We welcome the comments of Landsea (2015, hereafter L15) and we1 applaud his efforts toward reanalyzing past tropical cyclone data in the Atlantic (Landsea et al. 2008, 2012, 2014; Hagen et al. 2012). However, L15 does not substantially change the conclusions stated in Kunkel et al. (2013, hereafter K13). L15 voices two main concerns:
The U.S. landfalling hurricane time series considered by K13 is dated.
The U.S. landfall record exhibits multidecadal variability that places the changes since 1970 into a larger perspective than K13 provided. Related to this concern, L15 introduces assertions about the relationship between U.S. landfall variability and basinwide North Atlantic variability.
We will address each of these points here:
K13 stated “Landfalling tropical cyclone activity in the United States, as well as East Asia, shows no significant long-term trends (e.g., Landsea 2005)” (p. 506). We are not aware of any published papers that have updated the U.S. landfalling hurricane time series beyond the papers cited in K13 [including not just Landsea (2005) but also Vecchi and Knutson (2011)]. L15’s inference that K13 presented dated information is not supported and the update introduced by L15 is in complete agreement with the statements of K13.
K13 stated “Owing to pronounced multidecadal variability evident in longer-term records of Atlantic basinwide or U.S. landfalling tropical cyclone frequency (e.g., Vecchi and Knutson 2011, see their Fig. 5), the period since around 1970 (e.g., Fig. 5) appears to be too short to draw confident inferences about longer-term (e.g., century scale) trends in Atlantic tropical cyclone activity” (p. 506). L15 fundamentally concurs with the broader perspective that K13 provides about the inability to draw confident inferences about century-scale trends from the observed post-1970 Atlantic activity.
In K13, a conscious choice was made to focus on the increases over the shorter period since the 1970s and address the attribution for these increases, because much of the state of knowledge is being actively promulgated on this shorter period. This is demonstrated by the citations in K13 as well as the IPCC Fifth Assessment Report (Bindoff et al. 2014) published subsequent to K13. The contrasting emphases of K13 and L15 are both important; one does not preclude the other, and the emphasis of L15 has been previously addressed (e.g., Knutson et al. 2010; Seneviratne et al. 2012; Hartmann et al. 2014; Zwiers et al. 2013). Anthropogenically forced change and internal climate variability have most likely affected North Atlantic hurricane activity and sea surface temperatures in a broad range of ways, and the quantification of these influences remains a significant research challenge (Dunstone et al. 2013; Tung and Zhao 2013; Zhang et al. 2013; Carslaw et al. 2013; Mann et al. 2014). Century-scale trends forced by steadily increasing greenhouse gases are not the only focus of detection and attribution studies and should not define the state of knowledge.
Statements about the relationship between U.S. landfall variability and basinwide variability remain controversial (Holland 2007), and we would argue that the statements of L15 should be subjected to a more formal review than a comment/reply exchange provides. In addition to the decreased signal-to-noise ratio of measured trends when subsetting basinwide activity (K. Nzerem et al. 2006, unpublished manuscript; Emanuel 2011), there are substantial questions about whether U.S. landfalling activity can serve as an adequate proxy for basinwide North Atlantic activity when there are systematic and significant relationships between climate and tropical cyclone track variability (Kossin et al. 2010, 2014). This latter point was discussed briefly in K13. Finally, although the correlation of 0.49 identified by L15 is statistically significant, the associated common variance of only 24% emphasizes that the variability of the U.S. landfall record leaves a very large part (76%) of the basinwide variance unexplained.
Given the importance of understanding changes in the U.S. landfalling hurricane activity and how they relate to basinwide North Atlantic variability and trends, we feel that it is crucial to have the data and methods, as well as assertions of common variance between landfall and basinwide activity, subjected to a more formal and complete peer review, and we hope that Landsea and/or others will undertake a more thorough study.
REFERENCES
Bindoff, N. L., and Coauthors, 2014: Detection and attribution of climate change: from global to regional. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 867–952.
Carslaw, K. S., and Coauthors, 2013: Large contribution of natural aerosols to uncertainty in indirect forcing. Nature, 503, 67–71, doi:10.1038/nature12674.
Dunstone, N. J., D. M. Smith, B. B. B. Booth, L. Hermanson and R. Eade, 2013: Anthropogenic aerosol forcing of Atlantic tropical storms. Nat. Geosci., 6, 534–539, doi:10.1038/NGEO1854.
