Climate change is driven by factors that alter Earth’s energy balance (the amount of solar energy the planet absorbs vs. the amount it emits to space). The recent warming observed over the past century — and especially since the mid-20th century — is primarily caused by human activities. Key reasons are:

1. Increased greenhouse gases (main driver)
- Burning fossil fuels (coal, oil, gas) for electricity, heat, transport and industry releases large amounts of carbon dioxide (CO2).
- Deforestation and some land-use changes reduce the planet’s ability to absorb CO2 and release stored carbon.
- Agriculture, waste, and some industrial processes emit methane (CH4) and nitrous oxide (N2O).
- These gases absorb and re-emit infrared (heat) radiation in the atmosphere (the greenhouse effect), trapping heat and raising Earth’s average temperature. Atmospheric CO2 has risen from about 280 ppm before the Industrial Revolution to roughly 420+ ppm today — a substantial increase that changes the planet’s radiative balance.

2. Land-use changes
- Converting forests and wetlands to agriculture or urban areas changes surface reflectivity (albedo), local evaporation, and carbon storage — contributing to warming in many regions.

3. Aerosols and particulate effects (complex)
- Human-made aerosols (tiny particles from fossil-fuel combustion, biomass burning, industry) can reflect sunlight and cool the surface, or absorb heat and warm the atmosphere, depending on their type. Overall, aerosols have partly offset (masked) some greenhouse-gas warming but also have harmful health effects.
- Aerosols also affect clouds (their brightness and lifetime), with further climate impacts that are complex and regional.

4. Feedback mechanisms (amplifying or damping effects)
- Water vapor feedback: warming increases atmospheric water vapor (a potent greenhouse gas), which in turn causes more warming.
- Ice–albedo feedback: melting snow and ice expose darker surfaces (ocean, land), which absorb more sunlight and lead to further warming.
- Permafrost thaw releases CO2 and methane, potentially amplifying warming.

5. Natural factors (smaller role in recent warming)
- Solar variability (changes in solar output) and volcanic eruptions affect climate. Large volcanic eruptions inject reflective particles into the stratosphere and cause short-term cooling.
- Natural internal variability (e.g., El Niño / La Niña cycles, ocean circulation changes) causes year-to-decade fluctuations.
- While these natural factors influence climate, they cannot account for the long-term global warming trend seen since the mid-20th century. Multiple lines of evidence (direct measurements, climate models, and isotope studies) attribute the majority of recent warming to human greenhouse-gas emissions.

In short: human-driven increases in greenhouse gases are the dominant cause of the current climate change, with land-use change, aerosols, and various natural processes and feedbacks modulating the magnitude and regional patterns of warming.
