An Introduction

By Josh Howe, Associate Professor of History and Environmental Science, Reed College

In Oregon, within a few hundred miles you can see snowy volcanoes, parched deserts, semiarid grasslands, alpine meadows, and coastal temperate rain forests. On any given day, the weather across the state can range from freezing cold to baking hot, from bone dry to soaking wet, from tranquil to tempestuous. Oregon regularly experiences the extremes of average precipitation, temperature, humidity, and wind characteristic of the North American West. Some places in the Coast Range, for example, receive as many as 200 inches of rain in some years, while the rain shadow of Steens Mountain in eastern Oregon sometimes receives as little as five inches. But even highly variable weather creates patterns over time, and scientists use the word climate to describe those patterns over decades, or even centuries.

Oregon’s climate is not only diverse, it is also changing. In geological time—the intervals of time that geologists use to chart changes and sequences of events in the rock record—Oregon’s climate has vacillated between tropical and arctic. Since the Industrial Revolution, however, human activity has contributed to changes in the Earth’s climate, causing geological change on shorter, human timescales. Scientists refer to the changes that humans make to climate as anthropogenic Climate Change, which have occurred largely as a result of changes in the composition of the atmosphere, particularly through the emission of greenhouse gases like CO2 that increase the overall temperature of the Earth. Because anthropogenic climate change, on balance, increases the overall temperature of the planet, it is also often referred to as anthropogenic warming or, more commonly, global warming. The terms are not perfectly interchangeable, but both have been used to describe the causes of the climate crisis, a term scientists and concerned citizens often use to refer to the related negative effects of an increase in average global temperatures on animal and human populations, as well as the ecosystems and infrastructure on which they rely.

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Keeling Curve

The Keeling Curve is a graphic representation of the concentration of CO2 (carbon dioxide) in the atmosphere. In 1958, climate scientist Charles Keeling, who worked at the California Institute of Technology, began testing air samples for CO2 at the Mauna Loa Observatory in Hawaii and in Antarctica. He recorded changes in CO2 concentrations throughout the day, from month to month and year to year. Plotting the data on a graph, he demonstrated the correlation between rising CO2, which contributes to a warming planet, and an increase in the use of fossil fuels by humans. Scientists continued adding new data to the graph along a continuous timeline, making the Keeling Curve a valuable tool for recording—and visually understanding—how the history of human activity, the rise of CO2, and climate change are connected.

"The Keeling Curve, the oscillating upward-sloping graph of measured atmospheric carbon dioxide (CO2)," environmental historian Joshua Howe wrote, is "one of the most important and powerful scientific symbols of anthropogenic [human-caused] climate change. It may seem odd to read a simple measure of atmospheric gas through the many-sided prism of modern American life the way you might read a historical photograph or piece of art. And yet the Keeling Curve functions as much as a symbol in our collective understanding of climate change as it does a representation of data about CO2." [Howe, "This is Nature; This is Un-Nature: Reading the Keeling Curve," Environmental History 20 (2015): 286-93.]