New research shows evidence that the CO2 sensitivity of Earth’s climate system may in fact increase with warming. During the PETM, when temperatures rose by 5-8 degrees in about 10,000 years CO2 climate sensitivity rose from 3.3–5.6 to 3.7–6.5, values much higher than today’s most cited numbers.

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New research shows evidence that the CO2 sensitivity of Earth’s climate system may in fact increase with warming. During the PETM, when temperatures rose by 5-8 degrees in about 10,000 years CO2 climate sensitivity rose from 3.3–5.6 to 3.7–6.5, values much higher than today’s most cited numbers.