Guest post by David Middleton
The hyping of Lovejoy, 2014 (L14) has been almost as unprecedented as his conclusions are unsupported…
Lovejoy piles on with the sort of trash talk normally associated with activist bloggers, rather than professional scientific publications…
“This study will be a blow to any remaining climate-change deniers,” Lovejoy says. “Their two most convincing arguments – that the warming is natural in origin, and that the computer models are wrong – are either directly contradicted by this analysis, or simply do not apply to it.”
Lovejoy’s “analysis” addresses neither the natural variability of the Late Holocene climate, nor the abject failure of the computer models. That said, Lovejoy does deserve credit for trying an empirical approach, independent of models and at least paying lip service to natural variability. However, L14 is seriously flawed in at least three ways:
- Nothing in Earth Science is 99% certain.
- A fundamental misunderstanding of Holocene climate variability.
- A totally unscientific and [demonstrably] wrong assessment of equilibrium climate sensitivity.
99%? Give me a break!
While I have no doubt that the Earth’s average surface temperature is a bit higher now than it was in the 1800’s, this cannot be asserted at 95%, much less 99% confidence.
Quasi-periodic fluctuations aren’t necessarily stochastic processes
Climate change is cyclical. If it wasn’t cyclical, sequence stratigraphy wouldn’t exist. So, anyone who insists that climate cycles aren’t true oscillations, please pretend that I am using the phrase, “quasi-periodic fluctuations” rather than cycles or oscillations. L14 totally fails to evaluate modern warming within the context of natural variability, largely due to the assumption that it must be stochastic in order to be natural…
Lovejoy’s assumption is that all of the secular-ish warming in the instrumental record is anthropogenic.
L14 totally fails to evaluate the instrumental era warming within the context of natural climate variability. What was the climate doing before 1880? Just about the same thing it has been doing since 1880…
Pretty well all of the [spectrally] consistent (non-hockey stick) reconstructions yield the same conclusion…
If we take Moberg and Ljungqvist back to the year zero, we can clearly see another characteristic of the Late Holocene climate: A millennial scale cycle with a period of ~1,000 years and amplitude of ~0.5 °C.
These cycles even have names…
These cycles have been long recognized by Quaternary geologists…
Fourier analysis of the GISP2 ice core clearly demonstrates that the millennial scale climate cycle is the dominant signal in the Holocene (Davis & Bohling, 2001). It is pervasive throughout the Holocene (Bond et al., 1997).
The industrial era climate has not changed in any manner inconsistent with the well-established natural millennial scale cycle. Assuming that the ice core CO2 is reliable, the modern rise in CO2 has had little, if any effect on climate…
While the climate may have warmed by 0.2 to 0.4 °C more than what might be expected to occur in a 100% natural warming phase of the millennial cycle, all of the apparent excess warming may very well be due to resolution differences between the instrumental and proxy data…
According to Ljungqvist…
The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. AD 1-300, reaching up to the 1961-1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300-800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300-1900, followed by a rapid temperature increase in the twentieth century. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961-1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself.
The proxy reconstruction itself does not show such an unprecedented warming but we must consider that only a few records used in the reconstruction extend into the 1990s. Nevertheless, a very cautious interpretation of the level of warmth since AD 1990 compared to that of the peak warming during the Roman Warm Period and the Medieval Warm Period is strongly suggested.
The amplitude of the temperature variability on multi-decadal to centennial time-scales reconstructed here should presumably be considered to be the minimum of the true variability on those time-scales.
Ljungqvist is recommending caution in comparing the modern instrumental record to the older proxy reconstructions because the proxy data are of much lower resolution. The proxy data are showing the “minimum of the true variability on those time-scales.” The instrumental data are depicting something closer to actual variability. Even then, the instrumental record doesn’t exceed the margin of error for the proxy data during the peak of the Medieval Warm Period. With a great deal of confidence, perhaps even 67%, it can be concluded that at least half, perhaps all, of the modern warming is the result of quasi-periodic natural climate fluctuations (AKA cycles).
Lovejoy’s 99% conclusion is consistent with climate sensitivities demonstrated to be overwhelmingly wrong
I won’t bother with Lovejoy’s references to Arrhenius, Lord Monckton has already dealt very nicely with that fallacy (as did Angstrom about 5 minutes after Arrhenius discovered AGW). I’ll just get right to his supposedly empirical estimate of equilibrium climate sensitivity…
Our good friend, James Hansen, ruled out 4.5 K back in 1988..
~3.0 K hasn’t worked out so well either…
All of the recent observation-derived climate sensitivity estimates put the total warming due to a doubling of atmospheric CO2 between 0.5 and 2.0 °C.
- Spencer & Braswell,2010, 2011 and Lindzen & Choi, 2009, 2011 came up with a likely ECS in the range of 0.5 to 0.6 °C.
- Asten, 2012 found ECS to be 1.1 ± 0.4 °C based on δ18O and δ11B records from fossil forams and the Eocene-Oligocene transition in marine sediment cores from DSDP site 744.
- Researchers at CICERO and the Norwegian Computing Center announced that when they incorporated the temperature and CO2 data from 2000-2010 into their instrumental record-based ECS estimate, they obtain a most likely value of 1.9 °C.
- Lewis, 2013 found a most likely ECS of 1.6 K using a Bayesian analysis and incorporating recent data.
