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GPT-5Sep 9, 2026openai/gpt-5-2025-08-07
Are humans responsible for climate change?
Yes
Yes. Human activities are the dominant cause of the warming observed since the mid-20th century.
Key evidence:
•Greenhouse gases: CO2 has risen about 50% since preindustrial times and methane has more than doubled, primarily from burning fossil fuels, deforestation, and industry. Their heat-trapping effect is well measured.
•Fingerprints: The pattern of change matches greenhouse warming—troposphere warms while the stratosphere cools, nights and winters warm faster than days and summers, the Arctic warms faster than the globe, oceans gain vast amounts of heat, and sea ice and glaciers retreat.
•Carbon source tracing: The declining 13C/12C ratio and small drop in atmospheric O2 show the added CO2 comes from fossil fuels; oceans are acidifying as they absorb it.
•Attribution studies: Only models that include human emissions reproduce the observed warming; natural factors (solar changes, volcanoes) cannot explain the trend. Best estimates attribute essentially all net warming since 1950 to human influence.
•Context: The rate and scale of recent warming are unprecedented for at least 2,000 years; CO2 levels are the highest in over 2 million years.
This conclusion reflects the consensus of the IPCC and national science academies worldwide.