The ultimate test for the IPCC's catastrophic AGW hypothesis is the existence of the predicted "hotspot" that is a sign of a positive feedback loop for accelerating global warming - newest data show that even after record setting human CO2 emissions the "hotspot" failed to materialize(click on image to enlarge - data sources)
Per the IPCC's global warming hypothesis, at the very top of the troposphere, above the equator region, is the location (12km, 200hPa @ 20°N - 20°S) that triggers a positive climate feedback, which produces the mythical runaway, tipping point of accelerated, dangerous global warming, which of course is unequivocal and irrefutable, except when it isn't.
This location is often referred to as the tropical "hotspot," supposedly an artifact of modern industrial/consumer human CO2 emissions.
The high climate sensitivity programmed into the IPCC's climate models is entirely dependent of this hotspot of positive feedback - with the hotspot, climate models predict a scary global warming range that spans from 2°C to 6°C.
If there is no tropical upper troposphere hotspot, then there is no positive feedback, and thus, no climate change crisis as predicted by the IPCC. If there is no hotspot, then the IPCC hypothesis of CO2 caused global warming (AGW) is essentially proven false.
Based on accepted physics, without the positive feedback triggered by the hotspot, surface global temperatures from a doubling of pre-industrial CO2 will increase by some +0.5° to 1.5°C. That is the range climate models predict (depending on the given climate model) if the "hotspot" does not exist.
The IPCC's gold-standard for upper troposphere data is the UK's HadAT2 dataset that represents high altitude balloon/radiosonde measurements. These balloons provide a higher resolution of the atmospheric layer temperatures than current satellites can provide. Over time, approximately 28+ million radiosonde measurements have taken place.
A few days ago (2/19/2013), the HadAT2 was finally updated through December 31, 2012 - the previous update of dataset was through 12/31/2011. The above chart plots the latest AT2 dataset and concurrent, well-mixed atmospheric CO2 levels over the last 17 years. (Why 17?)
Conclusions from the chart:
#1.The IPCC's tropical "hotspot" does not exist.
#2. Atmospheric CO2 levels over 350ppm do not cause a hotspot to occur.
#3. The climate sensitivity to CO2 is lower than expert assumptions.
#4. Temporary natural El Nino events do cause a spike in upper troposphere temperatures but then return to a lower temperature state (no positive feedback loop).
#5. The IPCC, its experts and climate models have been wrong about the mythical hotspot since the UN created the IPCC (1988).
#6. The continuing abysmal failure of climate models is likely associated with the lack of the mythical, hypothesized hotspot.
#7. The AGW hypothesis of tipping point, climate positive feedback is proven false after decades of zero empirical evidence supporting it.
#8. Despite all empirical evidence, IPCC scientists and bureaucrats will keep pushing the hotspot, positive feedback hypothesis in order to continue their lucrative taxpayer funding.
Recently, a new 2012 study by Stephen Po-Chedley and Qiang Fu found:
"It is demonstrated that even with historical SSTs as a boundary condition, most atmospheric models exhibit excessive tropical upper tropospheric warming relative to the lower-middle troposphere as compared with satellite-borne microwave sounding unit measurements. It is also shown that the results from CMIP5 coupled atmosphere–ocean GCMs are similar to findings from CMIP3 coupled GCMs. The apparent model-observational difference for tropical upper tropospheric warming represents an important problem..."
Previous studies have documented the tropical hotspot problem (source for all quotes here):
"Climate models and theoretical expectations have predicted that the upper troposphere should be warming faster than the surface. Surprisingly, direct temperature observations from radiosonde and satellite data have often not shown this expected trend." Sherwood et al 2008.
"On multi-decadal timescales, tropospheric amplification of surface warming is a robust feature of model simulations, but occurs in only one observational dataset." Other observations show weak or even negative amplification.” Santer et al 2005
“A recent report of the U.S. Climate Change Science Program (CCSP) identified a ‘potentially serious inconsistency’ between modelled and observed trends in tropical lapse rates.” Santer et al 2008
“Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs.” Douglass et al 2007
Update, per a reader's email: First, from the 2nd order draft of the IPCC's AR5, and second, from a comment at Judith Curry's 'Climate Etc.' blog:
"Section 184.108.40.206.2, p. 9-26, lines 31-33: "In Summary, there is a high confidence (robust evidence although only medium agreement) that most, though not all, CMIP3 and CMIP5 models overestimate the warming trend in the tropical troposphere during the satellite period 197902011. The cause of this bias remains elusive.""
"However my working hypothesis is that Santer would have continued to ignore these demonstrations, were it not for the Fu (2011, GRL) paper, which included Syukuro Manabe (godfather of CO2-climate modeling) as co-author also showing disagreement between models and measured temperatures...However, once the Fu 2011 paper came out, it became “establishment” that there was in fact a significant disagreement between models and measured temps. So now after the Fu 2011 paper we have (Thorne, 2011 [JGR], Po-Chedley (2012), Seidel (2012) and Santer (2012) all agreeing that models and measurements for tropical troposphere temperaures cannot be reconciled."
Note 1: A simple
hotspot explanation summarized from this article: Increasing CO2 levels causes atmosphere to warm;
then atmosphere causes Earth's surface to warm; warming of oceans cause
evaporation; increased evaporation leads to more water vapor in the
upper troposphere; water vapor is a powerful greenhouse gas that warms
the atmosphere even more (positive water vapor feedback); the Earth's surface warms
even more; and then auto 'repeat and rinse' until Earth's oceans boil, per an "expert."
Note 2: A scientist discusses the IPCC hotspot issue and dismantles a lame pro-hotspot argument (geesh, talk about alarmists' "scientific" mis-truths).
Note 3: The catastrophic global warming alarmists, be they "scientists" or political hacks, are very alarmed that the "hotspot" never materialized. To cover up this major failure of the AGW hypothesis, they usually attempt excited hand-waving to distract the gullible, including: the disingenuous, circular logic claim that it must exist because the models predict it, thus the measurements must be wrong; or the amazing claim that the hotspot exists but it just doesn't reveal itself to humans (really, trust us, it's hiding).