January 24, 2023 — Maine’s Department of Marine Resources has maintained a hidden treasure in Boothbay Harbor for nearly 120 years — a daily measurement of sea surface temperatures, which provides an uncommonly long record of a warming ocean.
In the latest Data Monitor, The Maine Monitor broke those daily records (more than 42,000 of them!) into annual averages to show the estimated increase in water temperatures at Boothbay Harbor between 1905 and 2021. It shows a rough increase of 4 to 5 degrees Fahrenheit on average, from an annual average of 45.3 degrees F (or 7.4 Celsius) at the turn of the 20th century to just over 50 degrees F in recent years.
One important caveat on this data: DMR’s method for collecting the water temperatures in the harbor changed around 1950. Before, measurements were taken three times a day, during the day, using a thermometer in a bucket lowered into the water. In the 1950s, this was replaced with instruments installed just below the surface to take continuous measurements.