Thongchai Thailand

TROPICAL CYCLONES CLIMATE CHANGE

Posted on: May 6, 2020

THE WEST PACIFIC BASINNWP-GIF

THE NORTH ATLANTIC BASINNA-GIF

THE EAST PACIFIC BASINNEP-GIF

THE NORTH INDIAN BASINNIO-GIF

 

[LINK TO THE HOME PAGE OF THIS SITE]

RELATED POSTS ON TROPICAL CYCLONES: [LINK] [LINK] [LINK] [LINK] [LINK] [LINK] [LINK] [LINK] 

 

 

THIS POST IS A CRITICAL REVIEW OF A RESEARCH PAPER [LINK] WITH THE FINDING THAT THE IMPACT OF AGW CLIMATE CHANGE ON TROPICAL CYCLONES IS “THE SPATIAL PATTERN OF THEIR OCCURRENCE RATHER THAN THE NUMBER OF TROPICAL CYCLONES GLOBALLY”. THE STUDY PERIOD IS 1980-2018. THE PAPER WAS REVIEWED BY KERRY EMANUEL WHOSE WORK ON TROPICAL CYCLONES IS DISCUSSED IN A RELATED POST [LINK] 

Kerry Emanuel and his Hurricane Destructiveness Chart

 

PART-1: CITATION AND ABSTRACT

Detected climatic change in global distribution of tropical cyclones, 
Hiroyuki Murakami etal, 
ABSTRACT: Owing to the limited length of observed tropical cyclone data and the effects of multidecadal internal variability, it has been a challenge to detect trends in tropical cyclone activity on a global scale. However, there is a distinct spatial pattern of the trends in tropical cyclone frequency of occurrence on a global scale since 1980, with substantial decreases in the southern Indian Ocean and western North Pacific and increases in the North Atlantic and central Pacific. Here, using a suite of high-resolution dynamical model experiments, we show that the observed spatial pattern of trends is very unlikely to be explained entirely by underlying multidecadal internal variability; rather, external forcing such as greenhouse gases, aerosols, and volcanic eruptions likely played an important role. This study demonstrates that a climatic change in terms of the global spatial distribution of tropical cyclones has already emerged in observations and may in part be attributable to the increase in greenhouse gas emissions.
THE “SIGNIFICANCE” OF THIS WORK IS DESCRIBED AS: Little had been known about whether the ongoing climate changes had already affected observed global tropical cyclones (TCs). This study revealed that a climate change in global TC activity over 1980 to 2018 has been more evident in the spatial pattern of TC occurrence, rather than the number of global TCs. The total effect of anthropogenic greenhouse gases, aerosols, and volcanic eruptions on global TC distribution is spatially inhomogeneous: Increases and decreases in TC occurrence depend on the region. However, our climate models project decreases in the number of global TCs toward the end of the 21st century due to the dominant effect of greenhouse gases on decreasing TC occurrence in most of the tropics, consistent with many previous studies.

 

PART-2: WHAT THE PAPER SAYS

The paper says that when the authors looked at the global tropical cyclone data 1980-2018 they did not find evidence for the the prior climate science hypothesis that AGW will increase the number of tropical cyclones worldwide particularly so in terms of the large variance and uncertainty in the data. When they looked at the data cyclone basin by cyclone basin they found that the reason for the absence of a trend in the global frequency of tropical cyclones is that the frequency has increased in some basins while they decreased in other basins. A further study of tropical cyclone frequency basin by basin revealed a trend in the pattern of the spatial distribution of the frequency of tropical cyclones. In their own words, “However, when we look at a global map of the trend in TC frequency of occurrence since 1980 , there is a pronounced spatial pattern in the trends, namely, decreasing trends in the southern Indian Ocean, western North Pacific, Coral Sea off the northeast coast of Australia, and the far eastern tropical North Pacific, but increasing trends in the Arabian Sea, central Pacific including Hawaii, and the North Atlantic.

