Outsourcing our thermoregulation to the city

The cold in Yakutsk, Russia. Courtesy of http://www.snowaddiction.org

In the middle of winter in Yakutsk, Russia, the average temperature is -34 °C–so cold that the difference between Celsius and Fahrenheit is negligible.  Overnight dips to -42 °C are common.  For the 270,000 people who live there, time outside is to be avoided—eyeglasses freeze to your face, eyelashes freeze, your nose hairs freeze.  October to April is spent scurrying around from house to house and spending as much time as possible inside.

In July in Kuwait City, Kuwait, the 2.4 million residents endure average highs of 47 °C (116 °F) in the blistering heat of the day.  Overnight offers a small amount of relief, at 31 °C (87 °F).  Recently a remote area in the northwest of the country hit a blistering 54 °C (129 °F), which may have a planet-wide record.  Citizens again stay inside as much as possible, sheltering in the refreshing air conditioning.

The relationship between heat production (metabolic costs) and air temperature is called a Scholander-Irving curve, and is generally “U-shaped”, with increases both above and below the thermoneutral zone. Here we show this relationship for a variety of mammals, with every mammal having a slightly different thermoneutral zone as well as a different slope describing the increased costs at changing temperatures. From Hill et al. 2013, PLoS ONE.

These two cities, opposite in their climate, have one thing in common.  Their human residents, as descendants of tropical mammals, cannot handle temperature extremes; in fact, humans are one of the mammals that are least able to withstand temperature variation. As part of their unparalleled success in colonizing the corners of the planet, humans have extended their regulation of body temperature from just their own bodies to the scale of the city. What I’d like to discuss, however, are the accompanying energetic costs.

Generally, mammals such as humans must maintain a relatively constant body temperature in the face of changing external conditions for their physiological functions to continue. This process is called thermoregulation.  When their external environment is too cool, mammals expend energy in shivering and other processes to maintain that constant body temperature.  When their external environment is too hot, mammals shed heat by sweating, redirecting blood flow, and other physiological processes.  The relationship between ambient temperature and a mammal’s metabolic rate is therefore a “U” shape (called a Scholander-Irving curve after its discoverers, Scholander et al., 1950). The range of temperatures in which no additional energy use is needed for thermoregulation is called the “thermoneutral zone”.  This zone is particularly narrow in humans.

Humans also have a relationship between energetic costs and ambient temperature. A) This shows the very steep increased cost with decreasing temperature, as well as relatively narrow thermoneutral zone (higher temperatures were not tested). B) How changing insulation changes the shape of the Scholander-Irving curve. C) Houses increase energy usage at low temperatures. D) This can be scaled to the size of a city. From Hill et al. 2013, PLoS ONE.

By building cities, humans have “outsourced” the cost of thermoregulation.  Now, instead of expending biological energy to maintain optimal body temperature, we expend fuel.  Globally, heating and cooling buildings is responsible for 40% of total energy use and 33% of greenhouse gas emissions (UNEP, 2009). And in fact, if you measure the change in energy consumption in cities over a range of temperatures, you get what looks suspiciously like the Scholander-Irving curve writ large: a city-wide relationship between energy use and ambient temperature (Hill et al., 2013).  But this expansion of thermoregulated area doesn’t come cheap—a recent estimate places the increased cost of maintaining an entire house at a comfortable temperature at 50 times the cost of maintaining body temperature for just the people in it (Meehan, 2012).

This outsourcing of thermoregulation has other interesting consequences.  A recent study confirmed what many women in the workplace have long suspected—that the air conditioning is set too low.  In fact, air conditioning is set for the thermoneutral zone of a 40 year old man, while women generally have higher thermoneutral zones (Kingma and van Marken Lichtenbelt, 2015).  Setting air conditioning to allow higher temperatures may reduce overall energy demand of the city.

