how do greenhouse gases cause global warming

The Physical Mechanism

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Observed Rise in CO₂

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Quantified Warming Response

, while Hansen et al. (1988) estimated an equilibrium warming of about 4°C under CO₂ doubling in their general circulation model — a difference reflecting distinct modeling approaches. Hansen et al. (1988) also found that global surface air temperature had already risen 0.5–0.7°C over the prior century, consistent with the greenhouse effect , and projected continued warming of 0.5–1°C per decade under business-as-usual emissions .

Current Scientific Synthesis

IPCC et al. (2021) state it is "unequivocal" that human influence has warmed the atmosphere, ocean, and land, and that global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2,000 years . Each increment of warming brings increasingly severe impacts, and limiting warming to 1.5°C requires net-zero CO₂ emissions by around 2050 .

Scientific Consensus

This understanding is not fringe: Cook et al. (2016) synthesized six independent studies and found that 90–100% of publishing climate scientists share the consensus that humans are causing recent global warming, consistent with the widely cited 97% figure . The level of consensus correlates with expertise in climate science .

Note on coverage: The evidence blocks directly support the radiative mechanism, empirical CO₂ trends, modeled temperature sensitivities, and expert consensus. They do not include detail on specific gases other than CO₂ (e.g., methane, nitrous oxide), so I cannot address those from the retrieved evidence.