Charted: How we know humans cause global warming
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In addition to the myriad physical science indicators, such as glaciers around the world melting synchronously, one of the ways we know that modern climate change is human-caused is by looking at temperature observations and comparing them with what would be expected if only natural variability were at work.
Why it matters: This approach to analyzing climate change causation has been tested and retested by scientists over the past decades, each time resulting in the same answer.
How it works: Scientists from the Intergovernmental Panel on Climate Change plotted global average temperatures going back to 1850 and compared these trends with computer models simulating what would be expected from natural variability alone.
- Only the models that incorporate both human influences — mainly the increase in greenhouse gas emissions — and natural factors, such as volcanic eruptions and changes in solar output, match the observed record.
Go deeper: IPCC's journey from "probable" to "unequivocal" on human-caused warming
