Note: this is an abbreviated repost of an article I wrote for my Economic Development class that I’ll be using for a guest lecture on climate change.
Humans co-evolved with our technological inventions for warming up in the cold: fire, shelter, and clothing. Our large brains would not work without the precise temperature regulation provided by our nearly furless skin. Even the remnant fur on our heads is there to insulate the most temperature-critical body part by shading it from intense sun and warming it from the cold while the naked skin on the rest of our body can radiate out the enormous heat created by our brains. Although our brains are only about 2% of body weight, they generate 20% of the heat of our bodies and they don’t work well if they overheat. Brains must be kept within a very narrow temperature range to work correctly. Because human skin is better at eliminating heat than retaining it, humans have needed heating technologies to survive even moderate cold snaps: fire, shelter, and/or clothing.
Whereas humans have always had technologies for warming up, it was not until the 1950s that humans had an equally reliable technology for cooling down when trying to work in a place that is too hot. And cooling down is crucial for our brains to function well. Witness our naked bodies for evidence. Before the air conditioner, people could not work when the weather gets too hot. They were forced to siesta during the heat of the day or migrate into the cool of the mountains during hot seasons. Here is an estimate from NOAA of how much less time humans can do physical labor outside in the tropics compared with temperate zones:
By their estimate, people in the tropics can’t spend as much time doing physical labor as in the temperate zone where people can spend roughly 50% to 300% more time working. The bottom graphs shows that this would get much worse with 3 degrees of global warming.
Throughout history, observers have noticed that cooler geographic regions have been richer than hot regions. For example, the richest part of the globe is the temperate zone in the northern hemisphere, but even in the southern hemisphere, the richest part of Brazil is its temperate south, the richest part of Africa is its temperate south and the same goes for Australia. Even in tropical countries like Mexico, Bolivia, and Ethiopia, the majority of economic activity is at high altitudes where the temperatures are cool. Whereas the majority of the Mexican population lives above 5,000ft, most people in temperate nations prefer to live in lowlands near bodies of water. The island states of Indonesia and the Philippines have a lot of economic activity, but much of this territory is surprisingly temperate due to temperate ocean breezes or high altitudes as you can see in the following map which comes from 2001 research by Sachs, Mellinger, and Gallup.
They discovered that 8.4 percent of the world’s inhabited land area, produces 52.9 percent of the world’s income. The blessed geography of wealth is the temperate zone within 100km of an ocean-navigable waterway. Per-capita income is 2.3 times greater than the global average in this region. Being in a temperate zone has been an economic blessing that accounts for a lot of why some places are richer than other places. Global warming will expand the zone of tropical weather and shrink the cool temperate zone. Fortunately, we have some reason for optimism: the air conditioner.
The southern US is the poorest region of America has been for all of history, but since the spread of the air conditioner in the 1950s, it has been growing faster and it is finally catching up. Ed Glaeser found that the two main factors that are correlated with regional population growth in the US after 1960 are warmth in winter and the prevalence of college educated workers. The air conditioner is the main reason why the south has been the fastest growing region of the US since 1960.
For example, the Cleveland Fed made a graph showing how the air conditioner contributed to shrinking cold-weather cities and growing hot-weather cities:
Cooler working temperatures simply make people more productive. In Caribbean nations, short-term drops in temperatures are correlated with large increases in GDP. Cooler temperatures seem to reduce crime and make people less impatient and violent. Air conditioners can bring higher productivity and patience to any climate, but even with modern air-conditioning, extreme heat reduces economic output even in the US:
Tatyana Deryugina and Solomon Hsiang find that hot days are bad for the economy — not just in poor countries with an overwhelmingly agricultural workforce, but in the United States of America. Here in the US, “productivity of individual days declines roughly 1.7% for each 1.8°F increase in temperature above 59°F.” That means that “a weekday above 30°C (86°F) costs an average county $20 per person.”
…Hot days kill growth both because of negative impacts on agriculture and because it seems that, despite air conditioning, people simply work less efficiently when it’s hot. …Extreme cold is unpleasant, but as a society we can live through it and even thrive. Extreme heat saps our will to live in a more fundamental way, crushing the economy and driving long-term immiseration.
Before the air conditioner, heat waves were deadly in the US. Now they are more of a mere annoyance that keeps people inside.
The above graph shows that before the air conditioner (red line), heat waves caused mortality spikes. Since 1960, relatively few Americans have been unable to escape the heat and have had problems. Because most Indians are too poor to afford air conditioning, they still have large mortality spikes during heat waves.
Tragically, the idea for mechanically cooling living space was invented in the 1840s by John Gorrie, but didn’t take off. Unfortunately, he was unable to get financial backing and died bankrupt. He marketed it as a remedy for malaria and yellow fever because he believed in the common theory of the day that malaria was caused by bad air (which is literally what the word ‘malaria’ means) and he believed that cooling the air could keep the poisonous gasses away.
Perhaps his idea was ahead of its time, but he might have just been targeting the wrong market. He might have been more successful if he would have marketed it for industrial and luxury markets because that is how Willis Carrier succeeded when he reinvented the air conditioner a second time in 1902. He initially found success selling them to printing and textile factories to stabilize the humidity that wreaked havoc with production and that focus on humidity is why they got the name air conditioners rather than air coolers. Nobody tried using them to cool the air merely for human comfort until the first residential unit was installed in 1914 in Minnesota (of all places) and they became popular in the 1930s in movie theaters and finally revolutionized life in the sunbelt in the 1950s as the technology improved and costs dropped.