Carbon dioxide is one of the major greenhouse gases. The SRES contains "scenarios" of future changes in emissions of greenhouse gases and sulfur dioxide. Two inert gases or gas mixtures are employed. This is analogous to the greenhouse effect of greenhouse gases and water vapor. Water vapor responds to and amplifies effects of the other greenhouse gases. This generally involves reductions in human emissions of greenhouse gases (GHGs). Electricity generation emits over a quarter of global greenhouse gases. Sulfur forms stable compounds with all elements except the noble gases. Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. This beneficially masks some of the warming caused by increased greenhouse gases. Welders are often exposed to dangerous gases and particulate matter. This is caused by the emission of sulphurous gases. Furthermore, it is highly reactive and interacts with other greenhouse gases and aerosols. It is also somewhat permeable to highly volatile gases and liquids. A pressure sensor is a device for pressure measurement of gases or liquids.