Carbon dioxide concentrations and temperature changes over the last 540 million years.

Over the last 540 Million years, over what is termed the phanerozoic, life evolved that is large enough to see in the fossil record with the unaided eye. During this time there have been fluctuations in temperature and carbon dioxide and also five mass extinctions most of which at least are related mainly to these changes.

An understanding of these changes is consistent with our understanding of today’s changes we see due to the greenhouse effect and in particular the role played by CO2. There are other factors that are involved in the changes of climate over this period and so the correlation of climate and CO2 is not at first obvious. When other factors are considered it becomes clear that CHANGES to climate are very closely related to changes in CO2 not only today but throughout the time of complex life on Earth.

Unfortunately there are some who want to discredit climate science that ironically ignore these other factors to try and persuade through a simplistic approach there is no correlation or indeed understanding of these changes.

As we look back in time the possible ranges of estimated values for CO2 and temperature become generally larger, however it is not possible to understand these changes in temperature without including the greenhouse effect of CO2. Only by realising that CO2 plays a major factor in controlling the Earth’s temperature then a self consistent explanation can be given that stands up to quantitative scrutiny.

A few clearly flawed arguments have been made to dispute this:-

  “Where does carbon dioxide fit into the picture?...not as neatly as you might think. CO2 and temperature levels do not show a strong correlation.......we find the climate changing for reasons we don’t fully understand.”  Patrick Moore

Patrick Moore makes these statements in an online video over a background of oversimplified graphs of co2 and temperature changing over the complete Phanerozoic period of around 540 millions of years. He then concedes that there are many other factors but fails to make any attempt of showing how these might fit in with carbon dioxide to explain changes over this time period. Instead he then proceeds only in describing Milankovitch cycles that occur over much shorter time scales due to the changes in the earth’s tilt and orbit around the sun. Changes that we do not have a fine enough resolution to know about 100’s of millions of years ago and regardless could not possible show up in the scale of the graph he had chosen to infer that there was no correlation between CO2 and temperature.  (The Milankovitch cycles that can only be seen in the more recent records due to their relatively short time scale can also be explained by the contribution that CO2 plays, but that is a separate myth that Patrick Moore infers along with a gish gallop of myths that he raises).

So let us look at where Moore might have helped in describing how CO2 does fit into the picture over the last 500 million years and what he had failed to do.

1.  Stellar evolution:- From stellar physics it is known that the sun has gradually increased in strength and over this period of time this is around 4% stronger now that it was at the start of the phanerozoic. If this factor is ignored then it is not possible to see the correlation of CO2 and temperature. This is the main factor and most easily quantifiable that is ignored when one wants to misrepresent this situation and claim no correlation.

2. Resolution issues:- Although we have a fair idea of levels from fossil records and other proxies, there are fairly large uncertainties in both CO2 and temperature estimates particularly as we look further back in time. In particular the temperature variations that Moore selects are a very unjustifiably oversimplified representation for the purposes of making comparisons.
If there was any short term dip in the CO2 levels that were only of a million years or less these would not show up in the record when we look back over half a billion years but could initiate an ice age with higher levels of CO2 than today. (due to the weaker solar radiation)
There are periods when the Earth was frozen and periods when the earth was not frozen that are clearly identified in the records.

3. The Albedo effect:-  If the Earth is frozen then much more sunlight is reflected. Therefore the same levels of CO2 and/or solar strength will not necessarily result in the same temperature produced when comparing different time periods in the record separated by millions of years.

4.Reduced silicate weathering:-  The levels of CO2 naturally build up slowly during ice ages due to the reduced silicate weathering from rocks (which otherwise removes CO2 from the atmosphere).  Since the land is covered in ice the rocks are not exposed to the atmosphere.  Higher levels of CO2 over longer periods of time that would show up in the record are required to get out of the ice age due to the increased albedo effect.

(This combination of the albedo effect and reduced silicate weathering results in a hysteresis loop effect.  This further complicates the temperature and CO2 records.)

5. Quantification:- Climate scientists do know how to quantify these effects (and other changes such as continental movement that has occurred over this time changing ocean circulation and the likelihood of ice build up over the poles) and hence have a greater understanding than those like Moore who have failed to attempt to explain these.

 It is difficult to know what Moore means when he says “we find the climate changing for reasons we don’t fully understand”.  Is this an admission that he and the contrarians who have used this debunked argument in the past don’t understand the factors that cause climate to change, or is he inferring that these quantitative methods are not known to scientists, or yet again is he using the impossible expectations fallacy that there are some details that are not understood and hence wrongly implying nothing is understood?

However it is ironic that those who support Moore’s viewpoints of selecting unjustifiably precise versions of these graphs over 540 million years into the past without uncertainties but question the temperatures that we have much better accuracy today. It is further ironic that Moore who denies the role of CO2 also denies the solar changes that have occurred over these large time scales.
As an example of the quantitative understanding consider variations in solar activity. Our sun is increasing in intensity by just less than 1% every 100 million years.

The faint young Sun problem Georg Feulner

Important note on the magnitude of the trend in solar evolution.

To put this in perspective the trend over 10 million years is of the same magnitude of the cyclic variations that we see in the 11 year solar cycles. This means that this trend is about a million times smaller (over a decade) than the magnitude of the changes in the 11 year solar cycle (over a decade) and hence this trend can be ignored for example when looking at changes in climate today or of changes when we see the swings in temperature in and out of ice ages that have occurred in the paleo-record. These swings have much more to do with the changes in CO2 whether as a forcing or a feedback to some other change However when comparing climate over 100’s of millions of years we cannot exclude this trend as Moore and a few others have.

A 4% change in solar activity can be easily shown to have a forcing impact of around 9.5W/m2 ignoring feedbacks that would require around a six times increase in CO2 to compensate.

Using the knowledge of the factors that affect climate it can be shown that CO2 indeed correlates well with temperatures over the last 500 million years.

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