How do human activities impact the carbon cycle and climate feedbacks?

• A. Emissions raise atmospheric CO2, intensifying warming; feedbacks include vegetation changes, cloud properties, permafrost thaw.
• B. Emissions lower CO2 causing cooling.
• C. No impact.
• D. Feedbacks always dampen warming.

Answer: (A)

Human activities change the amount of CO2 in the atmosphere, and CO2 is a greenhouse gas that traps heat. So when emissions from burning fossil fuels and other sources raise atmospheric CO2, the Earth warms more than it otherwise would. The climate system then responds with feedbacks that can amplify this warming. Vegetation changes can alter how much carbon ecosystems store or release, and warming can shift plant communities or soil respiration in ways that release more carbon. Cloud properties—such as how they form, their altitude and reflectivity—change how much solar energy reaches the surface and how much heat escapes to space, affecting the energy balance in ways that can strengthen or partly counteract warming. Thawing permafrost releases large amounts of methane and CO2 from previously frozen soils, adding more greenhouse gases to the atmosphere and pushing warming further.

The other options don’t fit because emissions don’t cool the planet, there is a clear impact from human activities, and climate feedbacks are not limited to damping warming; several positive feedbacks in the examples above tend to enhance the warming rather than suppress it.