- Masters, 2013 found a most likely ECS of 1.98 K from ocean heat content and sea surface temperature data.
- Aldrin et al, 2012 and Forster & Gregory, 2006 also found the ECS to most likely be less than 2 °C.
If I cross plot the high resolution DE-08 ice core from Law Dome, Antarctica against Moberg, I get an ECS of about 1.9 °C with a fairly good correlation. The earlier (deeper and lower resolution) ice cores are poorly correlated with temperatures at millennial scale resolution (see this post for more details).
However, this assumes that all of the warming is anthropogenic… At least half of the warming is highly likely to be natural, yielding an ECS of about 1 °C (the assumed radiative forcing with neutral feedbacks). If at least half of the rise in CO2 is natural, as demonstrated by plant stomata, then the total anthropogenic component is about 0.5 °C. There simply is no scientific basis to predict more than 2 °C of global warming from a doubling of atmospheric CO2 (280 to 560 ppmv). Therefore there is no scientific basis to forecast any effects from more than 2 °C of warming…
Lovejoy’s 99% solution fails to quantify or even accurately describe the patterns of natural variability of the Late Holocene climate. Therefore, his conclusion that the warming since 1880 (~0.4 °C per century) cannot be natural is unsupported in his analysis. While it is possible that up.to half of the industrial era warming might be due to the rise in the atmospheric CO2 concentration, this is hardly conclusive and certainly not at 95% confidence, much less 99%. Davis and Bohling demonstrated that 140-yr runs of 0.4 °C per century runs of warming and cooling were not unusual in the GISP2 ice core. The fact that the industrial era slope is roughly twice the norm of the past 2,000 years does not prove that it is of anthropogenic origin. The Little Ice Age was quite possibly the coldest phase of the Holocene since the 8.2 KYA Cooling Event. The LIA was characterized by maximum glacial advances and the most extensive sea ice coverage since the onset of the Neoglaciation (end of the Holocene Climatic Optimum).
While volcanic forcing may have played a role in the coldness of the LIA, it was clearly a.cyclical cooling event. Much, if not all, of the warming since the late 16th century is clearly part of a millennial climate cycle. This cycle evident in Greenland ice cores throughout the Holocene interglacial and the last Pleistocene glacial stages…
All of the “global warming” from ~1600 AD through 2000 AD barely brought the climate back to “normal.”
I have intentionally not addressed the causes, drivers and/or forcing mechanisms of the millennial scale cycle. My goal here was to describe and quantify how the Holocene climate was behaving prior to the industrial era. Geologists tend to try to figure out what happened before trying to draw conclusions about why it happened. I have a hunch that Henrik Svensmark is on the right track and that the Sun, the stars and cyclical variations in cloud cover and albedo are the answer. Only time will tell.
- Alley, R.B. 2000. The Younger Dryas cold interval as viewed from central Greenland. Quaternary Science Reviews 19:213-226.
- Bond, G., W.Showers, M.Cheseby, R.Lotti, P.Almasi, P.deMenocal, P.Priore, H.Cullen, I. Hajdas, and G. Bonani, A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates, Science, 278, 12571266, 1997.
- Davis, J. C., and G. C. Bohling, The search for patterns in ice-core temperature curves, 2001, in L. C. Gerhard, W. E. Harrison, and B. M. Hanson, eds., Geological perspectives of global climate change, p. 213–229.
- GISP2 Ice Core Temperature and Accumulation Data. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2004-013. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.
- Grosjean, M., Suter, P. J., Trachsel, M. and Wanner, H. 2007. Ice-borne prehistoric finds in the Swiss Alps reflect Holocene glacier fluctuations. J. Quaternary Sci.,Vol. 22 pp. 203–207. ISSN 0267-8179.
- Hansen, J., I. Fung, A. Lacis, D. Rind, Lebedeff, R. Ruedy, G. Russell, and P. Stone, 1988: Global climate changes as forecast by Goddard Institute for Space Studies three-dimensional model. J. Geophys. Res., 93, 9341-9364, doi:10.1029/88JD00231.
- Ljungqvist, F.C. 2009. N. Hemisphere Extra-Tropics 2,000yr Decadal Temperature Reconstruction. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series # 2010-089. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA.
- Ljungqvist, F.C. 2010. A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia. Geografiska Annaler: Physical Geography, Vol. 92 A(3), pp. 339-351, September 2010. DOI: 10.1111/j.1468-459.2010.00399.x
- Lovejoy, S., 2014: Scaling fluctuation analysis and statistical hypothesis testing of anthropogenic warming, Climate Dyn. DOI 10.1007/s00382-014-2128-2.
- MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins. 2006. The Law Dome CO2, CH4 and N2O Ice Core Records Extended to 2000 years BP. Geophysical Research Letters, Vol. 33, No. 14, L14810 10.1029/2006GL026152.
- Moberg, A., D.M. Sonechkin, K. Holmgren, N.M. Datsenko and W. Karlén. 2005. Highly variable Northern Hemisphere temperatures reconstructed from low-and high-resolution proxy data. Nature, Vol. 433, No. 7026, pp. 613-617, 10 February 2005.
- Instrumental Temperature Data from Hadley Centre / UEA CRU, NASA Goddard Institute for Space Studies and Berkeley Earth Surface Temperature Project via Wood for Trees.