6. The Age of Man

by Eric Grimsrud

In this post, I will summarize the countless effects man has had on physical aspects of the Earth.   With each of these components, I will used select figures which I believe are worth a “thousand words”, as they say, and allow me to use a minimum of my own.
In addition, I will not include here all of the details, numbers and data that could be included in support of each component.  I will be pleased to do that, however, wherever I am asked to justify or clarify any of the components.  Since many of these components are generally accepted, I don’t anticipate having to justify all of what I will present here and have not assumed at the start that I know which parts will require further justification.  Also at the very end of this post, I will state what my hypothesis is concerning the issue and details associated with AGW and, of course, will then entertain questions and comments before turning to the “Jury” for their response.   So let’s get started.

What follows with be a presentation of information delivered under the follow components:

  1. The Period of Man’s Major Influences  (length will be short)
  2. Has CO2 Increased and how much? (short)
  3. Has Temperature increased and how much?  (long)
  4. What Else Contributes to Climate Change?  (moderate)
  5. What will 2100 Look Like with Business as Usual (B as U)? (moderate)
  6. Hypothesis (short)

The Period of Man’s Major Influences:


Figure 1, While Man has been on Earth for much longer than 10,000 years, his total population began in increase and then soar only after developing advanced civilizations during the last interglacial period known as the Holocene. During the last portion of the Holocene, the total population increased exponentially and especially after the Industrial Revolution began in about 1850.  By 2050, it is expected that the  population of Earth will be about 9 billion.

The amount of CO2 produced by Man over the latter portion of the Holocene is shown in Figure 2 below, which requires no additional explanation here.

Has CO2 Increased and how much?

First consider the ice core date shown in Figure 3.

Figure 3.  The inserted figure shows the CO2 content over the last 1,000 years.  The last entrée shown in black are from the Keeling Curve of modern measurement of our atmosphere while all other date is from the analysis of CO2 trapping in the ice cores.  Note that CO2 levels have been close to constant over the Holocene at about 280 ppm until rising sharply at the beginning of the Industrial Age.

A closer look at modern measurements of CO2 in the background atmosphere is shown in Figure 4 below.

Figure 4.  Generally known as the Keeling Curses these data show the CO2 levels of the Northern Hemisphere and the Southern Hemisphere, in these cases monitored at excellent sites for background CO2 measurement for CO2 (that is, site far removed from sources and sinks of CO2).  Note that the “breathing” of the Earth is greater in the NH than the SH due to its greater fraction of vegetated land surface. Note also the slightly high levels of CO2 in the NH suggesting  higher anthropogenic emissions of CO2 in the NH.

The rate of CO2 increase is presently about 2 ppm per year and is thought to be increasing slightly.  At this rate (the Business as Usual scenario) we can expect the CO2 level to have doubled during the Industrial Age from 280 to 560 ppm well within this century and probably by about 2080.

It is also very important to note that the emissions of CO2 by Man, shown in Figure 4, which are actually very small compared to those of Mother Nature have resulted in the great increase of 40%.  This is due to the very slow rate at which the EXTRA CO2 is removed from the atmosphere, a subject to be dealt with more directly later.

It should also be noted that concentrations of other GHG gases, including methane, nitrous oxide and tropospheric ozone, have also increased during the age of Man (while stratospheric ozone has actually diminished).  Since the contributions of these to climate change are thought to be of secondary importance, so far, and since the emphasis of this debate is centered on questions concerning fossil fuel use, we will not get into as many details of these GHG’s here.

So Has the Earth’s Temperature Increased and, if so, How Much?

There have been many indicators of T change and some of these are more convincing than others.  For starters, let’s begin with Figure 5 below, which speaks for itself and, I’ll admit, is one of those indicators of interesting, less convincing nature!

Perhaps good old temperature measurements using good old (and new versions of) thermometers would provide a better starting point and these are shown in Figure 6 below.


Figure 6.  Note that due to natural year to year variations, only decadal changes are considered to be provide a meaningful indicator of global average temperature change. On that basis, it does appear that the Earth’s temperature has increased over the last 3 decades by about 0.5 degrees C.

There are other proxy measurement of temperature changes over the last several centuries such as those found in Figure 7.

