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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.
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]
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects of a small disturbance.
A consequence of global warming, feedback loops are already making a huge problem that much worse. 'It's already begun': Feedback loops will make climate change even worse, scientists say [Video ...
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.
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 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.
Scientists subsequently tested the hypothesis. Some concluded that there was no evidence supporting the hypothesis. [3] Others found evidence suggesting that increased sea surface temperature (SST) in the tropics did indeed reduce cirrus clouds but found that the effect was nonetheless a positive climate feedback rather than the negative feedback that Lindzen had hypothesized.