The climate system envelops our planet, with swirling fluxes of mass, momentum, and energy through air, water, and land. Its processes are partly regular and partly chaotic. The regularity of diurnal and seasonal fluctuations in these processes is well understood. Recently, there has been significant progress in understanding some of the mechanisms that induce deviations from that regularity in many parts of the globe. These mechanisms include a set of combined oceanic–atmospheric phenomena with quasi-regular manifestations. The largest of these is centered in the Pacific Ocean and is known as the El Niño–Southern Oscillation. The term “oscillation” refers to a shifting pattern of atmospheric pressure gradients that has distinct manifestations in its alternating phases. In the Arctic and North Atlantic regions, the occurrence of somewhat analogous but less regular interactions known as the Arctic Oscillation and its offshoot, the North Atlantic Oscillation, are also being studied. These and other major oscillations influence climate patterns in many parts of the globe. Examples of other large-scale interactive ocean–atmosphere– land processes are the Pacific Decadal Oscillation, the Madden-Julian Oscillation, the Pacific/North American pattern, the Tropical Atlantic Variability, the West Pacific pattern, the Quasi-Biennial Oscillation, and the Indian Ocean Dipole. In this chapter we review the earth’s climate system in general, define climate variability, and describe the processes related to ENSO and the other major systems and their interactions. We then consider the possible connections of the major climate variability systems to anthropogenic global climate change. The climate system consists of a series of fluxes and transformations of energy (radiation, sensible and latent heat, and momentum), as well as transports and changes in the state of matter (air, water, solid matter, and biota) as conveyed and influenced by the atmosphere, the ocean, and the land masses. Acting like a giant engine, this dynamic system is driven by the infusion, transformation, and redistribution of energy.
Sea surface temperature anomaly in the tropical North Atlantic during El Niño decaying years