Does last century warming exceed natural variations?

Dr. Philip Loyd from South-Africa has published in Energy & Environment a short but easily understandable paper trying to ask this question (link to abstract). He took several reconstructed temperature series reaching back up to over 8000 years, i.e. covering the Holocene period. An example shown in the figure below is the Gips-2 reconstruction from a Greenland ice core, where temperatures have been deduced from an analysis of the Ar (Argon) and N2 (Nitrogen) isotopes.

First he de-trended the data by subtracting the best polynomial fit (which was a linear one in this case); than he calculated the differences from temperatures 100 years apart, and finally calculated the statistical standard deviation of this ensemble. The following figure gives the result for the 4 series that he used:

Taking these 4 results and computing the average gives 0.98 (rounded to 2 decimals) with an uncertainty of 0.27.

So the historical data show that temperatures fluctuate naturally by ~0.98 °C during one century; as the Hadcrut3 series for global temperatures from 1900 to 1999 gives a warming of 0.7°C, this number is smaller than the natural centennial variability. The author concludes prudently “the signal of anthropogenic global warming may not yet have emerged from the natural background”; which means in very simple words that human caused centennial warming (by greenhouse gas emissions for instance), if it exists, does not exceed for the moment natural temperature variability.

The most controversial points in climate science

Prof. Judith Curry (GeorgiaTech) has a very interesting comment in here outstanding blog Climate Etc.

A journalists asked her “What are the most controversial points in climate science related to AGW (anthropogenic global warming)?”
Prof. Curry gives two very simple, easy understandable answers:

1. Has the warming since 1950 been dominated by human causes?
2. How much will the planet warm during the 21th century?

The IPCC continues to ignore the importance of natural causes for climate change (and global warming), putting as an act of faith that nearly all changes are caused by human activity. Some dubious graphs appeared in the AR’s and others showed that only when climate models take account of green house gas emissions (actually of atmospheric CO2 mixing ratio), observations and models become compatible:

(“Climate Change Attribution” by Robert A. Rohde)

This figure ignores the fudge factors (=parameters) introduced in the models until their result becomes similar to the observations. This technique is more related to curve fitting than to an understanding of all the physical causes of the observed temperature variation.

The insufficient understanding of the natural causes of climate change remains the major obstacle for believing the IPCC so-called “consensus”. We are still largely ignorant about the magnitude (and possibly even the sign) of the influence of factors as cloud cover, solar variation (total irradiance, UV changes, possible amplification of small natural changes). What we are sure is that the climate models overstate enormously the observed global temperature increase during the last 15 to 18 years (read this comment by Fyfe et al.):

This figure (link) documents clearly that climate models should not be used as a basis for political decisions: the green curve represents the global temperature anomaly according to Hadcrut4 (land and ocean based weather stations) and UAH (satellite data) up to 2013. It is remarkable how far the different models deviate from one another: the enormity of the differences makes the suggestion that the average ( the black line) somehow represents the “truth” absolutely questionable. Are our political deciders aware of  this?