by Leonard Weinstein, ScD, April 25, 2009, Google
A hypothesis has been proposed that human activity over about the last 150 years has caused a significant rise in Earth’s average temperature.
The mechanism claimed is based on an increased greenhouse effect caused by anthropogenic increases in CO2 from burning of fossil fuels, deforestation, cement manufacture, and also from increases in CH4 from farm animals and other causes.
The present versions of the hypothesis also include a positive feedback effect due to the increased temperature causing an increase in water vapor, which amplifies the effect. The combined result is used to claim that unless anthropogenic increases of CO2 are slowed down or even made to decrease, there will be a continuing rapid increase in global temperature, massive melting of ice caps, flooding, pestilence, etc.
In order to support a hypothesis, specific predictions need to be made that are based on the claims of the hypothesis, and the predictions then need to either happen or be falsified. While the occurrence of the predicted events is not proof positive of a hypothesis, they increase the believability of the claims. However, if the predictions are not observed, this tends to indicate the hypothesis is flawed or even wrong. Some predictions are absolute in nature. Einstein’s prediction of the bending of light by the Sun is such a case. It either would or would not bend, and this was considered a critical test of the validity of his hypothesis of general relativity. It did bend the predicted amount, and helped raise the concept to the status of theory.
Many predictions however are less easily supported. For example, weather forecasting often does a good job in the very short term but over increasing time does a poor job. This is due to the complexity of the numerous nonlinear components. This complexity has been described in chaos theory by what is called the butterfly effect. Any effect that depends on numerous factors, some of which are nonlinear in effect, is nearly impossible to use to make long-range predictions.
However, for some reason, the present predictions of “Climate Change” are considered by the AGW supporters to be more reliable than even short-term weather forecasting. While some overall trends can be reasonably made based on looking at past historical trends, and some computational models can suggest some trends due to specific forcing factors, like any respectable hypothesis, specific predictions need to be made, and then shown to happen, before the AGW models can have any claim to being reasonably valid.
The AGW computational models do make several specific predictions. Since the time scale for checking the result of the predictions is small, and since local weather can vary enough on the short time scale to confuse the longer time scale prediction, allowances for these shorter lasting events have to be made when examining data that is supposed to be supporting the predictions. Nevertheless, if the actual data results do not significantly support the stated predictions, the AGW hypothesis must be reconsidered or even rejected as it stands.
The main predictions from the AGW models are:
- The average Earth’s temperature will increase at a rate of 0.20C to 0.60C per decade at least to 2100, and will continue to climb after that if the CO2 continues to be produced by human activity at current predicted rates.
- The increasing temperature will cause increased atmospheric water vapor content, which is the cause for the positive feedback needed to reach the high temperatures.
- The relative temperatures at lower latitudes (especially tropical regions) will increase significantly more in the upper Troposphere than near the surface.
- The greatest near surface temperature increases will occur at the higher latitudes.
- The increasing temperature at higher latitudes will cause significant Antarctic and Greenland ice melt. These combined with ocean expansion due to warming will cause significant ocean rise and flooding.
- A temperature drop in the lower Stratosphere will accompany the temperature increase near the surface. The shape of the trend down in the Stratosphere should be close to a mirror reflection of the near surface trend up.
The present CO2 level is high and increasing (See Trends in Atmospheric Carbon Dioxide). It should be fairly easy to show the consequences of AGW predictions if they are valid.
Figure 1. Global average temperature from 1850 through 2008. Annual series smoothed with a 21-point binomial filter by the Met Office.
It should be noted that the largest part of the last 150 year increase in CO2, which is blamed on human activity, did not occur until after 1940, so the largest temperature rise effects should have occurred in that time period. The proponents of AGW have generally used the time period from 1970 to 2000 as the base line for an indicator of the rapid warming. In that base line period, the average temperature rose about 0.50C, which averages to 0.160C per decade. The claim was then made that this would accelerate due to continuing increases in CO2 level.
However if we look at the temperature change from 1940 through 2008, the net increase is only 0.30C. This is due to a drop from 1940 to 1970 and a slight drop from 2000 through 2008. Now the average rise for that period is only 0.040C per decade. If the time period from 1850 through 2008 is used as a base, the net increase is just under 0.70C and the average rise is also 0.040C per decade.
It is clear that choosing a short selected period of rising temperature gives a misleading result. It is also true that the present trend is down and expected to continue downward for several more years before reversing again. This certainly makes claim 1 questionable.
The drop in temperature from 1940 to 1970 was claimed to have been caused by “global dimming” caused by aerosols made by human activity. This was stated as dominating the AGW effects at that time. This was supposed to have been overcome by activity initiated by the clean air act.
In fact, the “global dimming” continued into the mid 1990’s and then only reduced slightly before increasing more (probably due to China and other countries increased activity). If the global dimming was not significantly reduced, why did the temperature increase from 1970 to just past 2000?
In addition, the absolute atmospheric water vapor content has also not increased at the altitudes predicted for feedback. The lack of increase in water vapor content increase falsifies claim 2.
Claim 3 has been falsified by a combination of satellite and airborne sensor measurements.
While the lower Troposphere average temperature has generally risen along with near ground air temperature, nevertheless the models predicted the upper Troposphere increase would be significantly greater than near ground at the lower latitudes, especially in the tropics. This has not occurred.
