Suphat Vongvisessomjai

pp. 431 - 444

Abstract

The earth absorbs much radiation from the sun to warm the atmosphere, the land, and the oceans. This energy is reradiated back into space. In the past, the thermal budget of the earth is more or less balanced, with radiation from the sun on
par with thermal radiation from the earth. With increasing greenhouse gases in the atmosphere, some of the thermal radiation
is absorbed by these gases resulting in an increase of global mean surface temperature, melting of polar ices and thus
contributing to a rising of sea level. However, sea-level changes depend upon four main processes: 1) Glacio-eustasy, 2)
Emergence/subsidence of land, 3) Man-made activities, and 4) Ocean-atmosphere effects. The assessment report of the Intergovernmental Panel on Climate Change (IPCC, 1990), which was based on past data in Europe and the USA, including the
North Atlantic Ocean, published a mean temperature of 14°C and an actual increase of 1°C in the last century, plus an increase
of CO₂
 from 370 ppmv to 550 ppmv, and a three-fold temperature increase of 3°C in this century. All these changes are projecting a sea level rise (SLR) of 31-110 cm per century on global scale, which was in fact applicable to the North Atlantic. The
assessment report of the IPCC Working Group I (1996) has realized that differential SLR occurs due to different geographical
conditions. It identified ten regions on earth and compared the actual climate change to what it was postulated to be, and
came up with SLR of 15-95 cm per century. The assessment report of the IPCC Working Group II (2001) employed improved
data obtained from tide gauges and satellite images as well as mathematical model results with the most convincing evidence
in the North Atlantic, and it concluded an SLR of 9-88 cm per century. But it had, however, noted a lack of data in the Pacific
and Indian Ocean. The assessment report of the IPCC Summary for Policy Makers (SPM, 2007) that included six different
arctic and antarctic climate science scenarios reported relatively lower value of 18-59 cm per century. The North Atlantic that
is surrounded by glaciers might see a SLR due to ice melting related to an increase of the temperature in the Atlantic Ocean.
Nevertheless, the lack of data on global warming in the tropics especially in the Pacific and the Indian Oceans, which have
no glaciers, might put a different view on the conclusions derived from temperature and arctic data. Six decades of comprehensive information from the Gulf of Thailand regarding oceanographical and meteorological data is revealing a much lower
SLR. The mean monthly sea levels in six decades at Sattahip and Ko Lak showed no increasing trend, while those rises at
Samut Prakan and Samut Sakhon are due to land subsidence from excessive groundwater pumping.