Climate change increases water salinity primarily by causing warmer temperatures, which leads to increased evaporation of freshwater, leaving the salt behind.
The Impact of Warming on Water Salinity
The Earth's climate is warming due to increased greenhouse gas emissions. This warming directly affects the water cycle, particularly over large bodies of water like the ocean. Higher temperatures cause more water to evaporate from the surface.
As explained by Lijing Cheng in a statement from September 9, 2020, "Evaporation takes freshwater from the ocean into the atmosphere and increases the ocean salinity; precipitation puts freshwater into the ocean and reduces its salinity."
Here's a breakdown of how this works:
- Increased Evaporation: Warmer air can hold more moisture, and warmer water surfaces evaporate faster. Climate change drives up both air and sea surface temperatures, accelerating the rate of evaporation from the ocean.
- Freshwater Removal: When water evaporates from the ocean, the salt is left behind. This process effectively removes pure water (freshwater) from the ocean, concentrating the remaining salt.
- Increased Salinity: The removal of freshwater through evaporation, without a proportional increase in freshwater input (like precipitation or ice melt in certain regions), leads to an increase in the overall salinity of the remaining water body.
While precipitation adds freshwater back to the ocean and reduces salinity, climate change is altering global precipitation patterns unevenly. Some regions are experiencing more intense rainfall, while others face increased drought and reduced precipitation. This uneven change in the water cycle, combined with increased evaporation in many areas, drives significant shifts in ocean salinity.
Salinity as an Indicator
Because these changes in evaporation and precipitation affect large areas, salinity acts as a key indicator of broader water cycle alterations driven by climate change, as noted by Lijing Cheng: "Consequently, salinity changes integrate effects over broad areas and provide an excellent indicator for water cycle change.”
Essentially, where climate change leads to increased evaporation dominating over freshwater input, salinity rises. Conversely, where freshwater input (like intense rain or ice melt) dominates, salinity can decrease. However, the general increase in global temperatures fuels evaporation, making increased salinity a notable consequence in many ocean regions.
| Process | Effect on Salinity | Role in Climate Change Context |
|---|---|---|
| Evaporation | Increases Salinity | Enhanced by warming temperatures |
| Precipitation | Decreases Salinity | Changing patterns under climate change |
| Freshwater Influx | Decreases Salinity | Can be reduced in some regions (e.g., drought), or increased in others (e.g., ice melt) |
Changes in ocean salinity have significant implications for ocean circulation patterns, marine ecosystems, and sea level rise.
