Climate commitment studies
Encyclopedia
Climate commitment describes the fact that climate
reacts with a delay to influencing factors ("climate forcings") such as the presence of greenhouse gas
es. Climate commitment studies attempt to assess the amount of future warming that is "committed" under the assumption of some constant level of forcings. The constant level often used for illustrative purposes is CO2
doubling or quadrupling; or the present level of forcing.
(i.e., thermal inertia) of the ocean
s.
Land only stores heat
in the top few meters.
Ocean water, by contrast, can move vertically and store heat within the ocean's depth (convection
).
This is why the land surface is observed to warm more than the oceans. It also explains the very large difference in response between
The "commitment" can apply to variables other than temperature: because of the long mixing time for heat into the deep ocean, a given surface warming commits to centuries of sea level rise from thermal expansion of the ocean. Also once a certain threshold is crossed, it is likely that a slow melting of the Greenland ice sheet will commit us to a sea level rise of 5m over millennia.
s would mount by about 10 centimetres during that time. These models do not take into account ice cap
and glacier
melting; including those climate feedback effects would give a 1°C - 1.5°C estimated temperature increase.
TAR
http://www.grida.no/climate/ipcc_tar/wg1/008.htm and in the SAR
in 1995.
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
reacts with a delay to influencing factors ("climate forcings") such as the presence of greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
es. Climate commitment studies attempt to assess the amount of future warming that is "committed" under the assumption of some constant level of forcings. The constant level often used for illustrative purposes is CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
doubling or quadrupling; or the present level of forcing.
Basic idea
If a perturbation - such as an increase in greenhouse gases or solar activity - is applied to the climate system the response will not be immediate, principally because of the large heat capacityHeat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
(i.e., thermal inertia) of the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s.
- As an analogue, consider the heating of a thin metal plate (by the sun or by a flame): the plate will warm relatively quickly. If a thick metal block is heated instead, it will take much longer for the entire block to reach equilibriumThermodynamic equilibriumIn thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium. The word equilibrium means a state of balance...
with the imposed heating because of its higher heat capacity.
Land only stores heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
in the top few meters.
Ocean water, by contrast, can move vertically and store heat within the ocean's depth (convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
).
This is why the land surface is observed to warm more than the oceans. It also explains the very large difference in response between
- "equilibrium" climate prediction runsExecution (computers)Execution in computer and software engineering is the process by which a computer or a virtual machine carries out the instructions of a computer program. The instructions in the program trigger sequences of simple actions on the executing machine...
in which only a shallow ocean is used and it is assumed that the climate has come to equilibrium and - "transient" climate prediction runs in which a full ocean is used and the climate is out of balance.
The "commitment" can apply to variables other than temperature: because of the long mixing time for heat into the deep ocean, a given surface warming commits to centuries of sea level rise from thermal expansion of the ocean. Also once a certain threshold is crossed, it is likely that a slow melting of the Greenland ice sheet will commit us to a sea level rise of 5m over millennia.
Models
Recent models forecast that even in the unlikely event of greenhouse gases stabilising at present levels, the earth would warm by an additional 0.5°C by 2100, a similar rise in temperature to that seen during the 20th century. As ocean waters expand in response to this warming, global sea levelSea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
s would mount by about 10 centimetres during that time. These models do not take into account ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....
and glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
melting; including those climate feedback effects would give a 1°C - 1.5°C estimated temperature increase.
History
This is by no means a new idea, the concept is discussed in the IPCCIntergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
TAR
Tar
Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...
http://www.grida.no/climate/ipcc_tar/wg1/008.htm and in the SAR
IPCC Second Assessment Report
The Second Assessment Report of the Intergovernmental Panel on Climate Change , published in 1996, is an assessment of the then available scientific and socio-economic information on climate change...
in 1995.
External links
- http://www.nature.com/news/2005/050314/full/050314-13.html
- GRL, VOL. 28, NO. 8, PAGES 1535–1538, 2001, Committed warming and its implications for climate change, Richard T. Wetherald et al.