Question

What are greenhouse gasses? How does carbon dioxide enter the atmosphere? (Site 1)

Answer 1

Short answer
- Greenhouse gases are atmospheric gases that let sunlight in but absorb and re‑emit the earth’s outgoing infrared (heat) radiation, warming the planet (the “greenhouse effect”).
- Carbon dioxide (CO2) enters the atmosphere from both natural processes (respiration, decomposition, volcanic release, ocean‑air exchange, wildfires, permafrost thaw) and human activities (burning fossil fuels, cement production, deforestation/land‑use change, biomass burning).

More detail
- Examples of greenhouse gases: water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and manufactured gases like CFCs. Different gases vary in how long they stay in the atmosphere and how strongly they trap heat.
- Natural CO2 sources:
- Respiration by plants, animals, microbes (breaks down organic carbon and returns CO2 to the air).
- Decomposition and wildfires that release stored carbon.
- Volcanic eruptions and geothermal activity.
- Exchange with the oceans (warmer water releases CO2; colder water absorbs it).
- Thawing permafrost and peatlands can release previously frozen carbon.
- Human (anthropogenic) CO2 sources:
- Burning fossil fuels (coal, oil, natural gas) for electricity, transport, heating and industry — the largest human source.
- Cement and concrete production (chemical release of CO2 when limestone is converted to clinker).
- Deforestation and land‑use change: clearing or burning vegetation reduces carbon storage and releases CO2.
- Large‑scale biomass burning and some industrial processes.
- Why human CO2 matters: added CO2 increases the atmospheric greenhouse gas concentration, enhancing the greenhouse effect and driving global temperature rise. Atmospheric CO2 has risen substantially since the pre‑industrial era due mainly to fossil fuel use and land‑use change.

Site 1 (general source)
- NASA — Climate: Causes (greenhouse gases and CO2 sources): https://climate.nasa.gov/causes/