The first thing to note about the temperature of the Earth’s surface is that it has been variable ever since there was an atmosphere, and these variations have had no significant relationship to  the concentration of CO2 in the atmosphere.

•  Historic data show CO2 concentrations in past geological periods up to twenty times greater than the present value – without harming the climate system…. There was a period of widespread glaciation during the Ordovician (440 million years ago) when CO2 levels were fifteen times the present value. Ice core data also show climate fluctuations were much greater during the lower CO2 levels of the most recent ice age than at the higher CO2 levels of the present interglacial (Holocene) period of the last 10,000 years. Does this result suggest that higher CO2 levels promote more climate stability? (Singer, p.110).
•  Variations appear in the temperature record of the past 3,000 years as determined from ocean sediment studies in the North Atlantic … and during the past 10,000 years as shown in studies of Greenland ice cores …. [What they show are] rapid variations , as well as much warmer temperatures 1,000 and 2,500 years ago when the atmospheric CO2 concentration was only about 200 ppm (parts per million) [compared to over 400 ppm today] (Singer, p. 103).
• About 1,000 years ago, there was a world-wide MWP [Medieval Warming Period] when global temperatures were as high or higher than they were over the latter part of the twentieth century, despite there being approximately 25% less CO2 in the atmosphere than there is today (Singer, p. 91).
• Contrary to Al Gore, analysis of Antarctic ice core data show that the increase in CO2 during the recent ice age came after the temperature increase by about 600 to 800 years. Something that comes after something else can’t be its cause.
• … climate change has occurred on a scale larger than what was observed in the twentieth century, before there could have been a human role. … the … warming over the past 130 years of observational record is evidence of neither greenhouse warming nor anthropogenic (man caused) effect (Singer, p. 106).
• Since 2000, there has been little if any warming attributable to GHGs [greenhouse gases], a “pause” that is now approaching twenty years. (El Niño [warming] events in 1997-98 and 2016-2017 cannot be explained by CO2 concentrations. This means none of the extreme weather, floods, hurricanes, etc. that are so often attributed to “global warming” … could have been triggered by our GHG emissions (Singer, pp.190-191).