The United Nations is misusing statistics to try and prove a causal relationship between the reported increase in carbon dioxide concentrations and the purported increase in extreme hurricane events over the last several decades, focusing in particular on the 2017 Atlantic hurricane season. “Over the past 30 years, the number of annual weather-related disasters has nearly tripled, and economic losses have quintupled,” UN Secretary General Antonio Guterres said at a press briefing on Wednesday. To “prove” his point, graphs were distributed to reporters that show carbon dioxide concentration levels and ocean temperatures rising since 1960, together with an increase in the number of meteorological natural disasters. “Scientists are learning more and more about the links between climate change and extreme weather,” the Secretary General added. He then predictably called for “countries to implement the Paris Agreement [on climate change], and with greater ambition.”
The UN is using the familiar logical fallacy of equating statistical correlations with proof of causation. The National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory issued a report, last revised on August 30, 2017, that demonstrates the crucial difference between mere statistical correlation and proof of causation. The report found that “records of Atlantic hurricane activity show some correlation, on multi-year time-scales, between local tropical Atlantic sea surface temperatures (SSTs) and the Power Dissipation Index (PDI),” which is “an aggregate measure of Atlantic hurricane activity.” However, the report went on to conclude that it is “premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming–have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity.” Computer models may indeed predict increased storm intensity and destruction by the end of this century based on some measures of historical data showing increases in sea surface temperatures. However, the extent to which this would be due to an increase in 21st century greenhouse warming caused by human activity is indeterminate at the present time.
Moreover, even the statistical correlations may be misleading. The report examined records of past Atlantic tropical storm or hurricane numbers (1878 to present), which it found to be incomplete in terms of reported storms prior to 1965. Reliance on ship-based observations during that period meant that some storms, particularly short-lived ones, were simply overlooked because they had less opportunity for chance encounters with ship traffic. There were no satellites more than five decades ago to observe and measure hurricanes with the same degree of accuracy as can be performed today. Even with the sketchier information we do have regarding hurricanes in the latter part of the nineteenth century and the early part of the twentieth century, we know that five of the eight seasons with the most major hurricanes since 1851 occurred prior to 1965. The strongest hurricane on record to hit the U.S. occurred on the Florida Keys on Sept. 2, 1935. And while Hurricane Maria was a tragically devastating hurricane to be sure, Puerto Rico suffered an even worse hurricane in 1928.