Limitations on Anthropogenic Global Warming
Posted by Jeff Condon on May 19, 2009
I was going to work on replicating the EIV reconstruction for Mann08 but ended up watching a hockey game at someone elses place so Mann gets another days repreive. Tonight I have a guest post by Dr. Leonard Weinstein senior research scientist from Nasa.
Dr. Weinstein left a link on one of my threads and I asked if he minded if I call attention to his work. He replied with a request for a few posts he’s done which look critically at the heart of AGW science.
Limitations on Anthropogenic Global Warming
Leonard Weinstein, ScD
March 1, 2009
It is not obvious what the ideal temperature and CO2 level should be for mankind. We tend to assume that the average of whatever has occurred in the recent past is the ideal level, since we have adjusted to that level, and changes from that level can cause disruptions in living conditions and activities. Significant temperature and CO2 increases in recent years have raised the issue of whether these were possibly related and were due to human activity, and whether this is a potentially significant problem.
Earth’s temperature has only been directly measured at enough locations to give a reasonably accurate global average for about the last 150 years, with the greatest accuracy (from satellites) only going back about 30 years. The “reliable” CO2 background level has only been directly continuously measured at one location (Mauna Loa) for about 50 years, and at a much larger number of locations for about 30 years. Some other direct and indirect CO2 measurements were made prior to 50 years ago, and the measurements thought to be most reliable were used to extend the CO2 curve back to 1850.
Figure 1 is a commonly used figure to show smoothed global variations of the temperature and CO2 concentration data from 1850 through 2000 AD. This data indicates the Earth’s surface has warmed about 0.7OC (1.3 OF) and the atmospheric CO2 appears to have increased by over 30%. These two pieces of information are the basis for the present “Anthropogenic Global Warming issue”.
Figure 1. Variation of global average temperature and CO2 concentration over last 150 years
(Sources for temperature and CO2:
A more recent version of the temperature anomaly for the period 1850 through 2008 is shown in figure 2. The data, from
is also shown as a smoothed yearly variation, including range of uncertainty.
Figure 2. Yearly anomaly of global temperature variation from 1850 through 2008
This newer data somewhat modifies the conclusion that had been inferred from the more limited temperature curve from figure 1, where the belief (supported by the IPCC) was that the increasing CO2 was the main cause of the increasing temperature. The temperature trend has peaked about 2002 and then rolls over and starts trending downward rather than continuing to rise as predicted. This apparent reversal contradicts the predicted trends in the IPCC models. While the downward trend has occurred only a over a few years, the entire period used to justify the “Anthropogenic Global Warming issue” is not much longer (1970-2000), and the 1970 level is significantly below the 1941 level!
There are several indirect ways to determine temperature variations that extend the record back much further than 150 years. These include (but are not limited to) historical written records, information from tree rings, glacier ice cores, sediment deposits, and borehole temperatures. The accuracy and distribution of these methods for the global average is thought to be fairly good to about 400 years ago. However, the limited number of locations for these records as we go farther back in time tends to decrease the absolute levels of confidence of the indirect records for an average global temperature prior to 400 years ago. The trend can be extended back about another thousand years or so, but with decreasing confidence in the global average the farther back you go. A few local sources showing temporal variations can extend the record back much farther in time, but these are not global averages.
Tree ring data can extend the temperature trend record back several thousand years, but do not give reliable absolute levels due to sensitivity to parameters such as being restricted to land, and having unknown rainfall, Solar insolation, local CO2 level, etc. They also do not show winter or nighttime data, and are thus not truly average temperature indicators. Borehole data is limited in temporal resolution, and only goes back reliably a few hundred years at most. In the end, glacier ice core data at a limited few locations, and sea floor sediment cores, are the most reliable and longest period data sources for temperature. The CO2 variations are also claimed to be obtainable from glacier ice cores, going back hundreds of thousands of years, but a question of the validity of that claim is discussed in more detail later in this paper. A combination of data from several techniques indicate that the average surface temperature was relatively warm about 1,000 years ago, and this period was called the “Medieval Climate Optimum”. This changed about 1,200 AD or so into a prolonged colder period called the “Little Ice Age”, which lasted until about 1850. The temperature variations were not uniformly distributed and it is not clear if the “Little Ice Age” extended to the southern hemisphere. The accurate average level of the temperature that occurred during the “Medieval Climate Optimum” and the speed at which it changed were not able to be reliably determined, due to the limited number of data points, and increased uncertainty in accuracy of many of the sources that far back in time.
