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GPT-5Sep 28, 2026openai/gpt-5-2025-08-07
Are humans responsible for climate change?
Short answer: Yes. Humans are the primary cause of recent global warming.
Why scientists are confident:
•Observed changes match greenhouse-gas physics: CO2, methane, and nitrous oxide trap heat. CO2 has risen from ~280 ppm pre‑industrial to over 420 ppm today, mainly from burning fossil fuels and deforestation.
•Clear human “fingerprints”:
•Fossil‑fuel carbon isotopes show up in the atmosphere.
•Atmospheric oxygen is declining as carbon is burned.
•The lower atmosphere warms while the stratosphere cools (a greenhouse signature, not solar).
•Nights and winters warm faster than days and summers; oceans are accumulating vast amounts of heat.
•Natural factors can’t explain the trend: Solar output changes and volcanic activity would have produced little warming (or slight cooling) over recent decades; internal variability can’t generate the persistent, global, multi‑decadal warming observed.
•Multiple independent lines of evidence and models agree: Only when human emissions are included do climate models reproduce the magnitude and pattern of warming since the mid‑20th century.
In sum, the best estimate is that human activities account for essentially all of the net warming observed since the late 1800s.