Emanuel, K., 2011: Global warming effects on U.S. hurricane damage. Wea. Climate Soc., 3, 261–268, doi:10.1175/WCAS-D-11-00007.1.
Hagen, A. B., D. Strahan-Sakoskie, and C. Luckett, 2012: A reanalysis of the 1944–53 Atlantic hurricane seasons—The first decade of aircraft reconnaissance. J. Climate, 25, 4441–4460, doi:10.1175/JCLI-D-11-00419.1.
Hartmann, D. L., and Coauthors, 2014: Observations: Atmosphere and surface. Climate Change 2013: The Physical Science Basis, T. F. Stocker et al., Eds., Cambridge University Press, 159–254.
Holland, G. J., 2007: Misuse of landfall as a proxy for Atlantic tropical cyclone activity. Eos, Trans. Amer. Geophys. Union, 88, 349–356, doi:10.1029/2007EO360001.
Knutson, T. R., and Coauthors, 2010: Tropical cyclones and climate change. Nat. Geosci., 3, 157–163, doi:10.1038/ngeo779.
Kossin, J. P., S. J. Camargo, and M. Sitkowski, 2010: Climate modulation of North Atlantic hurricane tracks. J. Climate, 23, 3057–3076, doi:10.1175/2010JCLI3497.1.
Kossin, J. P., K. A. Emanuel, and G. A. Vecchi, 2014: The poleward migration of the location of tropical cyclone maximum intensity. Nature, 509, 349–352, doi:10.1038/nature13278.
Kunkel, K. E., and Coauthors, 2013: Monitoring and understanding trends in extreme storms: State of knowledge. Bull. Amer. Meteor. Soc., 94, 499–514, doi:10.1175/BAMS-D-11-00262.1.
Landsea, C. W., 2005: Hurricanes and global warming. Nature, 438, E11–E12, doi:10.1038/nature04477.
Landsea, C. W., 2015: Comments on “Monitoring and understanding trends in extreme storms: State of knowledge.” Bull. Amer. Meteor. Soc., 96, 1175–1176, doi:10.1175/JCLI-D-13-00211.1.
Landsea, C. W., and Coauthors, 2008: A reanalysis of the 1911–20 Atlantic hurricane database. J. Climate, 21, 2138–2168, doi:10.1175/2007JCLI1119.1.
Landsea, C. W., S. Feuer, A. Hagen, D. A. Glenn, J. Sims, R. Perez, M. Chenoweth, and N. Anderson, 2012: A reanalysis of the 1921–30 Atlantic hurricane database. J. Climate, 25, 865–885, doi:10.1175/JCLI-D-11-00026.1.
Landsea, C. W., A. Hagen, W. Bredemeyer, C. Carrasco, D. A. Glenn, A. Santiago, D. Strahan-Sakoskie, and M. Dickinson, 2014: A reanalysis of the 1931 to 1943 Atlantic hurricane database. J. Climate, 27, 6093–6118, doi:10.1175/JCLI-D-13-00503.1.
Mann, M. E., B. A. Steinman, and S. K. Miller, 2014: On forced temperature changes, internal variability, and the AMO. Geophys. Res. Lett., 41, 3211–3219, doi:10.1002/2014GL059233.
Seneviratne, S. I., and Coauthors, 2012: Changes in climate extremes and their impacts on the natural physical environment. Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, C. B. Field et al., Eds., Cambridge University Press, 109–230.
Tung, K.-K., and J. Zhou, 2013: Using data to attribute episodes of warming and cooling in instrumental records. Proc. Natl. Acad. Sci. USA, 110, 2058–2063, doi:10.1073/pnas.1212471110.
Vecchi, G. A., and T. R. Knutson, 2011: Estimating annual numbers of Atlantic hurricanes missing from the HURDAT database (1878–1965) using ship track density. J. Climate, 24, 1736–1746, doi:10.1175/2010JCLI3810.1.
Zhang, R., and Coauthors, 2013: Have aerosols caused the observed Atlantic multidecadal variability? J. Atmos. Sci., 70, 1135–1144, doi:10.1175/JAS-D-12-0331.1.
Zwiers, F. W., and Coauthors, 2013: Challenges in estimating and understanding recent changes in the frequency and intensity of extreme climate and weather events. Climate Science for Serving Society: Research, Modeling and Prediction Priorities. G. R. Asrar and J. W. Hurrell, Eds., Springer, 339–389.