The AGW proponents claim that the magnitude and level of the present global temperature, and the speed in which it increased, is unusually extreme and cannot be accounted for by natural variations. They claim the observed temperature increase is being caused by human activities such as the burning of fossil fuels, deforestation, and manufacture of cement. The observed recent increase in CO2 (and also Methane) is thought to have increased the greenhouse effect of atmospheric gases to trap more radiated heat and thus raise the surface temperature. In order to examine the AGW claims, temperature data is shown in figure 3 from three widely separated sources. The data covers the last three thousand years for a representative Greenland ice core and Sargasso Sea sediment core, and the last two thousand years for an Antarctic ice core (all data taken from web sources, including NOAA).
The ice core data was taken from locations on glaciers that had minimal lateral substrate movement, and did not melt on the surface in the summer. The yearly snow variation was sufficient to accurately identify the year of the layers in the compacted solid ice core. Oxygen isotope ratios were used to determine the temperature, and the data shows the variation in temperature relative to the year 2000. The Sargasso Sea sediment core temperature data were obtained from the Oxygen isotope ratio of the surface-dwelling planktonic foraminifera, and shows the sea surface temperature for the last 3,000 years. Conclusions from these curves are:
The temperature varied several times over the period by 1.5 OC to 2OC for all three curves
Temperature variations occurred fairly rapidly, with typical time scales of 50 to 200 years
The rise rate over the last 150 years is not unusual compared to other rise rates
The present level of temperature is near the average for the curves shown for both Northern hemisphere cases, and below several previous peaks
The “Little Ice Age” and “Medieval Climate Optimum” show up in both Northern hemisphere cases
The present temperature is not unusually high for the Antarctic
Figure 3. Temperature variations from the Greenland glacier ice core, the Sargasso Sea sediment core, and the Antarctic ice core. All 3 curves have lined up dates, and have the same vertical scale size.
The trend of the temperature for the Greenland and Sargasso Sea curves is also generally decreasing from 3,000 years ago, and the “Little Ice Age” was a cold and long lasting period. There are several other locations with indicated local temperature variation in this time period that generally tend to agree with the extent of the temperature variation during the little ice age and medieval climate optimum, and all show large variations occurring over the entire time period. If the present temperature is not unusual based on the above comparisons, why the AGW claims? In fact, it is based on two observations:
The temperature has been warming over the last century and has increased the most within that period in the last 30 or so years.
The CO2 and Methane levels have increased a lot over the last 30 to 60 years, and ice core records show them to be higher than any other time in the last several hundred thousand years.
It is clear that we get excited at anything different that happens in a time period that spans a large fraction of a lifetime, and even dominates recent history, even if it is not unusual compared to time periods more distant in the past. Also, the claim that increasing CO2 (and Methane), likely with a significant contribution from human activity, can cause some global warming does have some theoretical and computational basis. The problem is that all of the physics governing the Earth’s climate, including ocean currents and cloud feed back, as well as particulate effects are not fully understood, and generally are put into models in artificially selected forms to try to force the models to agree with actual measurements. A discussion of one possible problem with the theories and models is made in:
If we go back even further in time for the present interglacial period than shown in figure 3, even higher temperatures and larger temperature variations are encountered. While we clearly are presently in a period of warming (or at least were up to the last few years), there is no indication that this is an unusual period of warming! If the present were unusual, then all previous times of rapid change and high levels would also have to be unusual, and where is the anthropogenic causes for those times? However, it is not certain that anthropogenic causes are not significant factors in the recent warming, so a “what if” case has to be examined. For the following, the assumption is made that the CO2 increase is dominated by human activity and that this increase is assumed to be the cause of a significant part of the temperature rise. Five questions need to be addressed:
1) Is it likely that the anthropogenic greenhouse gas levels will continue to increase?
2) Has the increase in anthropogenic greenhouse gasses been the dominant contributor to the recent high global average temperature?
Are there other problems (or advantages) from increasing CO2?
Is it likely that the temperature will continue to increase significantly (and if it does, is this necessarily bad)?
Has this temperature rise (whatever the cause) had a significant effect on rising sea level and changes in weather?