The number of days each year that exceed limits in which heat can be deadly for humans. a) The average number of lethal heat days between 1995 and 2005. b) – d) Projected average days in 2100 under differing climate change scenarios. b) Scenario RCP 2.6 represents rapid and immediate decline in greenhouse gas emissions, c) Scenario RCP 4.5 represents a later decline in greenhouse gas emissions and d) Scenario RCP 8.5 represents a “business as usual” model where emissions are not reduced. Figure from Mora et al. 2017 Nat. Clim. Change.

Given these relationships, the change in global energy demand (and burning of fossil fuels) that may have occurred due to the Anthropocene is hard to quantify, since it depends on how much time different cities around the world spend in their own thermoneutral zones.  But with increased warming, more time spent above the thermoneutral zone, particularly in tropical cities, may end up rapidly increasing the amount of energy we spend in our extended phenotype of the thermoregulated city.  In fact, the large Asian cities of Hong Kong, Seoul, and Tokyo have increased their thermoregulatory energy demand by ~10% over the past 20 years, and this is projected to increase with climate warming (Spandagos and Ng, 2017).

But sometimes the amount of thermoregulation we can create in our city isn’t enough.  In 2003, an unusual heat wave hit Europe that broke records set in 1540, killing at least 70,000 people.  In fact, over the past 34 years, 164 cities across the globe have experienced heat waves that have led to the deaths of hundreds of thousands of people (Mora et al., 2017).  A total of 30% of the world’s population is currently at risk of such extreme heat events, and projected climate change suggests this will increase to over two thirds of the human population. (See this interactive map of lethal heat days.) And as temperatures warm, increased demand on city-wide energy grids will make brown-outs much more likely.

The probability of these lethal heat events is also increasing directly because of urbanization.  Because of the energetic costs of thermoregulation, as well as the heat absorption by paved surfaces, cities themselves directly cause warming in the well-documented “heat island effect“.  These effects are most pronounced in the heat of the day, adding as much as 12° C in temperature and exacerbating the probability of lethal heat and the costs of cooling.

The heat island effect in cities changes as a function of the type of surface. Figure courtesy of the EPA.

What does this mean for cities in the Anthropocene?  Our fragility and tropical evolutionary heritage means we cannot ignore the costs of thermoregulation.  Increasing passive cooling techniques like windows, improved glazing, and more park areas can significantly reduce city temperatures and therefore energy use, even in places as warm as the UAE (Taleb, 2014).  How we choose to build our cities will significantly change the risk of lethal heat and the risks of increased warming due to energy demand.

Hill, R. W., Muhich, T. E. and Humphries, M. M. (2013). City-Scale Expansion of Human Thermoregulatory Costs. PLoS One 8, e76238.
Kingma, B. and van Marken Lichtenbelt, W. (2015). Energy consumption in buildings and female thermal demand. Nat. Clim. Chang. 5, 1054–1056.
Meehan, T. D. (2012). Energetics of thermoregulation by an industrious endotherm. Am. J. Hum. Biol. 24, 713–715.
Mora, C., Dousset, B., Caldwell, I. R., Powell, F. E., Geronimo, R. C., Bielecki, C. R., Counsell, C. W. W., Dietrich, B. S., Johnston, E. T., Louis, L. V., et al. (2017). Global risk of deadly heat. Nat. Clim. Change. 7, 501–506.
Scholander, P. F., Hock, R., Walters, V. and Irving, L. (1950). Adaptation to cold in arctic and tropical mammals and birds in relation to body temperature, insulation, and basal metabolic rate. Biol. Bull. 99, 259–271.
Spandagos, C. and Ng, T. L. (2017). Equivalent full-load hours for assessing climate change impact on building cooling and heating energy consumption in large Asian cities. Appl. Energy 189, 352–368.
Taleb, H. M. (2014). Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings. Front. Archit. Res. 3, 154–165.
United Nations Environmental Program (UNEP). Buildings and climate change: a summary for decision-makers; 2009.



Pathogens and the Anthropocene: Germs, Genes, Geography, Part 2

[This is the continuation of the post from last week.]

