What+are+the+environmental+effects+of+climate+change?


 * What are the environmental consequences of climate change?

Key ideas: 1. Extreme weather (flooding, drought) 2. Crop yields, species extinction 3. Sea level rise 4. Artic shrinkage, glacial retreat

** Water cycles between [|ocean], [|atmosphere], and [|glaciers]. Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by [|waves] and [|tides] are smoothed out. One must adjust perceived changes in LMSL to account for vertical movements of the land, which can be of the same order (mm/yr) as sea level changes. Some land movements occur because of [|isostatic] adjustment of the [|mantle] to the melting of [|ice sheets] at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the [|land slowly rebounds]. [|Atmospheric pressure], [|ocean currents] and local ocean [|temperature] changes also can affect LMSL. “[|Eustatic]” change (as opposed to local change) results in an alteration to the global sea levels, such as changes in the volume of water in the world oceans or changes in the volume of an [|ocean basin]. 

[[|edit]] Short term and periodic changes
There are many factors which can produce short-term (a few minutes to 14 months) changes in sea level. (P = period) ||~ Vertical effect || 
 * ~ Short-term (periodic) causes ||~ Time scale
 * ~ Periodic sea level changes ||
 * Diurnal and semidiurnal astronomical tides || 12–24 h P || 0.2–10+ m ||
 * Long-period tides ||  ||   ||
 * Rotational variations ([|Chandler wobble]) || 14 month P ||
 * ~ Meteorological and oceanographic fluctuations ||
 * Atmospheric pressure || Hours to months || –0.7 to 1.3 m ||
 * Winds ([|storm surges]) || 1–5 days || Up to 5 m ||
 * [|Evaporation] and [|precipitation] (may also follow long-term pattern) || Days to weeks ||  ||
 * Ocean surface [|topography] (changes in water [|density] and currents) || Days to weeks || Up to 1 m ||
 * [|El Niño]/[|southern oscillation] || 6 mo every 5–10 yr || Up to 0.6 m ||
 * ~ Seasonal variations ||
 * [|Seasonal] water balance among oceans (Atlantic, Pacific, Indian) ||  ||   ||
 * Seasonal variations in slope of water surface ||  ||   ||
 * [|River] runoff/[|floods] || 2 months || 1 m ||
 * Seasonal water density changes (temperature and [|salinity]) || 6 months || 0.2 m ||
 * ~ Seiches ||
 * [|Seiches] (standing waves) || Minutes to hours || Up to 2 m ||
 * ~ [|Earthquakes] ||
 * [|Tsunamis] (generate catastrophic long-period waves) || Hours || Up to 10 m ||
 * Abrupt change in land level || Minutes || Up to 10 m ||

[[|edit]] Longer term changes
Various factors affect the volume or mass of the ocean, leading to long-term changes in eustatic sea level. The two primary influences are temperature (because the volume of [|water] depends on temperature), and the [|mass] of water locked up on land and sea as [|fresh water] in rivers, [|lakes], glaciers, [|polar ice caps], and [|sea ice]. Over much longer [|geological timescales], changes in the shape of the oceanic basins and in land/sea distribution will affect sea level. Observational and modelling studies of [|mass loss from glaciers and ice caps] indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 18th century. 

[[|edit]] Glaciers and ice caps
Each year about 8 mm (0.3 inch) of water from the entire surface of the oceans falls into the [|Antarctica] and [|Greenland] ice sheets as [|snowfall]. If no ice returned to the oceans, sea level would drop 8 mm every year. To a first approximation, the same amount of water appeared to return to the ocean in [|icebergs] and from ice melting at the edges. Scientists previously had estimated which is greater, ice going in or coming out, called the **[|mass balance]**, important because it causes changes in global sea level. High-precision [|gravimetry] from [|satellites] in low-noise flight has since determined Greenland is losing millions of tons per year, in accordance with loss estimates from ground measurement. [|Ice shelves] float on the surface of the sea and, if they melt, to first order they do not change sea level. Likewise, the melting of the [|northern polar] [|ice cap] which is composed of floating [|pack ice] would not significantly contribute to rising sea levels. Because they are fresh, however, their melting would cause a very small increase in sea levels, so small that it is generally neglected. It can however be argued that if ice shelves melt it is a precursor to the melting of ice sheets on Greenland and Antarctica [//[|citation needed]//]. The current rise in sea level observed from tide gauges, of about 1.8 mm/yr, is within the estimate range from the combination of factors above[|[4]] but active research continues in this field. The terrestrial storage term, thought to be highly uncertain, is no longer positive, and shown to be quite large.
 * Scientists previously lacked knowledge of changes in terrestrial storage of water. Surveying of water retention by soil absorption and by reservoirs outright ("impoundment") at just under the volume of [|Lake Superior] agreed with a dam-building peak in the 1930s-1970s timespan. Such impoundment masked tens of millimeters of sea level rise in that span. (//Impact of Artificial Reservoir Water Impoundment on Global Sea Level//  B. F. Chao,* Y. H. Wu, Y. S. Li).
 * If small [|glaciers] and [|polar] ice caps on the margins of Greenland and the [|Antarctic Peninsula] melt, the projected rise in sea level will be around 0.5 m. Melting of the [|Greenland ice sheet] would produce 7.2 m of sea-level rise, and melting of the [|Antarctic ice sheet] would produce 61.1 m of sea level rise.[|[2]] The collapse of the grounded interior reservoir of the [|West Antarctic Ice Sheet] would raise sea level by 5-6 m.[|[3]]
 * The [|snowline] altitude is the [|altitude] of the lowest [|elevation] interval in which minimum annual snow cover exceeds 50%. This ranges from about 5,500 metres above sea-level at the equator down to sea level at about 70° N&S [|latitude], depending on regional temperature amelioration effects. [|Permafrost] then appears at sea level and extends deeper below sea level polewards.
 * As most of the Greenland and Antarctic ice sheets lie above the snowline and/or base of the permafrost zone, they cannot melt in a timeframe much less than several [|millennia]; therefore it is likely that they will not, through melting, contribute significantly to sea level rise in the coming century. They can, however, do so through acceleration in flow and enhanced iceberg calving.
 * [|Climate changes] during the 20th century are estimated from modelling studies to have led to contributions of between –0.2 and 0.0 mm/yr from Antarctica (the results of increasing precipitation) and 0.0 to 0.1 mm/yr from Greenland (from changes in both precipitation and [|runoff]).
 * Estimates suggest that Greenland and Antarctica have contributed 0.0 to 0.5 mm/yr over the 20th century as a result of long-term adjustment to the end of the last ice age.