Friday, November 25th 2011, 1:01 PM EST
Fig 1. The modern satellite temperature record first became available from 1979.
On the face of it there was a decline throughout the period, but look more closely. A decline from 1979 to about 1994 and then flat. The two spikes around 1983 and 1993 were a consequence of volcanic eruptions injecting material into the stratosphere resulting in short term warming of the lower stratosphere. They do not appear to affect the background trend.
That decline has been taken as evidence in support of the proposed effect of human CO2 emissions because more greenhouse gases are supposed to hold energy in the troposphere for longer thus cooling the stratosphere.
However, human CO2 emissions have been increasing faster than ever since 1994 so why would the cooling stratospheric temperature trend have stopped? The observations do not fit the theory that CO2 quantities were the cause of that period of stratospheric cooling.
Obviously some other factor is in play.
Fig 2. The modern satellite temperature record first became available from 1979.
On the face of it there was an increase throughout the period but look more closely. An increase from 1979 to about 2000 and then flat. The spikes around 1998 and 2010 were a consequence of strong El Nino events releasing oceanic warmth to the air resulting in short term warming of the troposphere. They do not appear to affect the background trend.
On the basis of the above two charts it seems that the global background trend in stratosphere and troposphere is not significantly affected by volcanic events or individual El Nino events.
It is also clear that the temperature trends in the lower stratosphere and the lower troposphere are mirror images of one another. They appear to move in opposite directions despite short term disruption from volcanic events or El Nino events.
The difference in the average slope is probably related to the density differences. It will require more of an energy content change to alter the gradient in the troposphere because of the greater density of the troposphere. Thus for any given change in atmospheric energy content the slope in the troposphere will change less than the slope in the stratosphere.
The fact that the change in background trend to flat occurred in the stratosphere a few years before the change in background trend to flat in the troposphere is probably due to the thermal inertia of the oceans.
Fig 3. 1987 was the year when such information first became available.
Interestingly one can see subdued versions of the 1993 volcanic spike and the El Nino spikes of 1998 and 2010 but again they are short term effects only and do not alter the flat background trend.
The trend is clearly flat throughout which demonstrates that the opposing trends in the stratosphere and troposphere cancel out at the tropopause or possibly (over a longer period) leave a tiny positive or negative residue which is indicative of net system warming or net system cooling at any given time. For the period 1987 to date there appears to be a very small decline which suggests to me that any increase early in the period has been slightly more than offset by a small decrease over the past 12 years or so. It is generally accepted that there has been little or no tropospheric warming over the past 12 years despite an increase in human CO2 emissions.
I suggest that a positive or negative change in the TTS represents a change in the average height of the tropopause at the latitude where the data is recorded and it is that change which represents a change in the rate of energy flow through the Earth system AND a shift in the surface latitudinal positions of the climate zones which we perceive as climate change.
That change in the rate of energy flow through the Earth system serves to keep the Earth system energy content at equilibrium despite changes in solar input or changes in greenhouse gas quantities.
4) The only reasonable conclusion to be drawn from the above is that CO2, volcanic outbreaks and El Nino events have little or no effect on the background temperature trends in stratosphere and troposphere because of the ability of the Earth system to change the height of the tropopause and the size and location of the permanent climate zones to change the speed of energy flow through the Earth system and thereby negate any such effects. The TTS data shows almost a zero change from 1987 to 2011. We have to look elsewhere for the cause of the change in temperature trend to flat in BOTH stratosphere and troposphere that occurred in the middle and late 1990s.
The only change that fits is the decline in solar activity from the peak of solar cycle 23.
5) I have already proposed a mechanism whereby this observed outcome could be achieved as a result of solar variability:
[UPDATED with new link] Click this link from ClimateRealists.com.com to read How The Sun Could Control Earth's Temperature...for a description of how the observed opposite temperature trends in stratosphere and troposphere could be achieved without the need to invoke any significant CO2 effect.
That is the only climate description that I am aware of that accommodates the observed opposite temperature trends in stratosphere and troposphere as a result of solar variability.
and, note also:
Click this link from ClimateRealists.com to download PDF file The Setting and Maintaining of Earth's Equilibrium Temperature...for a description of the influence of the oceans in setting the energy content of the entire Earth system.
and, how it all fits together:
Click this link from ClimateRealists.com to download PDF fileThe Unifying Theory of Earth's Climate...for a description of how variability in the size and speed of the water cycle and of the positions, sizes and intensities of the permanent climate zones work together to alter the rate of energy flow from surface to space to maintain Earth system stability.
Whether or not the current flat global tropospheric temperature trend turns to cooling or back to warming will most likely depend on what the sun does next. So far, the less active sun has merely caused the tropospheric warming trend to cease. A continuation of solar inactivity should turn that into a decline if it lasts long enough.
We are still not back to the warmth of the MWP or the Roman Warm Period so it seems a bit early to be on a long term downtrend just yet.