Air-Conditioning Needs and Cartographic Failure at the Washington Post

The Washington Post recently ran an article entitled “Addicted to Cool: How the Dream of Air Conditioning Turned into the Dark Future of Climate Change,” which features three maps of “Summer Days Requiring AC” in the U.S. at different periods of time (1981-200, 2001-2002, and 2060). As expected, the region needing air conditioning is projected to expand. Determining how many days actually “require” air conditioning is, however, an impossible task, as different people vary significantly in their cooling desires and demands, while housing design and shade considerations make big differences as well. Understandably bypassing such complexities, the newspaper used the heat index, a measurement of temperature and humidity, as a proxy. Unsurprisingly, their maps show that a large area of the country already needs summer air conditioning, and that in the decades to come the need for cooling will geographically expand.

The maps included in the article, however, are not impressive, to put it mildly. Their problems are particularly severe regarding California. As can be seen on the map detail of Southern California posted below, the Post’s mapping accurately shows the eastern deserts and the inland western regions as needing air conditioning on most if not all summer days. It also accurately depicts the highest elevation areas as rarely requiring it. But the same map also portrays the coastal zone as AC-dependent. This is not true. Downtown San Diego, for example, has an average July high temperature of 75 degrees Fahrenheit and an average July low of 66 (over the 1991-2020 period). Further north, in Rancho Palos Verdes, similar conditions prevail. According to Weather Spark, “The hottest month of the year in Rancho Palos Verdes is August, with an average high of 76°F and low of 64°F.” The same site also notes that “Over the course of the year, the temperature typically varies from 51°F to 76°F and is rarely below 46°F or above 84°F.” This is climate that very rarely calls for cooling.

The map is equally inaccurate in its depiction of Northern California. As can be seen on the map detail posted below, it does capture the cool summers characteristic of the coastal regions in and around San Francisco and Monterey bays. It completely misses the fact, however, that other coastal regions also have mild summers. The average July high and low temperatures in Point Arena, Santa Cruz, and Carmel are, respectively 65 and 50 degrees F.; 74 and 54; and 70 and 53 (all based on the climatological data found in the Wikipedia articles on these towns). In Point Arena, one is more likely to want heating than air conditioning in June and July, yet the map indicates that cooling is needed on most summer days.

Other odd features mar the map. As can be seen, the city of San Francisco is mislocated in the bay and on its eastern shore.  The national map also features a faint white line that traces part of San Francisco Bay and would appear to indicate the actual coastline, at least in some areas.  Was one map imprecisely overlaid on another?

Although these problems are serious enough, it is the map of projected air-conditioning needs in the year 2060 that truly fails. This can be seen easily on the paired maps showing current and projected AC requirements in California. Here much of the currently cool Big Sur coastal zone is projected to have much reduced air-conditioning needs by 2060. This region of projected cooling is bizarrely shown as extending over the Santa Lucia Range into the southern Salinas Valley, an area that now experiences warm summers (King City has an average July high of 85 degrees F.). Similarly, the currently warm inland area north of Santa Barbara is shown as being expected to have much cooler summers in 2060 than it does today, while with the rest of Southern California is projected to warm.

One can only wonder whether the cartographers in question actually examined these maps before publication, or, if they did, whether they have much of an understanding of the geography of climate. It often seems that journalists use maps as mere ornaments or, alternatively, to have the appearance of spatial precision without the substance. The maps in this article do little more than make the trite point that “more of us will need air conditioning as the climate warms.” Readers deserve better, especially from a once-great paper that is owned by the third richest person in the world.

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