To speak of an “Anthropocene for pathogens” is to imagine the ways that human transformation of the environment has shaped the ecology and evolution of infectious microbes. In other words, it is to imagine Continue reading

Pathogens and the Anthropocene: Germs, Genes, Geography, Part 1

The smallpox virus

We welcome our colleague Kyle Harper to the blog; his bio is on the OU contributors page. His book, The Fate of Rome: Climate, Disease, and the End of an Empire, is now available from Princeton University Press. Continue reading

Early Cities and Other Urbanisms

Galata bridge in Istanbul, bridging east and west, old and new. By Moyan Brenn [CC BY 2.0)]

Urban landscapes provide useful spaces for thinking through the complexities of the Anthropocene. They are hybrid locations in which the social and ecological Continue reading

Urban Ecology

The male showed up with breakfast.

A post shared by Dacey (@officebuddha) on

As we get started with our series on the urban Anthropocene, I’d like to approach the topic as a biologist, and think of cities as places filled with various kinds of life.
Continue reading

Et in Arcadia ars: Thoughts on Volcanism and Urbanism in Southern Italy, Part Two

[This is the continuation of the post from last week.]

The Plain of Catania, atop which the city of Catania sits, is land reclaimed from the Ionian Sea by Etna’s lava and other subterranean volcanic uplift. Johann Wolfgang Goethe, who traveled across it while writing the letters and notes that became his Italian Journey, refers quite accurately on May 1, 1787 to Continue reading

Prospection and the Anthropocene

I’d like to share two recent items from the news that make a sobering pairing.

The first is an opinion piece in the New York Times by psychologist Martin Seligman and Times science writer John Tierny summarizing a new theory about human beings that emphasizes our orientation toward the future. Continue reading

Weedy Resistance: Multispecies Tactics for Contesting “The Age of Man”

We welcome Ellie Irons, an artist and educator based in Brooklyn, NY, as a guest on the blog . . . click for her own website, or see her bio under the “Who we are” tab.

resistance (Biology): Ability (of an organism, tissue, or cell) to withstand a destructive agent or condition such as a chemical compound, a disease agent, or an environmental stressor. (American Heritage® Medical Dictionary) Continue reading

An Age of Trump in the Anthropocene Epoch?

Stratigraphy is the science of rock strata; in geological terms, this translates to the science of time. But what IS time? Difficult to define, for certain, but most of us can agree that it marks the passage of events. We experience the passage of Continue reading

Loving the Anthr*pocene

My previous post was a provocation on refusal.  How, I asked, might the Anthr*pocene concept naturalize and even magnify the violent, dispossessionary forces it purports to describe?  And how might refusing this concept relate to Continue reading

The Iconoclastic Anthropocene: On How We Choose to Destroy Art

Ivo Bazzechi Cimabue FloodOn November 4, 1966, the Arno overflowed its banks into the streets of Florence. A number of prominent foreign art historians, including Frederick Hartt and John Shearman, arrived soon thereafter to assist their Italian colleagues, working generally under the oversight of the Uffizi’s conservation director Umberto Baldini, in developing a response to a cultural emergency: the Italian Renaissance was underwater. Their collective expertise facilitated the arduous work of restoring what could be salvaged from the flood, which had Continue reading

The Roles for Indigenous Peoples in Anthropocene Dialogues: Some Critical Notes and a Question

We welcome Kyle Powys Whyte, of Michigan State University, as a guest on the blog . . . click for his bio, or go to the “Who we are” tab.

I bet there have probably been more than a hundred events organized for the purpose of fostering dialogue of all kinds on what meanings and futures are presupposed by the “anthropocene.” I have been to some of them. I even just Continue reading

New Year’s Greetings for 2017




In this season of the solstice, the natural world reminds us that at the darkest moment light can return. But our own nature is such that brighter days in the human sense are not inevitable–they must be strived for and accomplished.  Here’s to the joy of imagining, and working toward, a truly habitable future.

CRISPR as Niche Construction: an Aristotelian View

CRISPR (pronounced “crisper”) is part of a system, noticed in certain bacteria, by which a cell can make changes in strands of DNA. This mechanism appears to be a proto-immune system: it enables a bacterium to recognize Continue reading