On Holland and Bruyère (2013) “Recent Intense Hurricane Response to Global Climate Change”

Alternate Title: Climate Science Community Continues to Lose Sight of Reality

SkepticalScience is promoting the Holland and Bruyère (2013) paper Recent Intense Hurricane Response to Global Climate Change as proof positive that hypothetical human-induced global warming has caused more intense hurricanes. See Dana Nuccitelli’s post New Research Shows Humans Causing More Intense Hurricanes. My Figure 1 is Figure 1 from Holland and Bruyère (2013).

Figure 1

The abstract of Holland and Bruyère (2013) begins:

An Anthropogenic Climate Change Index (ACCI) is developed and used to investigate the potential global warming contribution to current tropical cyclone activity. The ACCI is defined as the difference between the means of ensembles of climate simulations with and without anthropogenic gases and aerosols. This index indicates that the bulk of the current anthropogenic warming has occurred in the past four decades, which enables improved confidence in assessing hurricane changes as it removes many of the data issues from previous eras.

That’s right; referring to Figure 1, Holland and Bruyère (2013) created an index by subtracting the multi-model mean of climate models forced by natural factors (variations in solar activity and volcanic aerosols) from the mean of the simulations that are also forced with anthropogenic factors like manmade greenhouse gases—as if the two types of model simulations and their difference represent reality. They then used that model-based index, with little to no basis in the real world, for comparisons to hurricane activity at various hurricane strengths.

Hurricane activity is influenced by tropical sea surface temperatures. Yet, we know climate models cannot simulate sea surface temperatures over the past 31 years, which is included in the 1975 to 2010 period studied by Holland and Bruyère (2013). Refer to the post here for a model-data comparison of satellite-era sea surface temperature anomalies. And we’ve also discussed for 4 years how ocean heat content data and satellite-era sea surface temperature data indicate the oceans warmed naturally. Refer to the illustrated essay “The Manmade Global Warming Challenge” [42MB]. The models are obviously flawed.

Hurricane activity is also influenced by the El Niño-Southern Oscillation (ENSO). There are fewer Atlantic hurricanes during El Niño years due to the increase in wind shear there. On the other hand, there’s an increase in the intensity of eastern tropical Pacific cyclones during El Niño years. See Table 1, which is from the NOAA Weather Impacts of ENSO webpage.

Table 1

Does Holland and Bruyère (2013) consider ENSO? No. The words El Niño and La Niña do not appear in the paper, and ENSO appears only once, when they’re discussing the reason for the use of 5-year smoothing.

All variance numbers use the 5-years smoothed annual time series to remove ENSO type variability.

Can climate models simulate ENSO? The answer is also no. Refer to the post Guilyardi et al (2009) “Understanding El Niño in Ocean-Atmosphere General Circulation Models: progress and challenges”.

Guilyardi et al (2009) includes:

Because ENSO is the dominant mode of climate variability at interannual time scales, the lack of consistency in the model predictions of the response of ENSO to global warming currently limits our confidence in using these predictions to address adaptive societal concerns, such as regional impacts or extremes (Joseph and Nigam 2006; Power et al. 2006).

The multidecadal variability of the sea surface temperatures in the North Atlantic is called the Atlantic Multidecadal Oscillation or AMO. There are numerous papers that discuss the influence of the Atlantic Multidecadal Oscillation on hurricane activity. In fact, the NOAA Frequently Asked Questions About the Atlantic Multidecadal Oscillation (AMO) includes the question Does the AMO influence the intensity or the frequency of hurricanes (which)? Their answer reads:

The frequency of weak-category storms – tropical storms and weak hurricanes – is not much affected by the AMO. However, the number of weak storms that mature into major hurricanes is noticeably increased. Thus, the intensity is affected, but, clearly, the frequency of major hurricanes is also affected. In that sense, it is difficult to discriminate between frequency and intensity and the distinction becomes somewhat meaningless.

The AMO began its multidecadal rise in temperature in the mid-1970s. See Figure 2. By focusing their analysis on the period of 1975 to 2010, Holland and Bruyère (2013) appear to be, in part, attempting to blame manmade greenhouse gases for an increase in activity that’s already been attributed to the natural variability of the AMO.

Figure 2

Off topic note: Referring to Figure 1 from Holland and Bruyère (2013), notice how the surface temperature data ends in 1999 in cell b, while the models continue for a number of years beyond then, probably to the 2005 end year of the historic CMIP5 simulations. Apparently, some climate scientists haven’t figured out what assumption a reader is forced to make when he or she sees disparities in the end dates of model-data comparisons—that the models would show very poorly if Holland and Bruyère (2013) had extended the data to the end year of the historic simulations, 2005, or to the end year of their study, which was 2010. Note also that the data begins after the start year of the models, too. In other words, most readers wonder what the authors are hiding and assume the worst.

CLOSING

Holland and Bruyère (2013) appears to be a flawed attempt to counter the findings of the recent (2012) IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX). See the Summary for Policymakers here. The IPCC writes:

There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities.

Holland and Bruyère (2013) is yet another peer-reviewed study that relies on climate models as if the models represent reality, when climate models clearly do not. Eventually, the climate science community will have to come to terms with this—possibly not in my lifetime at the rate they’re going. And the portrayers of gloom and doom at SkepticalScience like Dana Nuccitelli somehow find papers like Holland and Bruyère (2013) to be credible. Nothing surprising about that.