The answer to the first question is probably yes. However the rate of increase is less certain, since the present increasing trend may only be a transient lag in the ability of the Earth to come to a new equilibrium from human activity. The level will probably remain higher than previous levels, but when it will eventually level off, slow down, or just keep increasing, is not clear. A CO2 level of between 400 and 500 ppm, or even a bit higher may be possible (but not certain) by 2100 absent heroic efforts to reduce the rise. There is no reasonable basis for increases much beyond this, mainly due to the finite availability of easily obtained carbon based fuels. It should also be noted that the methane level, which had increased considerably from prior to 1850 to the mid 1990’s, has essentially leveled off for the last decade, so is not a factor in additional warming.
Question 2 can be restated as: how much of the temperature increase in the last 150 years is due to the CO2 (and methane) increase, and how much due to a general recovery from the Little Ice Age. I don’t think we can accurately answer that, but it appears almost certain that human activity did not cause much more than about 0.3OC of the increase, based on the net rise from the local peak from about 1940 to the latest trend at the end of 2008. This maximum plausible contribution is much less than the expected increase blamed on human activity for this time period. The larger portion of temperature rise occurred prior to most of the input of CO2, so that rise cannot reasonably be blamed on this cause. In fact, the temperature had already increased somewhat from 1600 to 1850, so the rise from 1940 to 2008 is only about 1/4th the actual total rise (~1.2OC) from the low around 1600. From this we can conclude that anthropogenic increase in the CO2 may have contributed to the recent warming, but at most only a very modest share, and the present temperature trend is down!
This modest increase also brings up the issue of the calculation of expected temperature increase from models. These models directly calculate the expected increase from greenhouse effects, and then add expected positive feedback effects due to increased water vapor caused by the higher temperatures. The models (including positive feedback) anticipated a total rise of ~1.5OC just due to anthropogenic causes from 1850 to the present. It appears they are at least a factor of 5 too high if only 0.3OC of the increase was due to the greenhouse gasses as stated above. In fact, the main part of the temperature increase was clearly a recovery from the little ice age, and occurred prior to the vast majority of CO2 increase! There are also models that anticipate a negative feedback from increased water vapor forming the types of clouds that reduce the heating. It is not yet certain why the temperature is at the present level, but it is clear that the models have not yet been demonstrated as valid!
The temperature drop between 1940 and 1970, along with the underperforming model estimates were recently blamed on “Global Dimming” caused by particulate pollution. In fact the particulate pollution took a large dive when oil and gas rather than coal became major home and business fuels many years earlier (as seen in glacier records). More recently, particulates from growing economies like China, along with aircraft contrails, have added more dimming in recent times. The prediction has been made that once we (and the Chinese?) clean up pollution, this dimming will decrease and warming will be even worse than previously predicted. This presumes that greenhouse gas output is a separate problem from particulate pollution, but it is more likely that they will go up or down together.
A more recent study has concluded that an ocean current (Pacific Decadal Oscillation) not previously included in the “Global Warming Models” will dominate the effect of greenhouse gas temperature increases for about a decade or more (until about 2015 to 2030), and that this is the cause of the unexpected reversal of temperature trends for the last several years. It is curious that this new factor was not found until the temperature trend reversal became clear. It appears new factors will be found as needed to explain any deviations from the present “understanding of the Global Warming Problem”. Since the entire time of temperature rise used to show that there is an unusual period of heating was only about 30 years long (1970 to 2000), it now appears that we are told by global warming modelers that 30 years of a selected time of heating, sandwiched between one 30 year period of cooling, and being followed by another period of cooling (of unknown length, but at least 10 or more years), is proof of their claims – because it is a period of a local maximum temperature over a period of several hundred years. This despite the clear records that show such rapid variations and even maximum levels are common over the last several thousand years, and that the present level is not even as high as several other previous levels in that relatively recent time period.
The answer to the third question may be that there is a generally positive effect if the only change to the atmosphere was a significant increase in CO2 concentration. Most plant growth increases at higher levels of CO2. It also appears that some concerns for negative effects on ocean life from increased ocean acidity from CO2 were exaggerated, or even totally wrong (as will be discussed more later) (also see
). A significant change in ocean pH would cause some changes, and there would be some winners and some losers in ocean life, but it appears that for realistic level changes this would not be a major problem. In fact, combining the slightly higher temperature with higher CO2 levels should significantly increase world crop growth if these are the only factors, and this is clearly a generally positive effect.
