What ancient Chinese roofs can tell us about climate change

To reconstruct a picture of past climates, scientists often examine trapped bubbles in ice cores or the width of rings in old trees. A new study, published in Science Advances by researchers at Nanjing University in China, suggests there may even be evidence of past changes in weather conditions in buildings.

The researchers compared data on changing weather patterns between AD750 and 1750 with examples of preserved roofs built in China during the Millennium. They found that during periods of heavier snowfall, roofs were built with steeper slopes, while warmer periods gave rise to buildings with more gently sloping roofs.

The study covered two major fluctuations in global climate: the Medieval Warm Period, which ran roughly from the 10th to the 13th century, and the Little Ice Age, which saw shorter summers and bitter winters between the 15th and 19th centuries.

A chart with four different roof designs and height ratios according to warm and cold periods.
Four typical roof designs from four different climatic periods.
Li et al. (2021) / Scientific progress

Changing weather patterns may also have spurred innovation, as the researchers note that frigid weather around 1700 coincided with new methods that made the construction of steeper and straighter roofs safer and more reliable.

It’s incredible to think that something as subtle as the angles of pitched roofs can be an intimate reflection of changes in weather over ten centuries. It’s a compelling story, but as someone who has studied architectural history for years, I have my doubts.

Architecture and the climate

The researchers made two basis points. First, that roofs are built steeper over eras and in places of heavier snowfall. And two, that there is a close correlation between weather patterns and roof angles, revealing a sensitivity in architecture to very small changes in climate.

The first point is quite easy to prove and probably undisputed among academics. A carpenter corrects the roof angle once a building has collapsed under heavy snowfall, and it has his credit to show this with the example of historical buildings in China.

The second point, in my opinion, has not been coherently proven by this study and may even be impossible to prove. The researchers cite studying about “200” [building] remains over a millennium”, but it is not clear whether these are equally distributed over the study period. They could get away with it as historians, as opposed to, say, physicians, where sample size is the litmus test of sound methodology.

It is also unclear why roofs should be less steep in warm times. However, the researchers should be commended for their efforts to address this issue, as the study notes that Chinese may not have been able to maintain steeper roofs during times when snowfall was less severe due to “cost and the varying need for shelter.” against sunshine and rainfall”. However, the researchers do not develop this point and do not explain why flatter roofs should be more cost-effective.

However, building a roof is not a collective event such as population decline, infant mortality or market prices. It depends on the conscious decision of a particular person – a customer, architect or craftsman. To prove a link, the researchers would need a theory about how builders might respond to small changes in climate with small changes in roof angles. Exaggerating this climate connection in architecture could falsely imply that premodern societies were shaped primarily by an inexplicable harmony between humans and nature, with the ability to respond to minor environmental changes lost in later periods.

Small wooden buildings covered with thick snow.
Heavy snowfall calls for roof structures that do not collapse under pressure.
Lu Yang/Shutterstock

Such fine-grained reactions between building and weather do not happen in the present as far as I know. Snowfall became lighter and less frequent in the UK over the 20th century, but it would not be convincing to link this to the proliferation of modern flat roofs, which have become just as popular in snowy Russia. And even a fundamental decision, such as choosing between a flat roof or a pitched roof, seems to defy climatic needs, as the deplorably high rate of flat roof leaks in rain-ravaged Glasgow where I live shows.

Nevertheless, the study provides an eloquent reminder of how natural variation in weather has influenced architecture throughout history, often as much as changing styles and tastes.

Most of the buildings in which we live, work and socialize have been designed with little regard for the unprecedented weather extremes that climate scientists are warning this century. That will have to change. Historians may one day study the era we live in and note how architecture regained a sense of environmental limits, as leaky and inefficient designs were swept away by buildings able to withstand increasing storms.

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