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The initial change that triggers a feedback may be externally forced, or may arise through the climate system's internal variability. [2]: 2222 External forcing refers to "a forcing agent outside the climate system causing a change in the climate system" [2]: 2229 that may push the climate system in the direction of warming or cooling.
A positive feedback loop speeds up a process. Meadows indicates that in most cases, it is preferable to slow down a positive loop, rather than speeding up a negative one. The eutrophication of a lake is a typical feedback loop that goes wild. In a eutrophic lake (which means well-nourished), much life, including fish, can be supported.
Positive climate change feedbacks amplify changes in the climate system, and can lead to destabilizing effects for the climate. [2] An increase in temperature from greenhouse gases leading to increased water vapor (which is itself a greenhouse gas) causing further warming is a positive feedback, but not a runaway effect, on Earth. [13]
This is known as the ecosystem perspective. This perspective requires a change in environmental parameters that affect the behavior of state variables. For example, birth rate, death rate, migration, and density-dependent predation indirectly alter the ecosystem state by changing population density (a state variable). Ecosystem parameters are ...
In this case, a negative feedback loop creates stability. The lower equilibrium point for the constant harvest level H 1 {\displaystyle H_{1}} is not stable however; a population crash or illegal harvesting will decrease population yield farther below the current harvest level, creating a positive feedback loop leading to extinction.
Climate sensitivity is the change in surface air temperature per unit change in radiative forcing, and the climate sensitivity parameter [note 3] is therefore expressed in units of °C/(W/m 2). Climate sensitivity is approximately the same whatever the reason for the radiative forcing (such as from greenhouse gases or solar variation ). [ 26 ]
In May 2000 the Global Environment Facility approved a $7 million grant, followed in July 2000 by a United Nations Foundation $4 million grant and financial support from the government of Norway for the first meeting of the Board of the MA in Trondheim, and in December 2000 a $2.4 million grant by the Packard Foundation for a total of more than $13.4 million, considered "75% of the full budget".
Radiative forcing is defined in the IPCC Sixth Assessment Report as follows: "The change in the net, downward minus upward, radiative flux (expressed in W/m 2) due to a change in an external driver of climate change, such as a change in the concentration of carbon dioxide (CO 2), the concentration of volcanic aerosols or the output of the Sun." [3]: 2245