Figure 7.  Temperatures over the last 10 centuries deduced from proxy measurements such as  tree rings and ice core samples. Because the precision and accuracy of these measurements is lower than direct temperature measurements the validity of the “hockey stick” thereby produced has been a point of debate and controversy.  However, its suggestion that the temperature has increased significantly over the last 50 years has not been significantly disputed.

There are, of course, many additional indicators of temperature increase in recent years.  The loss of sea ice in the Arctic is obvious and is at last providing us with a long sought “Northwest Passage”.  Another, of course, is the loss of glaciers throughout the world as illustrated in Figure 8 below:

Figure 8.  Photos of an Alaskan glacier.  For those looking for upsides of these changes – note the increased vegetation in the more recent photo.  As for downsides – more below.

Just as with the glaciers, modern satellite based measurement of the gravity pull of the Earth’s surface has detected measureable losses of sheet ice from both Greenland and Antarctica. These loses, of course, are expected to contribute directly to increases in sea levels.

Speaking of sea levels, Figure 9 shown the measured change in these over the last 130 years.

Figure 9.   The most recent measurements, shown in red, are from modern satellite- based method.   Some (about 3 cm) of the 20-cm increase observed over this period can be explained by the thermal expansion of the oceans over this period.  Some (perhaps another couple centimeters) can be explained by the melting of sheet ice.  The reason for about half of the sea rise noted to date remains a mystery, however. As pointed out by William McClenney in his comment #78 under our “sea level” category, much of this additional rise in sea level might be coming from the extraction of ground water and its subsequent passage to the oceans. In any case, due to increasing losses of ice from Greenland and Antarctica, future significant increases in sea level can be expected.

For some perspective on the 20-cm rise shown in Figure 9, consider Figure 10

Figure 10.  Shows the change in sea level measured over the latter portions of the Holocene during which advanced civilizations, based on agriculture and sea life where developed.  Note that sea levels have been relatively stable (to within about a meter or so during the last 2,000 years.

Another indicator of climate change is provided by the increased frequency of storms (for which I will not provide evidence of here unless requested to do so).  This is expected if the amount of water vapor is increased in the atmosphere.  It is the energy involved in the evaporation and condensation that causes temperature and pressure gradients within the atmosphere, thereby provided the power behind extreme weather events.

Many indicators of temperature increase are being provided by the world’s “critters”.  For example, when I moved to Bozeman MT in 1975, I replanted a large number of lodgepole pine on my new yard.  When I moved away from Bozeman in 2004, they were big, mature and healthy.  Today they are all gone due to the explosion of  pine beetles which, back in the good old days, were knocked back every winter by exceeding cold spells that seemed to visit us every year – and my Lord, do I have some stories about them!!!).  Biologists are continuously coming up with other temperature related explanations for myriad changes in the migration and population changes of other critters.

Another suggestion that temperature change is and will continue to occurs as the level of  CO2 rises comes from our observations described in my previous Post 6 of our previous atmosphere as revealed by ice core and sea bottom measurements. In addition, those measurements suggest that temperature will increase by about 3 degrees C in about 2080 relative to 1850 and about 2 degrees C relative to today.  In addition as CO2 levels then persist in centuries to follow, the Sensitivity of CO2 can be expected to increase gradually from about 3 to  6 degrees C, as long-term feedbacks start to kick in (for example, as the altitude of the top ice in Greenland and the Antarctic begin to drop the temperature that the top ice is exposed to increases and more melting occurs). Without repeating what has already has been said in Post 6, I will just remind us here that the correlations between CO2 and temperature changes described in Post 6 were provided to us by observation of what Mother Nature has done in the past.  Note also that in the more ancient world from about 50 My years ago, the T change appears to have followed changes in CO2 which during the more recent glacial-interglacial period, CO2 change appeared to follow T changes.  So, it does not appear to matter which comes first.  Through the feedback systems, T and CO2 change roughly in concert with each other, given the time required to do so.

Lastly, we have an enormous additional source of information that we can refer to as needed.  This is that provided by computer-based simulations of the Earth’s atmosphere.  I am not going to go into that here myself for two reasons.  One is that I cannot adequately defend the accuracy of the predictions of that field myself because I have no real experience in it (other than noting their results).  Another is that I have noted that even these modelers of climate change use the history data of the type we have discussed here as their “reference” points for testing the validity of their models.  In other words, they agree that the information provided by history is the most reliable.

