Trends in Extreme Weather Events since 1900 – An Enduring Conundrum for Wise Policy Advice

  • Date: 17/03/16
  • Michael Kelly, Journal of Geography and Natural Disasters

Abstract – It is widely promulgated and believed that human-caused global warming comes with increases in both the intensity and frequency of extreme weather events. A survey of official weather sites and the scientific literature provides strong evidence that the first half of the 20th century had more extreme weather than the second half, when anthropogenic global warming is claimed to have been mainly responsible for observed climate change. The disconnect between real-world historical data on the 100 years’ time scale and the current predictions provides a real conundrum when any engineer tries to make a professional assessment of the real future value of any infrastructure project which aims to mitigate or adapt to climate change. What is the appropriate basis on which to make judgements when theory and data are in such disagreement?


There have been many reports on the future impacts of human related greenhouse gas emissions on a changing climate during the 21st century. Just two will suffice here: ‘Resilience to Extreme Weather’ [1] and ‘Climate Change: Evidence and Causes’ [2] were both published in 2014 by the Royal Society of London, the second report jointly with the US National Academy of Science. Both reports dwell on the expectation that in future, because of man-made global warming, we can expect extremes of weather to be both more intense and more frequent. By implication, one must allocate vast sums of money in mitigating and adapting to this future of more extreme weather.

The members of the Intergovernmental Panel on Climate Change in Working Group I are clear that man-made global warming started in earnest in about 1960, so it is reasonable to see to what extent the weather has been getting more extreme more frequently over the last 55 years. That same report suggests that IPCC scientists have low confidence in recent extreme weather events being specifically attributed to global warming [3]. Further, an additional IPCC report on ‘Managing extreme events and disasters to advance climate change mitigation’, (known as SREX [4]), relies heavily on papers that only start with data in 1950 [5] and 1960 [6]. The graphical data is not shown in SREX, as it is here, but a one-phrase summary is incorporated. Furthermore, they chose definitions of extremes that represent the upper or lower deciles of occurrence, rather than treating extremes as extremes.

It is therefore surprising to discover that by all the various real world data considered here, the weather in the first half of the 20th century was, if anything, more extreme than in the second half. I have not found any data, including in SREX, that contradicts these trends. Furthermore there are no signs of this trend changing (i.e. lessening and reversing) in recent years. The lack of public, political and policymaker appreciation of the disconnect between empirical data and theoretical constructs is profoundly worrying, especially in terms of policy advice being given. For example the first report cited above is without empirical foundation, the second is misleading, and the already modest claims in SREX are further weakened when compared with the longer term data.

A comment on etymology is in order: I am using the word extreme in the same way that the authors of references [1,2] to mean events that are several standard deviations away from the average of the distribution by which they are measured and described. I am not referring to the ultimate extreme in recorded history, although these would also support my case.

The approach taken in this paper is wherever possible to list the original source research yielding the data, but where that is not available to use the earliest accessible details. Not all the relevant data is located in the regular scientific literature. Much of this data is on official government-backed meteorological websites, while other data is only available secondarily or appears in appropriately derived form in various web-sites devoted to critiques in the global warming debate. To my knowledge, this material has not before been gathered systematically in the manner it has here. By referring to a much broader base than temperature data only, I hope to avoid the continuing debate on the myriad of adjustments made to original data that has almost without exception exacerbated the trends being sought, particularly in rising temperature over the 20th century. These adjustments are such that in some places (e.g. New Zealand) the inferred temperature rise is entirely a result of these post-hoc adjustments.

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