Global Warming, Glacier Melt & Sea Level Rise: New Perspectives

Abstract

There is a heightened interest at present on the possibility of rapid melting of world-wide glaciers and ice caps (e.g., Greenland & Antarctic Ice Caps) as a result of ongoing global warming, which could lead to escalated sea level rise in future. Several stories and news items in the print & TV media and also in scientific magazines seem to strongly suggest that glaciers and ice caps are melting faster than ever and this could lead to significant rise in global and regional sea level. Recent popular Hollywood movies like An Inconvenient Truth showing big ice shelves breaking off and sliding down into cold Arctic Ocean seem to reinforce this perception that the ice caps and glaciers are indeed melting rapidly and causing sea level to rise dramatically. From a scientific perspective, satellite altimeter data (Topex/Poseidon) have estimated recent sea level rise of about 3mm/yr and possibly higher, this value being significantly higher than the traditionally held value of about 1.5 to 2 mm per yr (for most of the twentieth century) has generated sufficient interest among the scientific community about ‘escalating sea level rise’ in near future. In a recent (Journal of Climate 2007) paper, the lead author Prof (Emeritus) Carl Wunsch states that “ Modern sea level is a matter of urgent concern from a variety of points of view, but especially because of possibility of its acceleration and consequent threats to many low-lying parts of the inhabited world “. The Intergovernmental Panel on Climate Change (IPCC), a UN Body of scientists, has been making periodic review of the earth’s climate change since 1990. In its most recent climate change documents (Meehl 2007), the IPCC projects global sea level rise (SLR) for the next 100 years to be between 14 and 43 cm ( with a mean value of 29 cm) under an emission scenario A1B ( these emission scenarios have been developed using economic development indices for world countries) in which the earth’s mean temperature is projected to rise between 2.3C and 4.1C by 2100. The IPCC projects largest increase in SLR (about 230 mm by 2100) as due to thermal contribution, resulting from warming of the earth’s surface and associated expansion of water in future. The contribution due to melting of glaciers and ice caps is estimated by the IPCC to be about 60 mm over next 100 years. These two components namely thermal (or steric) and mass balance (or eustatic) are being closely examined at present in the context of several recent studies on climate sensitivity and observational evidence of increased glacier melting. In this chapter, a brief background of the global warming science is presented in section 2. This is followed by a discussion on sea level rise over the past several thousand years and