climate changes
Scientists are particularly concerned about “tipping points” in the earth’s systems. These involve processes in which sudden or irreversible changes occur as systems cross thresholds. Many of them operate at such a large scale that they are effectively unmanageable by humans with existing technologies. Four important global tipping points are the rapid melting of large ice sheets (such as Greenland), large- scale changes in ocean circulation such as the Gulf Stream, feedback processes where warming produces more warming, and enhanced warming over the long run. These tipping points are particularly dangerous because they are not easily reversed once they are triggered. Sea-level rise has two major components: thermal expansion and melting of terrestrial ice. Thermal expansion occurs because water density changes with different levels of temperature, salinity, and pressure. On average, as the oceans warm, they will expand, thereby raising sea level. This pa...