Nevertheless, I believe that their predictions concerning the future are very much worthy of consideration and some of them are shown below in Figure 11.

Figure 11.  These are the predictions of future T changes if Business as Usual continues throughout the present century.  These result from the variety of different models indicated by various colors.

It should also be noted that any prediction of T increase more than 2 degrees C relative to the present is thought to be distinctly “bad news”, as is summarized in Figure 12 shown below.

In assessing Figure 12 above, it might at first seem surprising that such small changes in global average temperatures could cause the great changes suggested here.  In order to better appreciate this, it is useful to remember that the average global T changes that occur between glacial and interglacial periods is only about 5 degrees C !!.

Also, it is important to note that the changes predicted here is towards relatively NEW TERRITORY, never experienced during the glacial and interglacial period of the last 2 million years.  We are headed back towards the much warmer and more ancient areas also discussed previously in Post 6, where both temperatures and sea levels were very high (70 meters higher about 35 My ago when there was no ice anywhere and about 200 meters higher 50 Mys ago, due to additional thermal expansion).

What Else Contributes to Climate Change?

In Figure 13 below, the major forces for climate change that have been thought to be operative since 1880 are shown.

Figure 13.  First, the red curve shows the total forcing of all of the GHG’s from 1880 to the present.  This appears is the dominant, but certainly not the only strong force operative over this period.

The blue line shows the equally large, but episodic forces in the opposite direction that have been caused by unusually large volcanic eruptions that punched particulate matter into the stratosphere (the particulate matter from smaller volcanoes that penetrated only into the troposphere is washed out of the atmosphere very rapidly). Once in the stratosphere the increased albedo cooling effect of this particulate matter lasts for a few years (about three).  It is interesting to note that the CO2 that is simultaneously emitted by these large volcanoes, such a Pintatubo in 1991 do not contribute significantly to background CO2 levels as have been shown by the Keeling Curves in Figure 4.

The solid pink curve in Figure 13 indicates the increased albedo cooling effect of particulate matter in the troposphere which has been put there my man’s emissions of oxides of nitrogen and sulfur.  These molecules quickly become particulates after their further oxidation in air.  While these substances will be quickly removed from the atmosphere by natural processes, their steady state levels are maintained by the continuous emissions of SOx and NOx, as these oxides are called.  As can be seen in Figure 14 the cooling effect of these particulates is thought to be about 35% as great as the warming effect of the GHG’s today.  As Man is getting better at eliminating the emissions of NOx and SOx from common sources such as automobiles and coal-fired power plants, it is expected that cooling due to these anthropogenic sources will decrease in the future while the Forcing from the GHG’s continues to climb (assuming B as U continues).

The dashed pink line in Figure 13 provides an estimate of the corresponding cooling effect of the tropospheric particulates via their tendency to increase cloud formation.  Like clouds themselves, this contribution to total forcing is not well understood (recall that clouds cause both cooling and warming).

The effect of another type of man-caused particulate matter is shown by the solid back line.  This form of particulates is called “carbon black” and is uncombusted soot that typically comes from coal-fired power plants and diesel engines.  Note that the Forcing caused by this form of particulates is towards warming – due to their absorption of incoming solar radiation, thereby decreasing the Earth’s albedo.  This effect is also expected to diminish in the future with improvements in antipollution technologies.

The wavy red line of small amplitude provides the small effect on Forcing provided by oscillations of the Sun’s intensity measured over this period. The effects of changes in land use and snow coverage are also included and are also relatively minor contributions to total change over this period. One of these contributes slight to warming (diminished snow coverage) and the other is thought to contribute slightly to cooling.

The net sum of all of the forces shown in Figure 13 are shown in Figure 4 of my Post 6 – by the black line shown in the right portion of that graph.  It is shown there that in the last few decades, Forcing by the GHG’s has become dominant over all of the others.  Note also, that with anticipated improvements in antipollution technologies for reducing atmospheric particulates, in the future we can expect that the net Forcing of the black line will move progressively higher towards that of the green line in Figure 4 of Post 6.

So, What Will 2100 Look Like with Business as Usual (B as U)?

