Ocean warming

Figure 1. Time series of upper ocean heat content (1022) for the upper 700m (IPCC 2007)
The oceans are warming:
  • Ocean temperature has increased by 0.1oC between 1961 to 2003 from the surface to a depth of 700m
  • Ocean heat content has increased over the upper 3000m over the same period, equivalent to absorbing a heating of 0.21±0.04 Wm-2.
  • The oceans have absorbed 80% of the extra heat added to the climate system.
There are also signals of associated changes in the salt content: 
  • global freshening of sea water at high latitudes and salinification of the shallower parts of the tropical latitudes.
These trends are consistent with changes in precipitation and an increased atmospheric transfer of freshwater from the tropics to high latitudes.At present, there is no clear evidence of circulation changes, including the Gulf Stream and ocean overturning. It is predicted that there will be a weakening of the ocean overturning, which is being monitored by the UK NERC RAPID programme. 

Example of work at Liverpool

Changes in how the ocean stores heat has been assessed using historical temperature and salinity data from 1950 to 2000.  The ocean is not warming in a uniform manner, instead there are reversing patterns of warming and cooling. For example, between two twenty year periods from 1950 to 1970 and 1980 to 2000, the ocean is particularly warming in the tropics and subtropics, and instead cooling in the subpolar latitudes (Figure 2). The changes in the ocean heat storage are due to a combination of air-sea heat fluxes and an ocean redistribution of heat induced by the wind. The pattern of these ocean heat content changes often reverses in time and does not reflect a long term climate trend. This work was conducted in collaboration with scientists at Duke University.

Figure 2. Ocean heat content changes (1020J, red is warmer and blue is cooler) between two twenty year periods, 1950 to 1970 and 1980 to 2000. These heat content changes reflect changes in air-sea heating and a redistribution of heat within the ocean due to the effect of the winds. Further details see Lozier et al. (2008).
 

Presentations in the Marine Sciences Symposium 2008 'Climate change: the science and the impacts - a Liverpool perspective' by

References (and links)

  • IPCC, Climate change 2007: The Physical Science Basis. Contribution of Working group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK and New York, USA, 2007.
  • Leadbetter, S.J., R.G. Williams, E.L. McDonagh and B.A. King, 2007: A twenty year reversal in water mass trends in the subtropical North Atlantic. Geophysical Research Letters, 34, L12608, doi:10.1029/2007GL029957.
  •  Lozier, S., S. Leadbetter, R.G. Williams, V. Roussenov, M.S.C. Reed and N.J. Moore, 2008. The spatial pattern and mechanisms of heat content change in the North Atlantic. Science, 319, 5864, 800-803, doi: 10.1126/science.1146436 
  • Wind patterns mask global warming effects (Research Intelligence, Issue 34, Spring 2008)