Over the last century, accumulation of greenhouse gases like carbon dioxide and methane from anthropogenic activities have resulted in increasing atmospheric temperature. Oceans are also warming as they absorb additional heat from the atmosphere. Increases in temperature are most pronounced in the surface layer and the high latitudes of the ocean.

Temperature is a fundamental driver of physiology, in that it affects almost all metabolic processes. The effects of increasing temperature are studied in physiological, ecological and evolutionary experiments; a large literature of experiments and theory on organismal responses to high and rising temperature exists, and this is still one of the main areas of investigation in global change biology.

Physical and chemical interactions with other drivers: Warming increases stratification in water columns, which reduces vertical mixing. This, in turn, reduces the delivery of nutrients from deep to surface waters. Warming reduces dissolved gas levels (such as oxygen) in seawater. Warming can also reduce salinity through ice melting.

References and resources

• A hierarchical approach to defining marine heatwaves
  Hobday et al., 2017, Progress in Oceanography, doi: 10.1016/j.pocean.2015.12.014