Sea surface temperature is the measure of thermal energy in the upper layer of the ocean. This measurement is not taken at a single, uniform depth but varies based on the method used. It provides a snapshot of the ocean’s condition, influencing everything from local weather to global climate patterns. Understanding this metric is important for comprehending the relationship between the Earth’s oceans and atmosphere.
How Sea Surface Temperature is Measured
A global picture of sea surface temperature requires combining data from multiple sources. Since the 1980s, satellites have become the primary tools, providing extensive coverage impossible with surface-level instruments alone. These satellites are equipped with radiometers, including infrared and microwave sensors, which detect thermal energy radiating from the ocean. Infrared sensors offer high spatial resolution but cannot see through clouds, while microwave sensors can penetrate cloud cover but provide data at a lower resolution.
To complement satellite observations and ensure accuracy, scientists rely on in-situ measurements. These are collected by a network of instruments, including moored and drifting buoys that record temperature around one meter below the surface. Ships also contribute by using hull-mounted sensors to measure the temperature of water flowing into the engine room. By integrating satellite and in-situ data, researchers create comprehensive daily maps of global sea surface temperatures.
Natural Drivers of Temperature Fluctuation
The primary natural driver of sea surface temperature is solar radiation. The sun’s energy heats the ocean’s surface, with the most intense warming occurring in tropical regions where sunlight is most direct. This heat is redistributed across the globe by ocean currents. Systems like the Gulf Stream act like conveyor belts, transporting warm water from the tropics toward the poles and cycling colder water back toward the equator.
On a shorter timescale, phenomena like the El Niño-Southern Oscillation (ENSO) cause substantial fluctuations in the tropical Pacific Ocean. During an El Niño event, trade winds weaken, allowing warm water to accumulate in the eastern Pacific, which raises sea surface temperatures. Conversely, La Niña events involve stronger trade winds that push warm water westward, bringing cooler, deeper water to the surface in the east. These recurring patterns have a significant impact on the ocean and global weather.
Influence on Weather and Climate
The temperature of the ocean’s surface has a strong influence on weather and climate systems. Warm ocean water, particularly temperatures above 27°C (80°F), acts as the primary fuel source for hurricanes. As water evaporates from the warm ocean, it transfers heat and moisture into the atmosphere. This process, known as a heat engine, releases energy as the water vapor rises and condenses, intensifying the storm’s wind speeds.
This exchange of energy between the ocean and atmosphere also dictates broader climate patterns. Warmer sea surfaces lead to higher rates of evaporation, which can result in more intense rainfall and flooding in some regions. For instance, human-caused warming has been found to increase extreme rainfall rates during hurricanes. The distribution of warm and cool water across ocean basins influences atmospheric pressure systems, steering storm tracks and contributing to conditions like droughts or heavy precipitation.
Effects on Marine Ecosystems
Changes in sea surface temperature have significant consequences for marine life. One of the most visible impacts is coral bleaching. Corals have a symbiotic relationship with microscopic algae called zooxanthellae, which live in their tissues. When water temperatures rise even slightly for a prolonged period, corals become stressed and expel these algae, causing them to turn white and leaving them vulnerable to disease and starvation.
Warmer waters also compel many marine species to alter their geographic ranges. Fish, marine mammals, and other mobile organisms often migrate toward the poles in search of cooler, more suitable habitats. This migration can disrupt established food chains and lead to overcrowding in new environments, altering the structure and health of marine ecosystems.