Today: Rising ocean temperatures
The Challenger expedition provides direct evidence of rising ocean temperatures.
The longest interval over which records of ocean temperatures can be compared on a global scale is the 135 years between the voyage of HMS Challenger (1872-1876) and the modern data set of the Argo Programme (2004–2010), whose floating devices continuously measure the temperature and salinity of the ocean. The study, reported in Nature, underlines the scientific significance of the Challengerexpedition and the modern Argo Programme and indicates that globally the oceans have been warming at least since the late-nineteenth or early-twentieth century. https://www.nature.com/articles/nclimate1461
During the Challenger’s four-year expedition it stopped 354 times to take soundings of ocean temperature and salinity. For example, on September 8th 1875 at Sounding Station number 272 (see chart), the ocean’s surface temperature was 79 degrees Fahrenheit (26.1 degrees Celsius), and on the sea floor the temperature measured 35.1 degrees Fahrenheit (1.7 degrees C), at a depth of 2,600 fathoms (15,500 feet).
Compared with Challenger’s sparse but pioneering measurements, across the globe today some 4,000 Argo floats continuously collect and transmit data on the temperature and salinity of the ocean. Once deployed, an Argo floats, sinks to 1000 meters, drifts with the ocean currents, sinks a further 1000 meters, and then resurfaces to transmit its data to a satellite. The batteries last four years.
Argo floats: Ocean Challenge, 2019, vol. 23 no.2.
The study, the first global-scale comparison of Challenger and modern data, shows average warming at the surface waters of the ocean of some 0.6 degrees Centigrade. Warming in the Atlantic Ocean was found to be stronger than in the Pacific Ocean.
Challenger Soundings, August-September 1875: Challenger Report.
Sources
Report of Challenger expedition: https://www.19thcenturyscience.org/HMSC/HMSC-Reports/1885-Narrative/htm/doc1014.html
135 years of global ocean warming between the Challenger expedition and the Argo Programme: https://www.nature.com/articles/nclimate1461
From HMS Challenger to Argo and beyond, Judith Wolf and Colin Pelton, Ocean Challenge, 2019: https://www.challenger-society.org.uk/oceanchallenge/2019_23_2.pdf