The IPCC’s fifth assessment report, published more than a century after Arrhenius offered the value of 4°C, concluded that it is extremely unlikely that the sensitivity is less than 1°C and very unlikely that it is above 6°C, with the likely range between 1.5°C and 4.5°C, the same as the 1979 National Research Council report.[50] And in 2019, a comprehensive assessment of Earth’s climate sensitivity (using multiple lines of evidence) narrowed the most likely response to between 2.6°C and 3.9°C.[51] This means that climate sensitivity is extremely unlikely to be so low that it could prevent
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