Which is a positive climate feedback?

Which is a positive climate feedback?

• A. Planck feedback via increased infrared emission with warming
• B. Vegetation evapotranspiration cooling
• C. Cloud albedo feedback always cools the planet
• D. Water vapor feedback amplifies warming

Answer: (D)

Water vapor feedback amplifies warming. When air temperatures rise, the atmosphere can hold more water vapor. Water vapor is a powerful greenhouse gas, so higher concentrations trap more outgoing infrared radiation and warm the surface further. This creates a reinforcing loop: warming boosts water vapor, which in turn causes more warming. That makes it a positive feedback. Planck feedback is a negative response—warmer air emits more infrared radiation to space, which tends to cool the planet. Cloud albedo feedback isn’t fixed; clouds can either cool or warm depending on their properties and height, so the statement that it always cools isn’t accurate. Vegetation evapotranspiration cooling acts to reduce surface warming, so it’s also a negative feedback.

Water vapor feedback amplifies warming.

When air temperatures rise, the atmosphere can hold more water vapor. Water vapor is a powerful greenhouse gas, so higher concentrations trap more outgoing infrared radiation and warm the surface further. This creates a reinforcing loop: warming boosts water vapor, which in turn causes more warming. That makes it a positive feedback.

Planck feedback is a negative response—warmer air emits more infrared radiation to space, which tends to cool the planet. Cloud albedo feedback isn’t fixed; clouds can either cool or warm depending on their properties and height, so the statement that it always cools isn’t accurate. Vegetation evapotranspiration cooling acts to reduce surface warming, so it’s also a negative feedback.