It was then that they decided to test the hypothesis that impact of AGW climate change is not on the global frequency of tropical cyclones but on their distribution among the cyclone basins. In their words, “We wish to assess whether anthropogenic climate change could play a role in driving this spatial pattern in the global trends of TCF”  The paper is a test of this hypothesis with the data and findings summarized in the chart below.  The finding is that 

F1.large (1)

Having identified the changing pattern of tropical cyclone distribution without a change in global frequency in the period 1980-2018, the authors then used climate models to determine whether the observed changes in the global distribution of an unchanging number of tropical cyclones could be explained in terms of climate forcings. The climate models showed that with the right portfolio of forcings including terrestrial volcanism, they could explain the changing pattern in an unchanging global frequency of tropical cyclones in the study period 1980-2018 (chart below).

F4.large

 

 

PART-3: CRITICAL COMMENTARY  

  1. THIS STUDY WOULD HAVE BEEN MORE CREDIBLE IF THE HYPOTHESIS TO BE TESTED WERE DERIVED FROM THEORY OR FROM THE MODELS AS KNUTSON (2010) HAD DONE WHERE TOM KNUTSON AND HIS MANY CO-AUTHORS INCLUDING KERRY EMANUEL USED A LARGE NUMBER OF CLIMATE MODEL RUNS TO DETERMINE THE THEORETICAL IMPACT OF AGW CLIMATE CHANGE ON TROPICAL CYCLONES LISTED BELOW. THE AUTHORS OF THIS PAPER DID NOT DO THAT.
  2. INSTEAD WHAT WE FIND HERE IS THAT THE HYPOTHESIS WAS DERIVED FROM THE DATA AND THEN VERIFIED WITH CLIMATE MODELS LEAVING OPEN THE POSSIBILITY THAT THE FORCINGS AND OTHER MODEL PARAMETERS USED TO VERIFY THE THEORETICAL VALIDITY OF THE HYPOTHESIS WERE FINE TUNED TO CREATE THE DESIRED RESULT .
  3. HOWEVER, IN FIELDS SUCH AS CLIMATE SCIENCE, ECONOMICS, FINANCE, POPULATION STUDIES, AND SO ON, THERE ARE MANY RESEARCHERS AND MANY HYPOTHESES BUT ONLY ONE HISTORY AND ONLY ONE DATA TIME SERIES RELEVANT TO THE RESEARCH QUESTION. IT IS NOT POSSIBLE IN THIS CONTEXT TO TEST A HYPOTHESIS THAT IS DERIVED FROM THE DATA BECAUSE THERE IS NO INDEPENDENT DATA WITH WHICH TO TEST THE HYPOTHESIS. THE TEST OF A HYPOTHESIS WITH THE SAME DATA USED TO CONSTRUCT THE HYPOTHESIS IS CIRCULAR REASONING.
  4. THE USE OF CLIMATE MODELS AFTER THE FACT DOES NOT VALIDATE THE FINDING BECAUSE IT OPENS THE POSSIBILITY OF FINE TUNING THE FORCINGS AND OTHER MODEL PARAMETERS TO VERIFY THE FINDING THAT HAS ALREADY BEEN DETERMINED FROM THE DATA.
  5. THEREFORE THE FINDING IN THIS PAPER THAT CLIMATE CHANGE HAS CAUSED THE CHANGE IN TROPICAL CYCLONE DISTRIBUTION THAT WAS FOUND IN THE DATA IS FLAWED BECAUSE IT CAN BE EXPLAINED IN TERMS OF CIRCULAR REASONING AND CONFIRMATION BIAS

 

Knutson, Thomas R., et al. “Tropical cyclones and climate change.” Nature geoscience 3.3 (2010): 157-163.   (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) Model projections for individual cyclone basins show large differences and conflicting results. Thus, no testable implication can be derived for studies of individual basins.   

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