The fourth question combines the question of whether the natural temperature variation combined with the anthropogenic causes of temperature increase will result in significant continued temperature increase. The warming alarmists models predict a rise of an additional 2OC to 5OC as being likely by 2100, but I do not see that as being justified based on present information. Based on a combination of historical trends over the last several thousand years with the recent trends reasonably attributable to anthropogenic causes of temperature increase, it appears that some small additional increase might be reasonably possible (but not certain) by 2100, but most likely within a range < 0.4OC, which would put it in the range of several warm periods in historical times that were particularly productive times.
There are two issues that have to be considered for the fifth question. The first is the effect of rising oceans. The site:
models the expected increase in ocean level due to thermal expansion for a 0.6 OC to 1OC global temperature rise over several decades. They conclude that a total rise of only about 4 to 8 cm. would be caused by the temperature rise. In addition, several studies have concluded that the rise in sea level from Greenland and Antarctic ice cap melt water would not exceed 0.5 mm/year (5 cm/100 years), and this would probably drop off soon or even go negative due to the high altitude of the remaining glaciers, and increasing snowfall adding more ice than is removed by melting. Water from other melting glaciers has contributed to an additional level increase of about 0.5 to 1 mm/year for about the last 150 years, over the general warming trend effect on the oceans. However, much of the added source from melting glaciers is now decreasing, and some glaciers are nearly gone (many of these glaciers were actually formed during the little ice age). The total of all of these contributions is probably less than 15 cm, or 6 inches in the next 100 years, and even much less additional rise in following times. The most interesting point of the sea level problem is that only about 2 to 3 inches of the possible rise to 2100 is even plausibly related to anthropogenic causes of temperature increase, and this is the maximum that would be able to be stopped even with a 100% drop in human contribution! A huge but possible effort costing TRILLIONS of dollars and negatively impacting growing economies most would likely only prevent less than 1 inch of the rise!
A second issue of the consequence of temperature rise is possible severe changes in weather. There have been many claims of super storms, tornados, heavy rain, and drought associated with the temperature changes. Keep in mind that the temperature difference between the low and high latitudes is the driver for these storms, and the main predicted effect of AGW is to DECREASE this difference!! It is very likely that there will be slightly fewer hurricanes, but they may tend to be slightly stronger due to the higher absolute humidity possible with higher temperature. The issue of more frequent and stronger tornados is difficult to evaluate, but records going back about 100 years do not show a significant trend of increasing overall activity of the stronger tornados. There are periods of large numbers and strong tornados going back in history that pre-dated the period of recent warming. The recent severe US tornado outbreak may even have been a record for recorded times (keeping in mind that fairly complete records only cover a very short period), but any one-year record may be unusually large or small, and only longer time trends are meaningful. The average rainfall will likely increase in some locations due to higher absolute humidity possible at higher temperatures, and the locations of high and low average rainfall (and drought) would shift somewhat.
There would be winners and losers in any change in climate and weather, but the overall effect of higher CO2 and slightly higher temperature would be a more productive Earth. The real fact to face is that there always is change in climate and weather over periods of several decades to centuries. We should not make heroic efforts to change the climate but concentrate on being able to adapt to the changes. This is especially important when we do not know for sure if our effort may actually worsen the situation,
The possible problems with CO2 data
The CO2 curve of figure 1 was actually made from three separate parts. The data from one location (Mauna Loa in Hawaii) was used from 1958 to the present. Additional locations started making measurements about 1980, and agreed reasonably well with the Mauna Loa results. A few selected land based measurements made in the previous several decades were also spliced to the Mauna Loa results. Glacial ice core data trends with a large offset time correction were then spliced to the previous two sources (with offset selected to make it fit!). This was then the source of the CO2 curve from 1850 to the present. The ice core data was then also used to show the CO2 variation over the last several hundred thousand years. It should be noted that the CO2 level was obtained directly from gas bubbles trapped in the ice cores.
