Climate Change: The Real Deal

Nat Keohane


The Economist had an interesting piece on climate science this week which is attracting some attention. The article reaffirmed, yet again, that greenhouse gases are changing our climate in dangerous ways. But it also pointed to a scientific puzzle: that warming may not have advanced in the last decade as much as current models predicted, given the amount of emissions the world has produced. 

My main take-away is that the article underscores the fundamental nature of climate change — that we are creating dangerous uncertainties.  (As you can imagine, some of the usual suspects are using questions about the details of climate science to deny climate change entirely. Never mind that the Economist article is quite clear that the issues raised in no way alter the fact that greenhouse gas pollution is disrupting our climate.)

In fact, no one knows for sure how much damage we are doing through our large-scale changes to the natural world. To my mind, that uncertainty is a powerful reason for taking remedial action now  – not only because there are a range of actions that will pay off under virtually any probable scenario, but also because action now keeps open the option to do more later if the science warrants it.

We know there are dangerous climate disruptions coming. So, regardless of how quickly it gets hotter, we need to stop making investment decisions that make things worse, like building power plants that produce a lot of pollution. We need to base our decisions on the big scientific picture, which shows that climate is being changed by pollution, and not the evolving predictions of how much and how fast this is happening.

Of course, if the climate is warming a little more slowly than we thought, that would be great news.  Given that we haven’t yet implemented a comprehensive strategy to combat warming, slower warming would buy us time. But at best that’s a little like hearing “the earthquake that’s coming may only be a 6.7, not a 7.3” or “the disease may spread through the population a little more slowly than we thought.”

We need to be open to the possibility that the Economist is right.  Honest scientific inquiry should never rule out new ideas.  The experts at Climate Nexus, though, point to a few potential problems with the science in the piece.  They note that a growing number of studies have documented heat being redirected into the ocean instead of the atmosphere; and that the selection of a 15-year timeframe incorrectly compares current atmospheric temperatures with those of an anomalously warm El Niño period. They also raise the issue of ongoing research into aerosols (fine particulate matter in the atmosphere), which show it may be obscuring atmospheric warming we would otherwise see.

Being an academic by training, I can’t help but add a few questions of my own. First, the article and the studies it draws on may be making too much out of what is a short and recent trend.  Using just the last ten years of climate data is probably misleading, since it is dominated by a few relatively cool years.  It still seems hard to believe that we can infer a lot about long-term equilibrium climate sensitivity from a handful of data points.  The longer-term trends are quite clear.

 Second, some of what is going on appears to be disagreement among different types of climate models.  A careful reading of the piece reveals that the low-end estimates of climate sensitivity are coming from one particular type of model (top-down or “energy balance” models), which are highly simplified and potentially influenced too much by recent data. The more complex bottom-up models tend to suggest higher sensitivities – that is, more warming. 

Third, as the article itself points out, the link between concentration and temperature rise is only part of the story.  Relative to projections of just a few years ago, emissions are increasing faster than expected in most of the world (even if they may be leveling off in the United States).  On the current trajectory, even if the climate sensitivity is “only” 2 degrees, we will still have more than 2 degrees of warming – getting well into the region where science suggests we will start to see significant adverse impacts on the climate system.  

Given that we are already seeing severe impacts (increased incidence of drought, extreme weather, etc.) linked to the warming observed so far, the effect of even modest temperature increases could be worse than we thought.  Indeed, even if the studies about climate sensitivity are correct, the implications for policy are not so clear-cut.  As the Economist article points out, actual policies lag well behind what we think is needed.  Even with a lower climate sensitivity, we would need to step up our policies – for example, by putting a price on carbon pollution, as the last paragraph of the article suggests we must do.

The article raises an interesting scientific question, which is always good.  But it is worrisome that some people are already ignoring the nuances of the piece and misusing it to confuse the public. The real message, as the article says, is that even if they’re right, it “does not mean the problem is going away.” I hope people take the time to read and digest the whole piece; it would be too bad if most readers walked away thinking that this means we don’t need to do anything about climate change.

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