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GPT-5Oct 3, 2026openai/gpt-5-2025-08-07
Are humans responsible for climate change?
Yes. Humans are the dominant cause of the rapid warming observed since the mid‑20th century.
Why scientists are confident:
•Greenhouse gases: CO2, methane, and nitrous oxide have surged due mainly to burning fossil fuels, deforestation, and cement production. CO2 has risen from ~280 ppm before 1850 to over 420 ppm today—levels not seen for millions of years.
•Fingerprints: The pattern of change matches greenhouse warming, not natural cycles—troposphere warming with stratosphere cooling, nights warming faster than days, winters warming faster than summers, and strongest warming in the Arctic.
•Isotopes and oxygen: The carbon in the extra CO2 has a fossil‑fuel isotopic signature, and atmospheric oxygen is declining as expected from combustion.
•Energy balance and oceans: Satellites and ocean measurements show Earth is gaining heat; over 90% of it is accumulating in the oceans.
•Attribution studies: When human emissions are included, climate models reproduce observed warming; using only natural factors (solar variability, volcanoes) does not.
Bottom line: Natural influences alone would have caused little change or slight cooling over recent decades; human activities account for essentially all of the observed warming. If you’d like, I can share accessible sources or dig into any of these lines of evidence in more detail.