Sustaining Ocean Observations to Understand Future Changes in Earth’s Climate

The ocean is an integral component of the Earth’s climate system. It covers about 70 percent of the Earth’s surface and acts as its primary reservoir of heat and carbon, absorbing over 90 percent of the surplus heat and about 30 percent of the carbon dioxide (CO₂) associated with human activities, and receiving close to 100 percent of fresh water lost from land ice. Heat and CO₂ are absorbed at the ocean’s surface and transported throughout the ocean depths through the overturning circulation. Although exchange across the ocean’s turbulent surface boundary layer can happen rapidly, in hours or days, and significant exchange of water between the boundary layer and the stratified main thermocline occurs over timescales of years to decades, deep water takes many decades to millennia to return to the surface, acting as long-term storage for heat and CO₂ and thereby lessening the near-term impacts of climate change. Because of the long timescales governing the exchange of heat, carbon, and fresh water in the ocean, long-term observational datasets spanning many decades are required to fully document, understand, and predict the climate system, and to detect and attribute changes driven by human activities.