the real solutions to climate change? Wouldn’t it be better to change our behavior — to reduce our use of fossil fuels — before we begin fiddling with the planet’s basic life-support systems?

Unless we change course, we can expect to hear many more reports about sun-shielders and ocean fiddlers like Mr. George, whose iron dumping exploit did more than test a thesis about ocean fertilization: it also tested the waters for future geoengineering experiments. And judging by the muted response so far, the results of Mr. George’s test are clear: geoengineers proceed, caution be damned.