Climate at a Glance: Floods

A flooded intersection in Baton Rouge, LA, on August 14, 2016. Twitter image by the Louisiana Department of Transportation and Development.

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Key Takeaways:

  • The U.N. Intergovernmental Panel on Climate Change (IPCC) reports it has “low confidence” climate change is impacting flooding.
  • The U.N. IPCC admits having “low confidence” in even the “sign” of any changes—in other words, it is just as likely that climate change is making floods less frequent and less severe.1
  • Studies of rivers and streams that have not been altered by human development show very little, if any, increase in flooding events.
  • Floods always have and always will occur. With no increase in overall flooding activity, there is no justifiable reason to blame any recent, current, or near-future flooding event on climate change.

Short Summary:

Occasional heavy precipitation events and floods have always occurred and always will. The IPCC reports it has “low confidence” climate change has had a measurable impact on flooding. Moreover, IPCC acknowledges that climate change is as likely to have reduced flooding as it is to have made flooding events more common. When climate activists point to a particular flooding event and claim climate change is to blame, the assertion defies objective data and even the IPCC’s own analyses.

Predictions of future flooding are merely that, speculative predictions. Those who claim flooding events could increase in the future do so in contradiction to real-world data. Additionally, if any increase in flooding were to occur in the near future, that increase would need to be considered alongside real-world reductions in drought reported by the U.S. National Oceanic and Atmospheric Administration (NOAA).

As Figure 1 shows, NOAA has documented a significant reduction in the costs associated with flooding in the United States over the past century. In the 2018 National Climate Assessment published by NOAA, it is stated on page 99, “Human-induced warming has not been formally identified as a factor in increased riverine flooding and the timing of any emergence of a future detectable human caused change is unclear.”

Figure 1. Annual Cost of U.S. Flood Damage, 1903–2019

Figure 1. U.S. flood damage as a proportion of U.S. gross domestic product. Data plotted by Bjorn
Lomborg. Data Source: National Oceanic and Atmospheric Administration.

According to a study on the potential of climate-change-related impacts on flooding in the United States and Europe, published in the Journal of Hydrology, “The number of significant [flooding] trends was about the number expected due to chance alone. … The results of this study, for North America and Europe, provide a firmer foundation and support the conclusion of the IPCC that compelling evidence for increased flooding at a global scale is lacking.”2

Further, a 2014 study titled “Flood Risk and Climate Change: Global and Regional Perspectives,”3 published in the Hydrological Sciences Journal,examined claims in the IPCC’s Fifth Assessment Report and concluded that “presently we have only low confidence in numerical projections of changes in flood magnitude or frequency resulting from climate change.”4

References:

  1. Sonia I. Seneviratne and Neville Nicholls, coordinating lead authors, “Changes in
    Climate Extremes and Their Impacts on the Natural Physical Environment,” Chapter 3,
    A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate
    Change, Cambridge University Press, pp. 109–230, https://www.ipcc.ch/site/assets/
    uploads/2018/03/SREX-Chap3_FINAL-1.pdf
  2. Glenn A. Hodgkins et al., “Climate-Driven Variability in the Occurrence of Major Floods
    Across North America and Europe,” Journal of Hydrology, Volume 552, September
    2017, pp. 704–717, http://mural.maynoothuniversity.ie/11682/1/MurphyCo_Climatedriven_
    2017.pdf
  3. Zbigniew W. Kundzewicz et al., “Flood Risk and Climate Change: Global and Regional
    Perspectives,” Hydrological Sciences Journal, Volume 59, Issue 1, 2014, https://www.
    tandfonline.com/doi/full/10.1080/02626667.2013.857411
  4. Dennis L. Hartmann, Albert M.G. Klein Tank, and Matilde Rusticucci, coordinating lead
    authors, “Observations: Atmosphere and Surface: Supplementary Material,” Chapter 2,
    Climate Change 2013: The Physical Science Basis, a contribution of Working Group I to
    the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, 2013,
    pp. 2SM-1–2SM-26, http://www.climatechange2013.org/images/report/WG1AR5_
    Ch02SM_FINAL.pdf

Climate At A Glance is a Project of The Heartland Institute

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