The Pressure Is On: From Whales to Conservation

Ships were often outfitted with a barometer, which would be able to indicate fair or foul weather based on atmospheric pressure. Source: Mystic Seaport

A thick layer of fog and mist has settled over Cape Cod Bay, rendering visibility difficult as the Morgan departs Provincetown for the bustling city of Boston, Massachusetts. While these conditions would be slightly disconcerting to the inexperienced sailor, the crew have likely predicted the poor visibility through a well-worn piece of weather equipment known as a barometer, which will allow them to adjust their sailing plan accordingly. The barometer is used to measure air pressure, also known as barometric pressure. In addition to wind speed and direction, this is a useful measurement in forecasting short-term weather changes.

Though Italian physicist Evangelista Torricelli is credited with the invention of the barometer in 1643, historical documentation of other European scientists suggests that interest in the link between weather conditions and pressure was widespread both before and after that time. Whalers were no exception. Ship logs contained, if not an exact barometer reading, descriptions of weather conditions as the ships passed through different pressure systems. Modern climatologists have taken advantage of such diligent recordings to detect long-term weather trends.

One new project, known as the “Old Weather Project,” reflects Lieutenant Maury’s philosophy of citizen science. Through the easily accessible website interface, online volunteers assist in exploring, marking, and transcribing 19th and 20th century ship logs. Once entered, the data can then be used by supercomputers that run sophisticated climate models. The Old Weather Project focuses largely on creating these models based on observations from whaling logbooks, which are perhaps the only source of historical information on barometric pressure and weather patterns.

Today, weather maps still mark areas of high and low pressure to predict the forecast. Source: Wikimedia Commons

Barometric pressure is affected by a variety of variables, including the temperature of the air, the amount of water vapor it contains, and its proximity to the gravitational pull of the earth. Different combinations of these conditions produce different forms of weather. Many times, exposed sailors could actually feel a change in air pressure, even without access to a barometer. It became common whaling knowledge that low pressure brought storms and cooler temperatures, while clearer weather would appear when the pressure increased. Because daily observations of weather were often recorded during a voyage, logbooks can be used to deduce the frequency and location of different pressure systems over time. They provide an important historical baseline for examining climate change since the nineteenth century. In this era of technological innovation, the whalers leave a legacy that they never could have imagined.