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Kristin Eberhard’s Blog

Clinging to linearity in an exponential world

Kristin Eberhard

Posted July 17, 2012

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North Carolina made news last month by legislatively nullifying climate change. As ridiculous as this seems, the mindset underlying North Carolina’s action is all too common. And I don’t mean the mindset of denying climate change; I mean the mindset of assuming things will continue in the future largely the same as they have in the past.

You need look no further than real estate advice to see that this mindset is rampant and can be destructive when it is wrong (as it often is).

The question that faced North Carolina is one many of us face all the time: We know how things have gone in the past; so what do we know about how they will go in the future?












Sometimes, we are tempted to think that things will always be exactly like they are at the present moment.  That the future extends out in a flat line.  Coffee will always cost 10 cents.  Gas will always cost $3/gallon.  Middle class families will always be able to send their kids to college.

Hopefully you recognize this is almost never true.

The more common conception is that current trends will continue.  Things will change, but at the same rate that they have changed in the past.  This is the tack that North Carolina took when it declared that state agencies had to use historical data and linear extrapolation, not the exponential predictions coming from most recent scientific studies, when predicting future sea water levels. The price of a cup of coffee will continue rising at a slow but steady rate.  College costs will continue to rise at the same rate as they have in the past. This approach usually seems logical, reasonable, and defensible because it is simply an extension of historical data - drawing the same line out into the future.












Unfortunately, despite the veneer of being reasonable and data-driven, this assumption is often wrong.  Despite our instinct to see linear trends, many trends are actually exponential.  This means the rate of change is changing. Things are not just changing, they are changing faster and faster. Data and models will reveal a path that looks more like this:

It is not just models that show exponential trends; we have many historical examples, particularly relating to human activities in the past 200 years.  And these are often wonderful things, like there being more people, who have increasingly powerful tools at their disposal.

The fact that, in just a few hundred years, we have advanced from being limited to making predictions based on observations made during our own lifetime, or perhaps the lifetimes of just a few generations, to now being able to predict that sea levels are going to change in a way that we've never actually observed, is nothing short of amazing. However, we have to embrace the tools we have developed and use them.

Here is the sea level rise that scientists predict for North Carolina (exponential):

And here is the official prediction they legislatively adopted (linear):

We must allow ourselves to do what we do best as humans - invent and utilize tools to augment our natural abilities. Sometimes things change quickly and unexpectedly, but we are uniquely equipped to predict those changes and deal with them, if we let ourselves. Denying our hard-earned knowledge is like tying our hands behind our back as we are about to enter the ring for the fight of our lives.  Let’s untie our hands, look the changing future square in the face, and fight.

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Switchboard is the staff blog of the Natural Resources Defense Council, the nation’s most effective environmental group. For more about our work, including in-depth policy documents, action alerts and ways you can contribute, visit

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