The IPCC 5th Assessment Report (AR5) from 2013 shows the range of results that climate models produce for global warming. These are under a set of conditions which for simplicity is doubling CO2 in the atmosphere from pre-industrial levels. The 2xCO2 result. Also known as ECS or equilibrium climate sensitivity.
The range is about 2-4ºC. That is, different models produce different results.
Other lines of research have tried to assess the past from observations. Over the last 200 years we have some knowledge of changes in CO2 and other “greenhouse” gases, along with changes in aerosols (these usually cool the climate). We also have some knowledge of how the surface temperature has changed and how the oceans have warmed. From this data we can calculate ECS.
This comes out at around 1.5-2ºC.
Some people think there is a conflict, others think that it’s just the low end of the model…
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