Nature stopped being natural decades ago.
That is to say, starting the mid-19th century, human activity has changed global ecosystem conditions in ways that fall outside the normal variations visible in geological records. This hasn't been through malice, but through ignorance. We're only now beginning to get a grip on the enormous complexity of geophysical systems. But as we learn more about how the global environment works, one thing has become increasingly clear: we're heading rapidly towards a planetary catastrophe.
Frustratingly for those of us who follow this matter closely, we've known for awhile what needs to be done in order to avoid such disaster: eliminate fossil fuel-based energy production as rapidly as humanly possible, globally; reduce agricultural practices (including the raising of cattle) that add disproportionate levels of greenhouse gases; and make changes to the structure of the global economy, urban systems, food Webs, transportation networks, and energy grids to enable such changes to improve our overall quality of life. A daunting task, to say the least, but well within the capacities of our current technological and economic know-how.
This situation is frustrating because there are few signs that global institutions are ready to undertake this scale of change--and plenty of signs of delay. American readers may be acutely aware of the sluggish pace of change here, but resistance to making necessary alterations of social, technological, and economic systems can be found from Beijing to Berlin. If the most heated claims of climate scientists are true, such delays might one day be considered to have been criminal.
But if shouting louder (and maybe stamping our feet for emphasis) won't make global political and economic leaders act swiftly, what are our options?
We could try to adapt to global warming as we continue to make slow reductions in carbon emissions, knowing that effects like drought, famine, opportunistic pandemic disease, global refugees, resource conflict, and more will still hit us, killing many tens of thousands--perhaps even tens of millions. As such disasters hit, we'll start acting faster; hopefully, the cascading impacts of climate disruption won't become barriers to making the kinds of changes we need.
We could cross our fingers and hope that new "magic bullet" technologies will make a change to a carbon-free economy easy and cheap, and perhaps even remove excess carbon from the atmosphere. It's certainly possible, especially with the potential development of molecular manufacturing. But counting on such developments emerging exactly as we hope, as rapidly as we wish, seems a bit like counting on winning the lottery--it would be lovely if it happened, but it's hardly the basis of sound financial planning.
And both adaptation and magic technologies suffer from the "climate lag" problem. In short, the global climate is a slow system, and doesn't change quickly. Today's warming is the result of greenhouse gas emissions in the 1960s and 1970s, and present-day emissions will continue to warm us for decades to come, even if we stopped emitting any greenhouse gases tomorrow. The longer we wait to act, whether out of political inertia or dreams of magical technologies, the worse the situation will be for at least a generation.
There is another option, one that holds its own set of risks. Geoengineering is the intentional manipulation of global ecosystem patterns in order to trigger a particular change to the environment and climate. Some of the geoengineering proposals are outlandish and expensive, but many are relatively straightforward--if anything operating on a global scale, and likely requiring decades to undertake, could be called straightforward. Geoengineering would be used to slow the rate of global warming-induced climate disruption, allowing us to make the necessary changes to our economies and infrastructure before disaster hits.
To say this proposal is controversial would be a vast understatement. A growing debate includes governments, NGOs, and scientists from all over the world as both advocates and opponents. If geoengineering works, it would suppress global warming and give us the time needed to eliminate carbon emissions. But it's also wildly risky, certain to provoke international tension, and brimming with the potential for unintended consequences.
Most of the debates around geoengineering focus on efforts to directly manage temperatures, particularly through the use of stratospheric injection of sulfates modeled on the effects of massive volcanic eruptions. Global temperatures dropped by half-a-degree Celsius in the months after the 1991 Mt. Pinatubo eruption; a sustained project to introduce sulfates into the stratosphere could keep temperatures down. We even have a decent idea of what kinds of immediate problems this would cause, including damage to the ozone layer and a measurable reduction of solar power efficiency.
However, there is also the potential for as-yet unknown consequences. Some models show sulfate injection altering rainfall patterns, for example, potentially inducing droughts and triggering storms in places that wouldn't necessarily have been hit in a no-geoengineering scenario. It's also entirely possible that we simply still don't know enough about Earth's complex geophysical systems to "engineer" them, and that any attempt to manipulate the climate in this way might cause problems even greater than those coming from global warming.
But the biggest questions about geoengineering aren't technical, they're political. Geoengineering would be global in impact. So who determines whether or not it's used, which technologies to deploy, and what the target temperatures will be? Who decides which unexpected side-effects are bad enough to warrant ending the process? What happens if a nation that claims to see a benefit from warmer temperatures, like Russia already has, demands that geoengineering not go forward, or be sharply limited? And given that the cost of many geoengineering projects would be low enough for a single country to undertake, what happens when a desperate "rogue nation" attempts geoengineering against the wishes of other states?
Ultimately, desperation is a powerful driver. If we start to see faster-than-expected increases in temperature, deadly heat waves and storms, crop failures and drought, the pressure to do something, anything, will be enormous. In such a scenario, we will face a choice between near-certain disaster and unknowable complexity. Let's hope our civilization is up to the challenge.