| gables | gables are the triangular shaped portion at the top of a wall designed to carry a sloped roof. the gable starts above the eaves and rises to a point where the ridge of the roof sits. |
| global warming | climate change resulting from greenhouse gas emissions causing significant environmental effects, such as severe weather, flooding, droughts and ice cap melts. |
| greenhouse gases | these are gases, such as carbon dioxide, which build up in the upper atmosphere and increase air temperature. this is contributing to polar ice cap melt and rising sea levels |
| greywater recycling | systems to collect, cleanse and re-use greywater can operate on a single dwelling scale or on a development-wide scale. greywater from baths, showers and hand basins is usually clean enough for flushing the toilet with only basic disinfectant or microbiological treatment. filtering the water prior to disinfecting it prevents biological activity for long enough to allow the treated water to be stored until needed. |
| green roofs | green roofs are those that are intentionally vegetated to some degree and have the potential for retain up to 90% of the rainfall within its substrate. this reduces the flow rate of rainwater, helping to reduce flooding. green roofs can vary from full blown roof gardens, through to grassy swards or sedum roofs. |
| green infrastructure | green infrastructure is the multi-functional network of green spaces which are important for recreation and well-being |
| ground source heat pumps (gshps) | gshps provide heating in the winter and in some cases cooling in the summer, using an underground loop of pipework. water is pumped through the pipes absorbing the ground heat. |
| geothermal energy | literally, the heat of the earth. where this heat occurs close to the earth's surface, and is able to maintain a temperature in the surrounding rock or water at or above 150 degrees c, it may be tapped to drive steam turbines. |
| global hectare | one hectare of biologically productive space adjusted to world average biomass productivity allowing meaningful comparisons across regions to be made. |
| global warming | an increase in the near surface temperature of the earth; global warming is most often used to refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. |
| global warming potential (gwp) | anumerical index that allows effects on global warming of various greenhouse gases to be compared, using the 100 year gwp of carbon dioxide as a reference point. carbon dioxide has a gwp of 1, methane has a gwp of 21; the gwp's of various hydrofluorocarbons range from 140 - 11,700. |
| greenbelt or greenfield | area of land often encircling a city, with extra planning restraints on development; undeveloped land. the term was first used in london in the 1940s. |
| greenfield runoff | this is the surface water runoff regime from a site before development, or the existing site conditions for brownfield redevelopment sites. |
| green roof | a roof with plants growing on its surface contributing to local biodiversity. the vegetated surface provides a degree of retention, attenuation and treatment of rainwater, and promotes evapotranspiration. |
| greenhouse effect | the roles of water vapour, carbon dioxide, and other trace gases in keeping the earth's surface warmer than it would be otherwise; they trap long wave radiation, which would otherwise escape to space, within the lower levels of the atmosphere; the subsequent reradiation of some of the energy back to the surface maintains surface temperatures higher than they would be if the gases were absent. this process occurs naturally and has kept the earth's temperature about 12oc warmer than it would otherwise be; current life on earth could not be sustained without the natural greenhouse effect. however, increased emissions of greenhouse gases may increase the surface temperature of the earth with potentially serious consequences. |
| greenhouse gases | any gas that absorbs infrared radiation in the atmosphere. greenhouse gases include water vapour, carbon dioxide (co2), methane (ch4), nitrous oxides, halogenated fluorocarbons (hcfcs), ozone (o3), perfluorinated carbons (pfcs) and hydro fluorocarbons (hfcs). |
| greenwash | to falsely claim a product is environmentally sound, or to unfoundedly bolster a product, or structures, environmental credentials. also known as faux greening. |
| greywater | water from sinks and baths that may be reused for watering, landscaping and other domestic purposes, before it reaches the sewer (or septic tank system); usually water that has been used for showering, clothes washing, and bathing. |
| groundwater | water that is below the surface of ground in the saturation zone. |