The following statement from:Synthesis and Assessment Product 1.1 Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research April 2006
“While these data are consistent with the results from climate models at the global scale, discrepancies in the tropics remain to be resolved.”
does not sound like a big issue, but in fact it is the issue with claim 3. Both the direct measured and satellite data show that the atmospheric relative hot spot required from the models is missing. This falsifies claim 3.
Claim 4 implies that the higher latitudes should heat up more than lower latitudes.
This is supposed to be especially important for melting of glaciers and permafrost. In fact, Antarctica has overall cooled much of the last 50 years except for the small tail that sticks out. See: Robust Verification Statistics, Antarctic Temperature Changes, and Earth Observation.
This is now claimed to be due to the Ozone hole effect. The Arctic sea region and Greenland have warmed rapidly between 1960 and 2000, but they were actually about as warm or warmer in the late 1930’s, and are presently cooling. See The Truth About Arctic and Greenland Ice.
This appears to falsify claim 4, although it may be too early to be sure.
The overall ice volume balance of the land portions of Antarctic and Greenland are presently resulting in near zero net gain of ice, not significant loss. While some small areas have recently lost and are some are still losing some ice, this is mostly sea ice and thus do not contribute to sea level rise.
Glaciers in other locations such as Alaska have lost a significant amount of ice in the last 150 years, but much of the loss is from glaciers that formed or increased during the little ice age, or from local variations, not global. Most of this little ice age ice is gone and some glaciers are actually starting to increase as the temperature is presently dropping. For more discussions on the sea level issue look at the following two sites:
These facts and analysis seem to falsify claim 5.
While sea level may rise a small amount, and has so since the start of the Holocene period, the rise is now only 10 to 15 cm per century, and is not significantly related to the recent recovery from the little ice age, including the present period of warming.
The claims in 6 are particularly interesting.
Figure 2 below shows the Global Brightness Temperature Anomaly (0C) in the lower Troposphere and lower Stratosphere made from space.
a) Channel TLT is the lower Troposphere from ground to about 5 km
b) Channel TLS is the lower Stratosphere from about 12 to 25 km
Figure 2. Global satellite data from RSS/MSU and AMSU data. Monthly time series of brightness temperature anomaly for channels TLT, and TLS.
The anomaly time series is dominated by ENSO events and slow troposphere warming for Channel TLT (Lower Troposphere). The three primary El Niños during the past 20 years are clearly evident as peaks in the time series occurring during 1982-83, 1987-88, and 1997-98, with the 1997-98 being the largest. It also appears there is an additional one at 2007.
Channel TLS (Lower Stratosphere) is dominated by stratospheric cooling, punctuated by dramatic warming events caused by the eruptions of El Chichon (1982) and Mt Pinatubo (1991). In these, and other volcanic eruption cases, the increased absorption and reflectivity of the dust and aerosols at high altitudes lowered the surface Solar insolation, but since they absorbed more energy, they increased the high altitude temperature.
After the large spikes dropped back down, the new levels were lower and nearly flat between large volcanic eruptions. It is also likely that the reflection or absorption due to particulates also dropped, so the surface Solar insolation went back up.
It appears that a secondary effect of the volcanic eruptions is present that is unknown in nature (but not CO2). One possible explanation is a modest but long-term drop in Ozone triggered by the volcanoes.
It is also clear that the linear fit to the data shown is meaningless.
In fact, the level drop events seem to be additive if they overlap soon enough. That is, after El Chicon dropped the level, then Pinatubo occurred and dropped the level even more. Two months after Pinatubo, another strong volcano, Cerro Hudson, also erupted, possibly amplifying the effect. It appears that the recovery time from whatever causes the very slow changing level shift has a recovery time constant of at least several decades.
The computational models that show increasing CO2 and CH4 cause most of the present global warming all require that the temperature of the Stratosphere drops while the lower atmosphere and ground heat up.
It appears from the above figures that the volcanic activity clearly caused the temperature to spike up in the Stratosphere, and that these spikes were immediately followed by a drop to a new nearly constant level in the temperature.
It is clear from the Mauna Loa CO2 data Trends in Atmospheric Carbon Dioxide that the input of CO2 (or CH4) from the volcanoes, did not significantly increase the background level of this gas, and thus, this cannot be the cause of the drop in the Stratosphere temperature.
The ramp up of atmospheric CO2 also cannot explain the step down then level changes in high altitude temperature. Since the surface temperature rise is supposed to be related to the Stratosphere temperature drop, and since a significant surface rise above the 1940 temperature level did not occur until the early 1980’s, it may be that the combination of the two (or more) volcanoes, along with Solar variability and variations in ocean currents (i.e., PDO) may explain the major causes of recent surface temperature rises to about 2002.
In fact, the average Earth temperature stopped rising after 2002, and has been dropping for the last few years. While this somewhat confusing result data does not clearly falsify the claim 6, it also does not support it.
The final question is what prediction has the AGW hypothesis made that has been demonstrated, and that strongly supports the hypothesis. It appears that there is NO real supporting evidence and much falsifying evidence for the AGW hypothesis as proposed. That is not to say there is no effect from Human activity. Clearly human pollution (not greenhouse gases) is a problem. There is also very likely some contribution to the present temperature variations from the increase in CO2 and CH4, but it is almost certainly a small effect and not a driver of future climate.
Any reasonable scientific analysis must conclude the basic AGW hypothesis fails.