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?