There are numerous potential problems with some of the CO2 data in figure 1. The Mauna Loa and other recent direct measurements are probably basically reliable as a “background level”. However, far bigger uncertainties occur for the other two parts that made the CO2 curve in figure 1, and also in the longer time ice core records. A few selected sets of direct measured CO2 data made before the Mauna Loa measurements started were used to extend the curve to earlier times. A recent paper by Ernst Beck, who reviewed all of the older direct CO2 measurements, concluded that the papers selected to show the CO2 measurements before Mauna Loa were cherry-picked to agree with prior conceptions. All of the earlier measurements were limited in that they were made over land, and could have been biased by industrial activity, the proximity of cities, agriculture, etc. (and these limitations in reliability could also be applied to tree ring data). In fact Beck’s summary paper shows what may be unrealistic high CO2 data levels, especially in the early 1800’s and the period of the 1930’s, but the point is that this was direct measured data at numerous locations, and generally showed that CO2 levels may have been significantly higher in the near past than claimed. There are no clearly reliable direct measurements in this period that prove otherwise. The best approach probably would be to reject all of the direct measured CO2 data collected before the Mauna Loa and other recent stations were established due to the uncertainty of the applicability of these measurements to determine the global average background level.
The questionability of ice core CO2 determination
CO2 determined from glacier ice core gas bubbles has been used to indicate the atmospheric CO2 level at the time the bubbles formed. The frozen core sample is crushed to obtain the trapped gas from the bubbles and directly find the CO2 concentration. There is no direct supporting evidence that this is a valid technique. In order to examine the reasonableness of the process, the following discussion examines three possible issues.
The first issue arises from the porous nature of the compressing ice, which may take from about a hundred years to possibly as long as thousands of years before it seals off completely. This would result in diffusion averaging of composition, and very likely lose resolving even large variations in atmospheric CO2 occurring over shorter periods than the time to seal off. This is probably the cause of the near constant indicated CO2 composition over long periods.
The second issue arises from the comparison of levels and trends of CO2 made by other techniques. In particular, a set of measurements was made using the inverse relation between atmospheric carbon dioxide concentration and stomatal frequency in tree leaves to provide a method for detecting and quantifying century-scale carbon dioxide fluctuations (Wagner, F., Bohncke, S.J.P., Dilcher, D.L., Kurschner, W.M., van Geel, B. and Visscher, H. 1999. Century-scale shifts in early Holocene atmospheric CO2 concentration. Science 284: 1971-1973.). The results indicated CO2 levels varied considerably over the last several thousands years, and in some cases came much closer to present high levels than indicated in ice cores (to at least as high as ~348 ppm). In fact, a significant part of the difference between stomatal frequency based data and ice core data may be related to the first issue above.
The third issue relates to the CO2 content of trapped air being selectively reduced by dissolving in either a quasi-liquid or liquid layer. According to an article by John S. Wettlaufer and J. Greg Dashbears at:
“Ice has a quasi-liquid film, a natural state of solid ice formed by a process called surface melting, at temperatures down to near –40OC”. This layer has some structural characteristics of the solid below it but has the mobility and solubility of a fluid. This layer can contain dissolved gases such as CO2. In addition, there is the possibility of some liquid water being present in the ice even at temperatures below normal freezing. The rise in summer temperature and prolonged sunlight could even form melt layers (possibly subsurface) during glacier formation. When the melt liquid forms, the high solubility in the liquid could preferentially (compared to O2 and N2) take in a significant quantity of CO2. At release of pressure, when cores are drilled and raised, there could be some preferential CO2 loss from the micro cracks in the cores, or the ice could retain excess CO2 separate from the air bubbles.
Conclusions from the above are:
The process of the formation of glaciers may result in temporal smoothing of results on a time scale long enough to miss large level variations of CO2 lasting possibly hundreds of years.
Some alternate techniques that determine CO2 concentration over time contradict the slow changing ice record, but this may in fact be due to 1). This could mean present levels are not quite so extremely high or unusually fast changing as thought.
Quasi-liquid films and liquid water occurring during glacier formation could be a significant source of CO2 removal from trapped air bubbles, especially near the freezing point. Significant amounts of CO2 may preferentially dissolve even in a small amount of quasi-liquid or liquid. This could result in a preferential reduction of the CO2 concentration in the larger gas bubbles.
The final result is that there is some room for doubt for the reliability of ice core bubble composition to determine older CO2 concentrations in air, and a more reliable method to determine older CO2 atmospheric concentrations is badly needed.