**4.4 Sea surface temperature**

The thermometer measurements made on water samples taken by merchant and navy ships as they sailed the world's oceans date back to about 1850, and constitute the instrumental record of natural processes within the oceans. The data is best for parts of the oceans along major trading routes, and it's understandable that they are scarcer further back in time. These readings, like those from land-based meteorological observation posts, must be gridded to provide a global average sea surface temperature. Since the oceans cover about 75% of the earth's surface, the sea surface temperature record is close to global temperature records, as one would expect (**Figure 7**).

The two records are identical, but the SST (sea surface temperature) varies across a narrower spectrum than the land surface temperature, and the land temperature are subjected to dramatic swings. This disparity is primarily due to the oceans' higher heat potential than the air (it takes a long time to heat and cool the oceans).

The measurement and data collected from hundreds of buoys stationed across the ocean at the depth range of about 2000 m collected over the years as early as 1955, showed that not just the surface of the oceans but the whole upper half of the ocean is gradually warming. Over the past 50 years average of 0.1 to 0.2°C was recorded. So, while the whole ocean has absorbed a huge amount of heat, its overall temperature has changed little. Nevertheless, the very surface of the ocean has warmed almost as much as the rest of earth's surface [26]. Thus, form the past data and the present data it shows that the oceans are warming up slowly which almost resonates with the increase in land surface temperature, indicating the occurrence of global warming.

Analysis of four dimension (indictors) indicates the happening of global warming. The connection between the global warming and climate change is well documented. For instance, according to IPCC [27] "Changes in many extreme weather

**Figure 7.** *Comparison of Sea surface temperature and land surface temperature (source: Brawlower and Bice [26]).*

and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions" (p.7). Moreover, IPCC [15] predicts differences in mean temperature in most land and ocean regions, hot extremes in most inhabited regions, heavy precipitation in several regions, and the probability of drought and precipitation deficits in some regions, caused by the phenomenon of global warming.
