Feature image: 2017 average temperature departure from long-term average (1981-2010) (https://www.nasa.gov/sites/default/files/atoms/files/noaa-nasa-global_analysis-2017.pdf).
Original article: Mudelsee, M. 2019. Trend analysis of climate time series: A review of methods. Earth-Science Reviews 190:310-322. https://doi.org/10.1016/j.earscirev.2018.12.005
THE HOCKEY STICK AND CLIMATE SCIENCE
In 1998, Michael Mann and his co-authors published a now-classic paper in Nature revealing gradual cooling starting around 1400 with a sharp rise in temperature in the 20thcentury. The graph resembled a hockey stick, becoming the icon for global warming. This temperature pattern has been confirmed many times since then, with data from thermometers and satellites, melting glaciers, ice-out in lakes in cold regions, and other data sources associated with temperature (so-called climate proxies).
Climate scientists continue to test the hockey-stick pattern of global warming with enhanced data and better statistical techniques. Moreover, every year, new data stream in about our changing Earth. In a recent paper in Earth Science Reviews, Dr. Manfred Mudelsee, a climatologist in Germany, provides a revealing update on those efforts.
WHY IS THIS PAPER IMPORTANT?
Despite the incontrovertible science behind rising global temperatures, climate change deniers have attacked the hockey stick pattern since its publication. As corroboration of 20thcentury warming has piled up, criticism has submerged under media coverage of rapid environmental change, but it nonetheless persists. In 2010, for example, Andrew Montford published the Hockey Stick Illusion, and climate change denial continues to be a talking point for many powerful politicians.
Most climate change deniers no longer argue with 20thcentury global warming, but instead claim that temperatures stopped rising after 1998—a so-called “global warming hiatus.” The argument goes that earlier warming must have been a natural fluctuation since the planet then ceased to warm despite continued human-caused carbon emissions and increased atmospheric carbon dioxide concentrations. So, there’s little for us to worry about! If only that were true.
Global average annual temperature (1880-2017) from NASA Goddard Institute for Space Studies.
WHAT DOES THE NEW ANALYSIS REVEAL?
This new article—written for a broader audience than most climate science papers— summarizes the different ways that global temperatures can be analyzed to assess patterns of past warming. It uses one of the best temperature data sets: a land surface and ocean record collected by the NASA Goddard Institute for Space Studies. Analyzing this time series through 2017 with the most current statistical methods, Mudelsee shows unequivocally that the “global warming hiatus” does not exist, a conclusion that is also supported by earlier studies. The author also sheds light on other anomalies in the temperature record, such as the unusually high temperatures during WWII, which may be the result of changes in methods for measuring temperature.
One of the most profound conclusions of the article is that “selection of the fit interval for trend estimation—has also a moral aspect. Climate researchers should be aware of this.” In other words, climate data analysis can be manipulated in ways to ensure a certain outcome. That’s why the rigorous peer-review process to which mainstream climate science is subject is so essential to revealing the stark reality of climate change.
IPCC. 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
IPCC. 2018. Summary for Policymakers. In: Global warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty[V. Masson-Delmotte, P. Zhai, H. O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J. B. R. Matthews, Y. Chen, X. Zhou, M. I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, T. Waterfield (eds.)]. World Meteorological Organization, Geneva, Switzerland, 32 pp.