“Typhoon Haiyan; Worse than hell”

Last week a Filipino diplomat gave a passionate speech in Warsaw during the climate change conference. He linked the disaster to man-made climate change and "urged the world to wake up". 

The economist (2013) called it “one of the strongest storms ever recorded” and commented that the Filipino government are insisting that man-made climate change is heightening the risk of typhoon.  Also, David Cameron had acknowledged the fact that climate change may have influenced the ‘increasing’ number of extreme weather (Guardian 2013). I want to explore the above statements and question whether disaster like Haiyan would become more common, and with it social disorder.

Fig 1: Projected surface temperature changes for early and late 21^st century relative to the period 1980-1999 (source; IPCC fourth assessment report: Climate change2007) 

figure 2 source  Race et al (2010) 

Figure 3a and 3b source Webster et al(2005) 

The association between climate change and increase in hurricane activity is complex in nature. It is well known that SST (Sea Surface Temperature) >26 degree is required for the formation of tropic cyclones. The IPCC 2007 report has shown that temperature would increase under all the scenarios and especially that of SST (fig1).  Would that point to higher frequencies of hurricane formations? 

A study conducted by Race et al (2010) has shown that there is a high correlation (up to 0.7 for some points) between SST and storm counts in the month of August off the coast of West Africa. However, this is specific in nature and could not be generalized for all ocean basin. Webster et al(2005) noted that there are possible influence of interannual variability associated with El Nino and the North Atlantic Oscillation which make it hard to draw relation between future increase SST and frequency of hurricane.

Figure 3 showed statistically there is no correlation between increase in the number of Storm days (or number of storm) in relation to the increasing level SST in all ocean Basin. On the other hand, there is substantial decadal-scale oscillation that is especially evident in the number of tropical cyclone days. For example, it peaked at 970 days around 1995 and decreased by 25% to 600 days in 2003.

Figure 3c source Webster et al(2005) 

Figure 4 source Webster et al(2005) 

Figure 3c also showed there is no statistically significant trend linking increasing SST and number of hurricane and displays the same trend as figure 3a/b. The exception is data for the North Atlantic (NATL), which also corresponds to the data found by Race et al (2010), where there is a statistically significant increase in hurricane starting from 1995 in relation to the increased levels of SST.

However, without any comparable correlation in other ocean basin where SST is increasing it means we cannot simply associated the number of storms to a warming SST environment. The ‘coincidence’ in the North Atlantic region, coupled with statistically positive results has fuelled speculation this was the result of climate change via higher SST

More importantly, Webster et al(2005) observed an increase in hurricane intensity between the same periods. As shown in figure 4, strongest categories (4 and 5) have nearly doubled in numbers, occurring in all ocean basins. Emanuel (2005)'s model might provide a insight into the future intensity of hurricanes. His model suggests that an increase of 2 degrees in tropic SST would increase wind speed by 10% and power dissipation by 40-50%. 

Webster et al(2005)'s paper indicates that in the last 30 years, there has been a trend towards more intense hurricanes and they seem to be right. Their observation is consistent with that of Knston et al 2010 (Using a CMIP3 generation model).Their climate model with scenario A1B from IPCC 2007 (for late twenty-first century) predicts there will be an increase in intensity of tropical cyclones of around 2-11% by 2100, and the frequencies of these types of cyclones would increase as well. On the other hand, the general frequency of tropical cyclones would decrease by 6-34%. 

Figure 5 source Emanuel 2013

Figure 6 source  Emanuel 2013

The latest finding from Emanuel (2013) (using a CMIP5-generation global climate model) complicates the picture between climate change, frequency and intensity. One of the main point is that it shows the global frequency of downscaled tropical cyclones will increase throughout the century by around 10-40%, contrary to the results from Knston et al (2010) (not saying they are wrong). The location of the increases in frequencies of tropical cyclones is also shown in fig.5, concentrating in the North Pacific, coincidentally, in the same region as Typhoon Haiyan. At the same time, the increases in the intensity measure by power dissipation index is consistent with the increase in track density (fig 5), concentrating in the North Pacific region. Power dissipation at landfall will increase by around 55% over this century.

The above have shown climate change wasn't the cause of typhoon Haiyan. Evidence suggests climate change up to this point had no/little influence over the frequencies of cyclone formation or to some extent its intensity. Instead, Typhoon Haiyan should be a wakeup call to the vulnerability across the global, especially those near the coastline. The North Pacific region is of concern since the increases in intensity of smaller cyclones are concentrated in that region, whilst frequencies of these small typhoons are also on a upward trend. It also exposes the complex nature of modelling future cyclone behaviour, where results will differ depending on the type of model used, which adds uncertainty to the discourse.

 More importantly, the physicality of the hurricane is only one of the main factors that increases the vulnerability of population. A host of factors from climate change (sea level etc) and human factors (preparedness or GDP ppp etc) also determines the level of social disorder. Hence, I am just showing you one side of the story and the future behaviour of hurricanes should be of concern!