Basic Concepts

Carbon dioxide and other greenhouse gases in the atmosphere absorb and re-emit infrared radiation (heat) emitted by the Earth's surface. This process traps heat in the atmosphere, leading to the greenhouse effect and contributing to the warming of the Earth's surface temperature. Therefore, increasing levels of carbon dioxide result in the absorption of the infrared part of solar radiation, leading to the gradual warming of the atmosphere.

**Statement 1 is correct:** Volcanic action releases carbon dioxide trapped within the Earth's crust and mantle. **Statement 2 is correct:** Respiration releases carbon dioxide as a byproduct of cellular respiration in living organisms. **Statement 3 is incorrect:** Photosynthesis removes carbon dioxide from the atmosphere. Plants and other photosynthetic organisms use carbon dioxide during photosynthesis to create organic molecules.  **Statement 4 is correct:** The decay of organic matter releases carbon dioxide as decomposers break down dead plants and animals. This process returns carbon stored in organic matter back to the atmosphere as carbon dioxide.

**Statement 1 is correct:** Global warming poses a significant threat to methane hydrate deposits. These icy structures, found in permafrost and deep-sea sediments, can destabilize as temperatures rise, releasing methane into the atmosphere. Since methane is a potent greenhouse gas its release could create a positive feedback loop, further accelerating global warming. **Statement 2 is correct:** Large deposits of methane hydrate are primarily found in two locations: 1. Arctic Tundra: Permafrost soils in the Arctic hold significant methane hydrate reserves, which are at risk of melting due to rising temperatures. 2. Seafloor Deposits: Continental margins and deep ocean sediments contain vast methane hydrate reserves. Changes in ocean temperature and pressure fluctuations can trigger their release. **Statement 3 is correct:** After about 12 years, the methane is converted into carbon dioxide through hydroxyl oxidation. While CO₂ is a less potent greenhouse gas than methane, its longer atmospheric lifetime means it continues contributing to long-term climate change. Therefore, option (D) 1, 2 and 3 is correct.

Methane and nitrous oxide emissions from rice farms could have the same long-term warming impact as about 600 coal plants. Rice cultivation emits methane and nitrous oxide due to flooded fields and nitrogen-based fertilizers. Flooding creates anaerobic conditions, producing methane released through rice plants. Fertilizers poorly absorbed by rice lead to soil microbes converting nitrogen into nitrous oxide.

**Statement 1 is incorrect.** Insolation reaches the earth's surface in short waves and heat is radiated from the earth in long waves, Hence energy leaving the earth's surface i.e. terrestrial radiation heats up the atmosphere more than the incoming solar radiation i.e. insolation.  **Statement 2 is correct.** Greenhouse gases in the atmosphere (such as water vapour and carbon dioxide) absorb most of the Earth's emitted longwave infrared radiation, which heats the lower atmosphere.