Sea level is affected by changes in the density of sea water, induced by temperature changes (thermosteric) or by salinity changes (halosteric). Each section begins with a summary of findings from the IPCC Fourth Assessment Report, then evaluates more recent results. This chapter evaluates the contributions of thermal expansion, glaciers, ice sheets, and other terrestrial sources of water to global sea-level rise. In the most recent estimate, for 1993–2008, the contribution from land ice increased to 68 percent, the contribution from thermal expansion decreased to 35 percent, and land water storage contributed -3 percent (sea-level fall Church et al., 2011). Subsequent work has corrected instrument biases, reducing estimates of the thermal expansion contribution to sea-level rise, and recorded increased rates of land ice loss. The improved agreement between estimates of the individual contributions and the total sea-level rise for the later time period was attributed to the availability of satellite altimetry data and other global ocean data sets and to better knowledge of the processes causing sea-level rise. For the last 10 years of that period (1993–2003), the IPCC estimated that thermal expansion and land ice melt each contributed about half to the total sea-level rise. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report found that thermal expansion accounted for about one-quarter of the observed sea-level rise for 1961–2003, melting of land ice accounted for less than half, and changes in land water storage accounted for less than 10 percent (Bindoff et al., 2007). Sea-level rise is governed by processes that alter the volume of water in the global ocean-primarily thermal expansion of sea water and transfers of water from terrestrial reservoirs, such as land ice and groundwater, to the ocean.
0 kommentar(er)
