Physical and chemical changes in the ocean over basin-wide zones and decadal or longer time-scales: perspectives on current and future conditions - Ocean Sustainability in the 21st Century - page 81

3.2 Ocean warming
Ocean temperatures and air-sea fluxes play a key role in regulating physical and biological
systems. Storage and transport of heat in the ocean are central drivers of the global energy
budget (Church et al ., 2011 ; Levitus et al ., 2012 ) . They influence slow climate variability
such as El Niño (Zebiak, 1989 ) and the North Atlantic Oscillation (Curry and McCartney,
2001 ) , and influence storm tracks and moisture flux across the oceans (Hoskins and Hodges,
2002 ) . Expansion due to warming is a major contributor to sea-level rise (Johnson and Wijf-
fels, 2011 ; Church et al ., 2011 ) . Increasing temperatures contribute to upper layer stratific-
ation, and thus may alter nutrient supply to primary producers (Barber, 2007 ) . Ocean tem-
peratures also set thermal range limits for fish (Pörtner and Farrell, 2008 ) and conditions for
species invasion (Occhipinti-Ambrogi, 2007 ).
Overall the global ocean has warmed significantly during the period of instrumental re-
cords (Levitus et al ., 2012 ) . For example, the ocean mean temperature in the 0-2000 m layer
increased by 0.09 °C over the period 1955-2010, and global mean sea surface temperature
(SST) increased by 0.67 °C over the last century (Rayner et al ., 2006 ). Warming in most
LMEs accelerated in the late 1970s/early 1980s. Approximately two thirds of the increase in
ocean heat content during 1955-1998 occurred in the upper 700 m, with patterns of change
having clearly defined basin-wide scales (Levitus et al ., 2012 ).
The increase in ocean heat content is much larger than in any other store of energy on
Earth over the assessed periods 1961-2003 and 1993-2003 and accounts for approximately
93% of the increase in heat content of the Earth system (Levitus et al ., 2012 ). Ocean heat
content variability is therefore a critical variable for detecting the effects of the observed
increase in greenhouse gases (GHG), and for resolving the planet's overall heat and energy
balance.
Satellite observations of LMEs show SST warming in 61 out of 64 domains, ranging
from 0.08 °C (Patagonia) to 1.35 °C (Baltic Sea). Relatively rapid warming of 0.6 °C was
found in middle and high-latitude LMEs over the past 25 years. Warming exceeding 0.96 °C