Explain “Cloud feedback” and “Lapse-rate feedback”.

"Cloud feedback" and "lapse-rate feedback" are two important mechanisms in the Earth's climate system that can either amplify or dampen the effects of external climate forcings, such as greenhouse gas emissions, on global temperatures. Understanding these feedback processes is crucial for predicting future climate change and assessing the sensitivity of the climate system to external perturbations.

1. Cloud Feedback:
   Clouds play a significant role in the Earth's climate system, acting as both a source of cooling and warming depending on their altitude, composition, and coverage. Cloud feedback refers to the amplification or dampening of climate change caused by changes in cloud properties in response to external climate forcings.

Positive Cloud Feedback: When the climate warms due to increased greenhouse gas concentrations or other factors, it can lead to changes in cloud cover, altitude, and properties. In some cases, warming can enhance the formation of low-level clouds, such as stratocumulus, which have a net cooling effect on the Earth's surface by reflecting incoming solar radiation back into space (albedo effect). However, as the climate warms further, these low-level clouds may become thinner or dissipate, reducing their reflective properties and allowing more sunlight to reach the Earth's surface, thus amplifying warming (positive feedback).

Negative Cloud Feedback: Conversely, changes in atmospheric circulation, moisture content, and cloud distribution can also lead to the formation of high-altitude clouds, such as cirrus clouds, which trap outgoing longwave radiation emitted by the Earth's surface, thus enhancing the greenhouse effect and warming the climate (positive feedback). However, high-altitude clouds can also have a net cooling effect by reflecting incoming solar radiation and enhancing outgoing longwave radiation, particularly at night, thus dampening warming (negative feedback).

The net effect of cloud feedback on climate sensitivity remains uncertain and is a subject of ongoing research. Climate models incorporate various representations of cloud processes and feedbacks to simulate future climate scenarios and assess the likelihood of different outcomes.

1. Lapse-Rate Feedback:
   The lapse rate refers to the rate at which air temperature decreases with increasing altitude in the Earth's atmosphere. The lapse-rate feedback refers to the amplification or dampening of climate change caused by changes in the vertical temperature profile of the atmosphere in response to external climate forcings.

Positive Lapse-Rate Feedback: When the climate warms due to increased greenhouse gas concentrations, the rate of temperature decrease with altitude (lapse rate) may change. In a warmer climate, the troposphere (lower atmosphere) tends to expand, leading to a decrease in the lapse rate. A reduced lapse rate enhances the greenhouse effect by reducing the rate at which heat escapes to space, thus amplifying warming (positive feedback).

Negative Lapse-Rate Feedback: Conversely, in a cooler climate, the troposphere contracts, leading to an increase in the lapse rate. An increased lapse rate enhances the rate of heat loss to space, thus dampening warming (negative feedback). Additionally, changes in atmospheric circulation patterns and cloud cover can also influence the vertical temperature profile of the atmosphere and contribute to lapse-rate feedbacks.

The net effect of lapse-rate feedback on climate sensitivity depends on various factors, including atmospheric composition, circulation patterns, and cloud dynamics. Climate models incorporate representations of lapse-rate feedback to simulate future climate scenarios and assess the relative importance of different feedback mechanisms.

In summary, cloud feedback and lapse-rate feedback are important climate feedback mechanisms that can either amplify or dampen the effects of external climate forcings on global temperatures. Understanding these feedback processes is essential for improving climate models, predicting future climate change, and informing climate mitigation and adaptation strategies.