For the first time, scientists have used ocean measurements taken on research voyages almost 150 years ago to learn more about how human activity has impacted climate change.
Scientists from the U.K. National Oceanography Centre (NOC) and the Scottish Association for Marine Science (SAMS) have made the first combined study of water density measurements from the British HMS Challenger and Prussian SMS Gazelle round-the-world research expeditions in the 1870s to draw parallels with modern-day measurements. The two ships, which circled the world independently, provided new insights into the ecologies and ethnologies of remote and rarely visited communities and of the biology, geology, physics and chemistry of the oceans.
Their two contributions have been brought together to give an insight into the impact of the Industrial Age on Earth’s climate. The study is the first global-scale analysis of salinity from these two expeditions and the first observational evidence of changes in the global water cycle since the late 19th century.
The findings, published in the journal Nature Communications in Earth and Environment, confirm that there has been an increase in evaporation from saltier parts of ocean, such as the Atlantic, and more rainfall in fresher areas. In effect, changes in the salinity pattern of the oceans have been used as a global-scale rain gauge.
Now this trend has now be found to extend back to the 1870s, early in the Industrial Age, and to have been 50% less intense before the 1950s than since that decade.
The water cycle is extremely sensitive to environmental changes. A rise in global temperature of just one degree Celsius will result in a 7 to 8% increase in water vapor in the atmosphere.
Earth’s average temperature has warmed by over 1°C since the 1950s, and this accelerates the water cycle. Patterns and intensity of rainfall over land are changing, and deserts are expanding.