Conclusion

The GHE change was probably initiated at the end of the preindustrial period (around 1750) such that, since the early 20th century, surface temperatures of oceans and lands have reflected the global warming trend [Jones et al., 1988, Jones, 1994]. A radiative forcing of 2.45 was calculated for year 1992 [IPCC, 1995] from alterations in the atmospheric concentration of radiative components. Most of the estimated change apparently dates from the 1940s, but until now no direct proof has been provided. Our calculated change in radiative forcing of 1.74 between 1940 and 1995 over the Mediterranean area is comparable to that estimated from the curve of change with time over the northern hemisphere [IPCC, 1995], about 1.7 during the same period. Consequently, we believe that the trend of increasing temperature observed in the Mediterranean constitutes the first measured effect of the GHE change. Furthermore, the effect is quantifiable as well as its consequences on air temperature and freshwater budget in the Mediterranean area, where recurrent droughts and freshwater availability are already a problem. Improvement of results requires more marine and climatic data and a special attention to different simplifying hypotheses used in this first attempt. Nevertheless, the calculated changes in heat and freshwater budgets, i.e a 2.5% decrease of the longwave radiation and 10% change in freshwater budget, appear sufficient [Béthoux and Gentili, 1997] to explain the dramatic change in water mass formation and distribution in the eastern Mediterranean [Della Vedova et al., 1995, Roether et al., 1996]. Once again, the Mediterranean appears as a scaled down model for the study of ocean circulation and environment - air - sea interaction, and the monitoring of climatic and environmental evolutions, changes with consequences for the Mediterranean ecosystem, marine circulation and the global change [Johnson, 1997].