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

TL;DR

This study compares long-term instrumental and reconstructed temperature records, finding that natural solar activity fluctuations, not human activity, better explain observed temperature variations over the past 2000 years.

Contribution

It introduces a hypothesis linking sun's magnetic field variations to long-term temperature fluctuations, challenging the mainstream view of anthropogenic global warming.

Findings

Instrumental records show 100-year temperature changes caused by external trends.

Reconstructed records reveal frequent 100-year temperature fluctuations over 2000 years.

Results suggest solar activity, not human influence, explains long-term temperature variability.

Abstract

Monthly instrumental temperature records from 5 stations in the northern hemisphere are analyzed, each of which is local and over 200 years in length, as well as two reconstructed long-range yearly records - from a stalagmite and from tree rings that are about 2000 years long. In the instrumental records, the steepest 100-year temperature fall happened in the 19th century and the steepest rise in the 20th century, both events being of about the same magnitude. Evaluation by the detrended fluctuation analysis (DFA) yields Hurst exponents that are in good agreement with the literature. DFA, Monte Carlo simulations, and synthetic records reveal that both 100-year events were caused by external trends. In contrast to this, the reconstructed records show stronger 100-year rises and falls as quite common during the last 2000 years. These results contradict the hypothesis of an unusual (anthropogenic) global warming during the 20th century. As a hypothesis, the sun's magnetic field, which is correlated with sunspot numbers, is put forward as an explanation. The long-term low-frequency fluctuations in sunspot numbers are not detectable by the DFA in the monthly instrumental records, resulting in the common 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. 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.