Climate response and climate feedbacks
Changes in any of the components of the climate system will result in climate variations. For example the EL Nino _Southern Oscillation (ENSO) which is a result of the coupled interactions between the atmosphere and ocean waters.
These are of significance in climate variability since ENSO influence vanishes from the mean statistical values.
Climate feedback; A climate feedback can be described as a process taking place in any of the components of the climate system, whose effect would be to amplify or reduce the initial process. Those that amplify are called positive feedbacks and those that reduce are negative feedbacks
Feedback mechanism Ahrens (2000); This is a process whereby an initial change in an anthropogenic process will tend to either reinforce the process
(positive feedback) or weaken the process (negative feedback).
Feedbacks complicate the response of a climate forcing. Some feedbacks amplify the original warming (positive feedback) while others reduce it
(negative feedback).
Examples of climate feedback
1. Water vapour feedback: (a) Water vapour increases when the atmosphere warms up (Positive feedback) (b) Increase in water vapour will amplify the warming (positive feedback).
2. Ice-albedo feedback; Decrease of ice with high albedo in the high latitude will decrease the reflected isolation( positive feedback). On the other hand increased open water spaces may lead to more water vapour, fog and low clouds offsetting the change in surface albedo.
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3 The thermostat Hypothesis by Ramanathan and Collin(1991)
The THERMOSTAT Hypothesis By Ramanathan and Collin( 1994)
+ve feedback
Surface
Evaporatio n
Strong
Convection
+ve feedback +ve
SST
--ve feedback
Bright high clouds
( 1) An external source of energy (sun) perturbation leads to increases in the Sea
Surface Temperatures(+ve feedback). ( 2)Then the increased SST promotes stronger evaporation ( +ve feedback). (3) The stronger evaporation promotes stronger convection (+ve feedback). (4) The vigorous convection promotes
High bright clouds (+ve feedback). (5) The high bright clouds which are usually thick have a very high albedo (around 80%) just like snow surface. This will reflect most of the incoming solar radiation back to space resulting in the cooling or reduced Sea Surface Temperatures (SST). This is how the earths manages to maintain a fairly constant mean temperature of around 15s deg
Celcius . This works just like a thermostat hence called the Themostat
Hypothesis. The warming at some point triggers a reverse mechanism which is the cooling due to the bright high Clouds.
This works as a self regulating system and can be used to explain why the global mean temperatures are fairly constant at 15 deg Celcius. The climate system works with this regulatory mechanism to maintain a radiation balance.
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There are a number of feedbacks that one can talk about especially relating to the carbon cycle. The behaviour of ecosystems and other biogeochemical processes greatly influence climate change.
Much remains to be learned about these feedbackcs and their influence on predictions of future carbon dioxide concentration and climate. Currently models for climate change do not incorporate the effects of most feedbacks like cloud cover and water vapour.
The Role Of Oceans
Oceans cover about 70 % of the earth’s surface .
● High heat capacity
● high diversity of ecosystems
●Wind stress at sea-surface drive ocean currents
● Water Vapour provides latent heat to the atmosphere
● Ocean currents provide an effective way of heat redistribution and fresh water around the globe
● Oceans are a major heat storage facility for the earth
● Carbon dioxide Sink : Ocean currents are a major sink for the global Carbon dioxide.
The Role of Land and Land masses
Over the land heat can only penetrate 2 meters into the ground hence the land masses have a small heat capacity
● Land masses play a smaller role in heat storage
● Larger diurnal, seasonal and annual temperature ranges exist over land masses ie centre of large continents eg Asia, America
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●Topographical features: The land has a variety of topographical features which can influence and modify climate
● Terrestrial Biomes: A Multiplicity of ecosystems exist over terrestrial biomes eg , Types of vegetation. These normally have some footprint on the climate.
NB many of the terrestrial features cannot be modelled in climate change prediction models
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