Long-Term Instrumental and Reconstructed Temperature Records Contradict Anthropogenic Global Warming

This paper analyses the monthly instrumental temperature records from 5 stations in the northern hemisphere, each of which are reliable, local and well over 200 years in length, as well as two reconstructed long-range yearly records – from a stalagmite near Innsbruck and from tree rings in the northern hemisphere that are about 2000 years long. In the instrumental records, the steepest fall in 100-year linear regression lines happened in the 19th century and the steepest rise in the 20th century, both events being of about the same magnitude. Evaluation by fluctuation analysis (FA) and detrended fluctuation analysis (DFA) revealed that both the 19th century fall and the 20th century rise have very small natural probabilities and must therefore be trends caused by external forcings. In contrast to this, the reconstructed records show far steeper 100-year rises and falls as quite common during the last 2000 years. Consequently, their DFA evaluation revealed far greater Hurst exponents. These results contradict the hypothesis of an unusual (anthropogenic) global warming during the 20th century. The cause of the different Hurst exponents for the instrumental and the reconstructed temperature records is not known. As a speculative hypothesis, the sun's magnetic field, which is correlated with sunspot numbers, could be put forward as an explanation. The long-term low-frequency fluctuations in sunspot numbers are not detectable by FA/DFA in the monthly instrumental records, resulting in low Hurst exponents. The same does not hold true for the 2000-year-long reconstructed records, which explains both their higher Hurst exponents and the higher probabilities of strong 100-year temperature fluctuations being quite common. A long-term synthetic record that embodies the reconstructed sunspot number fluctuations includes the different Hurst exponents of both the instrumental and the reconstructed records and, therefore, corroborates the conjecture.