In my first post on this topic, I explored how optimism and pessimism can influence policy preferences for dealing with climate change. I mentioned two key issues relating to policy choices: 1) society’s sensitivity to earth system disturbance, and 2) our potential to mitigate. Each can be viewed with optimism or pessimism, which leads to four possible perspectives: the true optimists, true pessimists, earth system optimists (who are mitigation pessimists), and mitigation optimists (who are earth system pessimists).
Today I’ll focus on the evidence that can support or diminish the standing of each of the four perspectives.
Society’s resilience to the earth system disturbances like that caused by human emissions of greenhouse gases will depend on two factors: 1) the size of the disturbance, and 2) our ability to cope with the resulting impacts.
Size of the disturbance
Evidence relating to the size of the disturbance that will result from our emissions is largely scientific. We know a great deal.
We know that human activities have changed the composition of the atmosphere (e.g., CO2 concentrations have increased by ~35%, methane increased by ~150%, and nitrous oxide increased by ~18%). We know that climate is changing based on multiple independent lines of evidence. Human responsibility for the recent changes in climate is also well established (see IPCC AR4 WG I for more).
We also know that the seemingly small changes in globally averaged temperature that occurred prior to the onset of human civilization translated into large changes in the earth system. For example, temperatures 4-5ºC cooler caused ice sheets a mile high to cover parts of the northern United States and led to sea levels 120 meters (~400 feet) lower than today. Temperatures 1-2ºC warmer led to sea levels that were 4-6 meters (13-20 feet) higher than today. Although sea level changes like this may unfold slowly they illustrate unambiguously that small changes in temperature translate into big changes in the earth system.
With an additional 1-2ºC warming, we also expect to see substantial changes in extreme weather events, increasing stress on biological systems including putting 20-30% of species at risk of extinction, drying of semi-arid regions, losses of alpine snow pack, and melting arctic sea ice, among a range of other impacts (see IPCC WG II, ch. 19 for more). These are what I would call basic changes in the characteristics and functioning of the earth system. In most cases initial changes are already visible.
These impacts suggest that our greenhouse gas emissions constitute a large disturbance in the earth system—support for a pessimistic view.
Human ability to deal with earth system disturbance
In many respects, human civilization has done remarkably well, often in the face of adversity and long odds. For example, we’ve made impressive advances in agriculture, technological innovation, medical care, and scientific understanding.
But we haven’t accomplished much when it comes to coping with climate changes. Human civilization has existed during a relatively stable period in earth’s climate—global changes in temperature have been minimal over the last 10 thousand years. We simply haven’t gone through anything like what we might see this century.
Furthermore, we’ve adapted ourselves to the current climate conditions. This loads the dice against beneficial changes and towards harmful impacts. Even more importantly, many of the physical and natural systems that we depend upon are heavily adapted to current climate conditions. Therefore, even if we can respond quickly we’re limited by the speed that physical and natural systems respond. We’re also looking at faster rates of climate change over the next century than what appears to have occurred over the last several hundred thousand years. That means that we, and the physical and natural systems that we depend upon, won’t have much time to respond.
Generally, this suggests that society is sensitive to earth system disturbance—further support for pessimism on this issue. (NB: if you see it differently please share your views, as they could add greatly to this discussion).
How about our ability to reduce emissions and thrive?
Here I see stronger reasons for optimism. Past efforts to deal with societal problems (environmental and otherwise) have often been easier than we imagine at the outset—especially, I might add, relative to gloomy predictions made by pessimists.
Past environmental successes include phasing out chemicals that deplete stratospheric ozone, reducing emissions of traditional air pollutants, cleaning up water pollution, and bringing at least some species back from the brink of extinction. We’ve also been highly successful in overcoming other societal challenges and making technological advances like adding seat belts and air bags to cars, mobilizing the U.S. for World War II, developing a space program, and creating powerful weapon systems. All speak to an impressive human capacity for innovation that would seem to apply well to the challenge of transforming to a cleaner economy.
Nevertheless, political obstacles to reducing emissions remain substantial. These stem from a range of factors including long time horizons, special interest opposition, potentially serious distributional consequences, the complexity of the underlying science (particularly when combined with widespread scientific illiteracy among policy makers, members of the media, and the public), and uncertainty over policy implications.
Together this implies that we have great capacity to mitigate and thrive but that political obstacles and weak leadership must be overcome for this potential to be realized. Evidence, perhaps, for both optimism and pessimism.
Nevertheless, I’m optimistic about overcoming political obstacles because I have faith that the best politics comes from crafting good policy and believe that policies grounded in our best available knowledge have the best chance of benefiting society (as I recently said here). As a result, I’m optimistic about society’s mitigation potential.
One final thought on the earth system optimists who are mitigation pessimists. I find it hard to see a way to support this view.
The reason is that dealing with earth system disturbance involves overcoming challenges arising simultaneously in physical, natural, and social systems—mostly outside of our directly control. Furthermore, the complexity of the earth system means that some impacts will be hard to anticipate and some surprises are likely. In contrast, the challenge of reducing greenhouse gas emissions involves altering human activities alone—a far more straightforward challenge and entirely within our control.
It makes very little sense to believe that humans are clever and capable enough to overcome the complex challenge posed by earth system disturbance while simultaneously believing that we aren’t capable of reducing emissions. That doesn’t add up.