Early 20th century global warming climate change greater during a low atmospheric CO2 environment.
The CO2-centric global warming "theory" has serious issues, including:
==> 1. it can't be proven in the real world, it's simply not verifiable
==> 2. climate models using this theory as a foundational element have proven to be unreliable
==> 3. it can't account for the the wide variation in temperature levels and changes across the globe, whether the period is short-term or long-term.
And that's not even considering all the failed catastrophic predictions that the "theory" inspires in abundance, yet never seem to come about.
In regards to bullet point #3 above, two prior posts (here and here) provide the indisputable empirical evidence that CO2 growth has not produced a constant, runaway global warming acceleration - not even close.
Then there is the salient point that the September 2017 average monthly global temperature is similar to some observed during the 1997-99 period, as noted in this article.
Clearly, CO2 is not the powerful accelerant, nor determinant, that is going to overwhelm natural warming and cooling cycles as hypothesized.
Which leads to another observation about natural global warming and climate change: past empirical evidence from earlier in the 20th century confirms that Earth's natural climate oscillations can produce periods of significant temperature change increases that even exceed the most recent temperature climate change.
Case in point: September 1944 versus September 2017, as seen on the adjacent chart.
Certainly, there is no disagreement that in 1944 the atmospheric levels of CO2 were significantly lower (311 ppm) than now (407 ppm). The amount of yearly CO2 emissions per year prior to 1944 were a fraction of today's consumer/industrial annual production of emission tonnes.
Yet the earlier global temperature changes exceed the September 2017 measurements.
For example, as the chart depicts for the 240-month (20-yr) period ending September 2017, the global temperature change was +0.08°C. In other words, after 20 years of massive CO2 emissions that's all the global warming that took place.
In contrast, the 240-month (20-Yr) period ending September 1944 was a +0.58°C global temperature change - substantially greater than recent warming.
That +0.58°C warming over the earlier 20-year period was produced by natural climate change drivers, not CO2 emissions.
As the chart reveals, every single medium and long-term period ending at September 1944 had global warming changes that exceeded their respective spans ending in September 2017. (Although not shown on the chart, this was also true for the short-term periods of 1-Yr, 2-Yr, and 3-Yr.)
And, there are other earlier extended periods prior to the 1960's, where global temperature warming change is greater than relevant recent periods.
The science is settled?
Not very likely, since it is without question that this and other climate science empirical evidence does not support, nor validate, the foundational Arrhenius greenhouse global warming theory that dominates the consensus orthodoxy.
Simply stated, it's a dog theory that has gone dogmatic without a bone of evidence. And another admission to a collection of 'those stubborn facts.'
Prior global temperature charts.
Note: Source of HadCRUT global temperature data. Excel was used to calculate/chart for the various periods of temperature change based on month endpoints of September 1944 and September 2017.