Last updated by The POOG on July 25,2021.

CO2 is the key issue surrounding the anthropomorphic global warming (AGW) hysteria. In this article we explore characteristics of the gas and its relation to climate.

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Historical CO2 Data

A long-term historical record of CO2 concentration in the atmosphere extending back 40 million years was created by Pagani et al. (2005). Anthony Watts provided the following chart, Figure 1a, from the paper. Unfortunately the authors did not provide a vertical scale but I’ve seen estimates that atmospheric CO2 has been as high as 7000 ppm.:

Figure 1a. Source: Pagani (2005 and Anthony Watts.

Another chart of the last same period showing the 7000 ppm maximum is Figure 1b below. The difference between Figures 1a and 1b appears to be that 1a shows temperature anomaly (relative change) while 1b shows the absolute temperature.

Figure 1b. Source: Ice Age Now.

In the next graph, we see that the levels of CO2 have been dangerously low for roughly the last 3 million years.Here is a more detailed graph of the last 800,000 years:

Figure 2. Source: Lindsey (2020)

There have been 5 inter-glacial periods over the last 400,000 years. Current CO2 levels are in line with the earlier 4 periods. The concern should really be how brief on a geological time scale these maxima are.

Euan Mearns presents a number of graphs of the Vostock ice core data covering the last 450,000 years. It is the most instructive of the long-term datasets:

Figure 3. Source: Euan Mearns (2014)

Note that you are reading the graph left to right from present to 450,000 years ago. As Mearns notes:

CO2 and temperature appear well-correlated in a gross sense but there are some significant deviations. At the terminations, the alignment is as good as observed for methane. But upon descent into the following glaciation there is a time lag between CO2 and temperature of several thousand years. Petit et al [1999] make the observation but fail to offer an explanation and to take the significance into account preferring to make instead unsupportable claims about CO2 and CH4 amplifying orbital forcing.

In other words temperature leads CO2. If causation is involved in the relationship, then temperature causes CO2 levels and not the reverse.

More Recent CO2 Records

The Law Dome ice cores were extracted in Antarctica from 1987 to 1993. Data from the cores extend from 1010 to 1975 AD and appears next shown the data smoothed using a spline fit with a 75 year cutoff:

Figure 4. Source: CDIAC[1]

The beginning of the modern rapid increase in CO2 is about 1850, more than a century before the period when ‘global warming’ appears to begin.

Modern Era Data

The longest continuous measurement that we have of atmospheric CO2 began in 1958 by the Scripps Institution of Oceanography at Mauna Loa in Hawaii. NOAA began measurements in 1974 at its Global Monitoring Laboratory. The combined data is shown below. Point Barrow data looks similar[8].

Figure 5. Source: NOAA[2]

What Level Is Best?

In the modern greenhouse, plants grow optimally in the 1,000–1,300 ppm range[6] with 1500 ppm appearing as an optimal number frequently in the literature.

There is, however, a minimal level after which photosynthesis stops and all plant and therefore animal species die. An experiment by Gerhart and Ward (2010) showed the poor growth response of Abutilon theophrasti at 150 ppm:

Figure 6. Source: Gerhart and Ward

NASA has noticed that increased atmospheric CO2 levels have increased leaf cover in global forests by as much as 50% or more[11]:

Figure 7. Source: NASA

CO2 As a Greenhouse Gas

The key aspect of this topic would require some significant knowledge of chemistry and physics. As such, we’ll leave the discussion to the experts in the next section. However, the next chart breaks down the percentage contribution of the components to the greenhouse effect. The concentration of CO2 alone in the atmosphere is 0.04%.

We would note that water vapour is not accurately represented in current climate models as ongoing research s beginning to reveal (SuspiciousObservers regularly reviews climate research and has an extensive bibliography for members)..

Figure 8. Source: unknown

What the Experts Say

Here is Dr. Patrick Moore on CO2 (20:32 minutes):

Here is a presentation by Dr. Willie Soon (1:15:21 minutes):

Let’s include Dr. William Happer (36:58 minutes):


  1. Historical CO2 Records from the Law Dome DE08, DE08-2, and DSS Ice Cores. CDIAC. Links to graphical representations and data.
  2. Trends in Atmospheric Carbon Dioxide. NOAA.
  3. Pagani, M., Zachos, J.C., Freeman, K.H., et al. (2005). Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene. Science  22 Jul 2005: Vol. 309, Issue 5734, pp. 600-603. DOI: 10.1126/science.1110063. Behind a paywall.
  4. Anthony Watts. Dr. Vincent Gray on historical carbon dioxide levels. Watts Up With That? June 4, 2013.
  5. Lindsey, R. (2020). Climate Change: Atmospheric Carbon Dioxide. NOAA, August 14, 2020.
  6. Carbon Dioxide In Greenhouses. Ontario Ministry of Agriculture, Food and Rural Affairs, December, 2002.
  7. Laci M. Gerhart and Joy K. Ward. Plant responses to low [CO2] of the past. Tansley review, 5 July 2010.
  8. R.F. Keeling, S.C. Piper, A.F. Bollenbacher and J.S. Walker. Atmospheric Carbon Dioxide Record from Point Barrow, Alaska. CDIAC.
  9. Euan Mearns. The Vostok Ice Core: Temperature, CO2 and CH4. Energy Matters, December 12, 2014.
  10. J. R. Petit, J. Jouzel†, D. Raynaud, et al. (1999) Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature,Vol 399, 3 June 1999.
  11. CO2 fertilization greening the Earth. Boston University, April 25, 2016.