If B as U continues, we can expect that the level of atmospheric CO2 will be at least 600 ppm (with the doubling point of 560 ppm having been passed at about 2080).  Because I believe that the fast feedback Sensitivity of CO2 is about 3 degrees C, I believe that the temperature in 2100 will be about 3 degrees C greater than the preindustrial level and about 2 degrees higher than today.  This estimate includes a cooling effect of about one degree from the other Forcings described in Figure 13,  along with the assumptions that we will continue to reduce particulate pollution and will not have intentionally indulged in geoengineering schemes, such as the intentional addition to SOx to the stratosphere.  In view of Figure 12, I believe that this level of temperature increase would be extremely detrimental to existing conditions on our planet.

Worse still, would be the continuation of the then GHG’s Forcing established by 2100 even if we then started to decrease CO2 emission.  Again, pictures are worth a thousand words concening this statement, so first see Figure 14.

Figure 14 shows where we believe an imaginary single “plus” of extra CO2 would go if suddenly released into the atmosphere.  It is seen that a significant fraction of it remains in the atmosphere essentially “forever” on a time scale of relevance to human civilizations.

Now consider Figure 15.

Figure 15 shows expected future atmospheric CO2  levels predicted under realistic scenarios for CO2 emissions and cutbacks (these calculations are based on the fates of CO2 indicated in Figure 14).  The B as U scenario we have envisioned here is even less ambition that that shown by the top maroon-colored lines. (Note that my rough estimate of a least 600 ppm by 2100 is similar to that of slightly more than 700 ppm predicted here).

I believe that the magnitude of GHG Forcing achieve by 2100 with B as U would put us on a long term track in the direction of  an ice free world with distinctly unpleasant events (as described in Figure 12) occurring along the way – as well as sea level rises of several meters within the next few centuries. For support of this statement, go back to my Post 6 and have another  look at its Figure 1.  Note that about 35 Mys ago, we experienced a transition from an ice free world to the Last Major Ice age because the CO2 level had dropped to roughly 450 ppm at that time.  Note that we are presently at 392 ppm and will be above 600 ppm by 2100 with B as U.  The resulting GHG Forcings would then  be expect to “chew away” aggressively at our vast sheets ice on Greenland and Antartica – where about 75% of the fresh water of the Earth presently resides.  Even if  that chewing process lasted only a few millennia, it would make a good dent in that total mass of ice and cause extensive changes to existing conditions in the meantime.  What is more likely, however, is that warming trend would continue once begun as the slow feedback Sensitivity of about 6 degrees gradually kicked in after a few centuries – as the altitude of the top of these ice masses continuously decreased to warming levels. There would also be the possibility of methane releases from warming permafrost and methane clathrate deposits to consider.



Ample physical evidence shows that CO2 is the single-most important climate-relevant greenhouse gas in the Earth’s atmosphere.  Along with the other non-condensing GHG’s, changes in CO2 levels facilitate temperature changes which are then amplified by the large feedbacks provided by accompanying changes in water vapor and clouds.  In addition, albedo changes are also coupled to these temperatures changes in a manner that further encourages temperature changes in the prevailing direction.  The magnitude of the Climate Sensitivity to CO2 is about 3 degree C for shorter periods of a few centuries or less and about 6 degrees C for longer periods of a few millennia or more.  These values of Sensitivities have been suggested by observations of the past 50 My years and are likely to continue to apply in the foreseeable future.  Recognition of these magnitudes along with observed CO2 increases over the last 160 years strongly suggest that our  planet is already significantly out of balance with respect to historic Forcings that have been in place during the Holocene – during which human civilizations developed.  In order to avoid the great risks to existing civilization that these pending changes might very possibly cause, we should do everything we can to stop CO2 emissions as soon as physically possible and, more than that, try to figure out how we can get our existing level of 392 ppm back down to about 350 ppm.

It just happens that a recently published article (“Atmospheric CO2: Principle Control Knob Governing Earth’s Temperature” by Lacis, Schmidt, Rind and Ruedy, SCIENCE, vol. 330, October 15, 2010, pages 356 – 359) expresses my basic hypothesis perfectly.  If you can get a copy, please read it for greater detail concerning this hypothesis.