What caused the apparently massive temperature leap at the beginning of the 18^th Century? It certainly wasn't industrialization, that hadn't happened yet. If such changes appear in the record during recent periods when people can not have caused them then they are by definition "natural" and, if such natural changes are evident in recent history, why are we so fixated on carbon dioxide as a "culprit" driving lesser warming now?

Finally, it is worth wondering why, with some three and one-half centuries of population growth, development and urbanization depicted in the Central England Temperature series, recent "chart-toppers" have managed to elevate top temperatures by a paltry 0.16 °C over those of the early 1730s. The vast majority of increase in atmospheric carbon dioxide has taken place over the seventy years since the Second World War and if CO₂ were a significant driver of temperature change we would expect those years to be almost exclusively represented in the highest temperatures and yet fewer than half manage to make the warmest one-hundred list. The post hoc ergo propter hoc association of carbon dioxide is observed to increase, warmer temperatures are measured, therefore carbon dioxide warms the planet is a very poor basis for the current fixation.

What are the take-home messages:

The temperature effect of atmospheric carbon dioxide is logarithmic, not exponential.

The potential planetary warming from a doubling of atmospheric carbon dioxide from pre-Industrial Revolution levels of ~280ppmv to 560ppmv (possible some time later this century - perhaps) is generally estimated at less than 1 °C.

The guesses of significantly larger warming are dependent on "feedback" (supplementary) mechanisms programmed into climate models. The existence of these "feedback" mechanisms is uncertain and the cumulative sign of which is unknown (they may add to warming from increased atmospheric carbon dioxide or, equally likely, might suppress it).

The total warming since measurements have been attempted is thought to be about 0.6 degrees Centigrade. At least half of the estimated temperature increment occurred before 1950, prior to significant change in atmospheric carbon dioxide levels. Assuming the unlikely case that all the natural drivers of planetary temperature change ceased to operate at the time of measured atmospheric change then a 30% increment in atmospheric carbon dioxide caused about one-third of one degree temperature increment since and thus provides empirical support for less than one degree increment due to a doubling of atmospheric carbon dioxide.  (EA)

There is no linear relationship between atmospheric carbon dioxide change and global mean temperature or global mean temperature trend -- global mean temperature has both risen and fallen during the period atmospheric carbon dioxide has been rising.

Despite attempts to label atmospheric carbon dioxide a "pollutant" it is, in fact, an essential trace gas, the increasing abundance of which is a bonus for the bulk of the biosphere.

There is no reason to believe that slightly lower temperatures are somehow preferable to slightly higher temperatures - there is no known "optimal" nor any known means of knowingly and predictably adjusting some sort of planetary thermostat.