Climate-Driven Physical and Chemical Changes in Marine Ecosystems

Covering more than two-thirds of the Earth’s surface, the oceans are a central component of the global climate system. The oceans help to control the timing and regional distribution of the Earth’s response to climate change, primarily through their absorption of carbon dioxide (CO2) and heat. Changes to the physical and chemical properties of the oceans are already being observed. Sea surface temperatures are warming, sea level rise is accelerating, the oceans are becoming increasingly acidic, and the rate of sea ice melt is steadily increasing. The International Panel on Climate Change (IPCC) assessment released in 2007 projects that, due to the persistence of greenhouse gases in the atmosphere, it is highly likely that the oceans will continue to warm and the impacts will be felt for centuries (IPCC, 2007a). This section focuses on the physical and chemical changes currently being observed in the Earth’s oceans, including changes in temperature, stratification, salinity, sea ice, climate regimes, ocean circulation, and ocean acidification. Knowledge gaps and research needs will be discussed throughout. The aim is to assess the current state of knowledge related to how climate change may be interacting with, and in some cases, driving, the observed physical and chemical changes in the Earth’s oceans, and what that means for the U.S.