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Posted on: September 20, 2020

Hurricane Katrina | Damage, Deaths, Aftermath, & Facts | Britannica
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Thomas Knutson


CITATION: An increase in global trends of tropical cyclone translation speed since 1982 and its physical causes. Sung-Hun Kim1,2, Il-Ju Moon1 and Pao-Shin Chu2. Published 2 September 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd. Environmental Research Letters, Volume 15, Number 9

ABSTRACT: In this study, the causes of the increase in global mean tropical cyclone translation speed (TCTS) in the post-satellite era were investigated. Analysis reveals that the global-mean TCTS increased by 0.31 km h−1 per decade over the last 36 years, but the steering flow controlling the local TCTS decreased by −0.24 km h−1 per decade in the major tropical cyclone (TC) passage regions. These values correspond to a change of 5.9% and −5.6% during the analysis period for the mean TCTS and steering flow, respectively. The inconsistency between these two related variables (TCTS and steering flows) is caused by relative TC frequency changes according to basin and latitude. The TCTS is closely related to the latitude of the TC position, which shows a significant difference in mean TCTS between basins. That is, the increased global-mean TCTS is mainly attributed to the following: (1) an increase (4.5% per decade) in the relative proportion of the North Atlantic TCs in terms of global TC’s position points (this region has the fastest mean TCTS among all basins); and (2) the poleward shift of TC activities. These two effects account for 76.8% and 25.8% of the observed global-mean TCTS trend, respectively, and thus overwhelm those of the slowing steering flow related to the weakening of large-scale tropical circulation, which leads to a global mean increase in TCTS. Given that TC activity in the North Atlantic is closely related to the Atlantic Multi-decadal Oscillation and a poleward shift of TC exposure is likely induced by global warming, the recent increase in the global-mean TCTS is a joint outcome of both natural variations and anthrophonic effects. FULL TEXT PDF:


  1. The expected impacts of anthropogenic global warming on tropical cyclones were derived from AGW theory using a large array of climate model runs by Thomas Knutson and more than a dozen co-authors that included Kerry Emanuel, Chris Landsea, James Kossin, Gabriel Vecchi, Phillip Klotzbach, and other notable researchers in this field. See for example: Knutson, Thomas R., John L. McBride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava, and Masato Sugi. “Tropical cyclones and climate change.” Nature geoscience 3, no. 3 (2010): 157-163. … Also Walsh, Kevin JE, John L. McBride, Philip J. Klotzbach, Sethurathinam Balachandran, Suzana J. Camargo, Greg Holland, Thomas R. Knutson et al. “Tropical cyclones and climate change.” Wiley Interdisciplinary Reviews: Climate Change 7, no. 1 (2016): 65-89.
  2. What we find in these studies is the theoretical basis for the impact of AGW on tropical cyclones that serves as the starting point for empirical research in this field in the form of formulating the hypothesis to be tested against observations. In summary, this theoretical basis derived from the cited works above is as follows: “Tropical cyclones and climate change.” Nature geoscience 3.3 (2010): 157-163. In the paper, Tom Knutson spells out exactly what climate science claims in terms of the impact of AGW climate change on tropical cyclones with climate model predictions of the effect of rising SST on tropical cyclones. His main points are as follows: (1) Globally averaged intensity of tropical cyclones will rise as AGW increases SST. Models predict globally averaged intensity increase of 2% to 11% by 2100. (2). Models predict falling globally averaged frequency of tropical cyclones with frequency decreasing 6%-34% by 2100. (3). The globally averaged frequency of “most intense tropical cyclones” should increase as a result of AGW. The intensity of tropical cyclones is measured as the ACE (Accumulated Cyclone Energy). (4). Models predict increase in precipitation within a 100 km radius of the storm center. A precipitation rise of 20% is projected for the year 2100. (5) Extremely high variance in tropical cyclone data at an annual time scale suggests longer, perhaps a decadal time scale which in turn greatly reduces statistical power. (6) Model projections for individual cyclone basins show large differences and conflicting results. Thus, no testable implication can be derived for studies of individual basins.
  3. As shown in related posts, tests for these hypotheses have mostly failed: LINK#1: LINK#2: LINK#3: LINK#4: LINK#5:
  4. An apparent success in this line of research that is still cited is the Hurricane Katrina paper by Kerry Emanuel on the destructiveness of hurricanes. The paper found that AGW was making Hurricanes of the North Atlantic Basin more destructive. However, as shown in a related post on this site, this paper suffers from fatal statistical errors and the findings are therefore discarded on this basis. Emanuel also violated the Knutson etal principle against restricting the study to selected cyclone basins. LINK TO THE EMANUEL PAPER
  5. We also find in the Emanuel paper, and in many similar papers, a violation of the Knutson 2010 principle that tropical cyclone studies in the context of climate change must include all five basins in the for of a bias for the North Atlantic Basin to the exclusion of the other five tropical cyclone basins LINK
  6. Within the strict guidelines of the Knutson paper and the principles of empirical research and of statistics, the effort by climate science to relate the destruction of tropical cyclones to climate change has failed. Yet there remains a yearning in climate science for such a relationship. A possible reason for that yearning is that the dramatic destruction of tropical cyclones, as for example by Hurricane Katrina, provides a convincing argument for climate action and against fossil fuels.
  7. This line of research therefore persists but the hypotheses to be tested no longer bears a relationship to the original theoretical basis by way of SST whereby AGW increases SST and higher SST increases cyclone energy. Such new tropical cyclone hypotheses, as the one under review here, are apparently derived from whatever pattern can be found in the data.
  8. As an example, we describe in a related post LINK , a study that found that climate change is changing the global pattern of tropical cyclones with the finding that since 1980, cyclone activity has tempered and decreased in the South Indian and West Pacific basins and increased in the East Pacific and North Atlantic basins. This pattern was then stated as the hypothesis to be tested in a new empirical work on tropical cyclones in which they found that climate change had caused a shift in the global pattern of tropical cyclone activity with a weakening in the South Indian and West Pacific basins and a strengthening in the North Atlantic and East Pacific basins {Detected climatic change in global distribution of tropical cyclones, Hiroyuki Murakami etal, Proceedings of the National Academy of Sciences May 2020, 201922500; DOI: 10.1073/pnas.1922500117}
  9. There are three issues with this study that nullifies the findings. First, it is not possible to test a hypothesis with the data used to construct the hypothesis. That is a severe form of circular reasoning called the Texas Sharpshooter Fallacy. The second issue is that causation is assumed simply from a co-occurrence. Co-occurrence does not prove causation. The third issue in this research is that it is entirely unrelated to the only theoretical format for the study of tropical cyclones in the context of climate change as laid out in Knutson et al 2010. The findings are rejected on this basis.
  10. The paper under review in this post, {An increase in global trends of tropical cyclone translation speed since 1982 and its physical causes. Sung-Hun Kim1,2, Il-Ju Moon1 and Pao-Shin Chu2, 2020} is rejected on the same basis. The hypothesis to be tested is not derived from theory but from the data and then the same data are used to test the hypothesis. Also, the hypothesis is unrelated to Knutson etal 2010 and no source is cited for the theoretical basis of this hypothesis.
  11. The essential finding in these kinds of studies is that the authors found a pattern in the data with the implication that this pattern is relevant in the study of climate change impacts on tropical cyclones and that it should therefore be considered a climate change impact. The research methodology violates research norms and the findings are rejected on that basis.
  12. More on such AGW impact research: LINK

Thomas Knutson

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