8.2.2 Climate Change Implications
and Projected Changes
One of the serious concerns of climate change is the impacts
of SST warming on frequency, intensity, and duration of
TCs which remain elusive particularly for the tropical oceans
(e.g., IPCC 2007, 2014; Elsner and Kocher 2000; Pielke
2005; Emanuel 2005; Anthes et al. 2006; Elsner et al. 2008;
Xie et al. 2010; Knutson et al. 1998, 2010a, b; Ramesh
Kumar and Sankar 2010). The NIO region witnessed a rapid
rise in SSTs from 1950s by about 0.6 °C as compared to
other tropical ocean basins (see Mohanty et al. 2012). Some
of the earlier studies implied that changing SST trends and
rising intense TCs in the NIO region may have consequences
from anthropogenic climate change (e.g., Knutson et al.
2006; Elsner et al. 2008; Knutson et al. 2019b). Knutson
et al. (2010b) also suggested that climate change signal to
changes in SST and associated TC activity might emerge
sooner in the Indian Ocean as compared to other ocean
basins. Another potential concern in the NIO region is that
TC intensities particularly in the AS region exhibit an
unprecedented rise in the recent years (see Table 8.2).
High-resolution global climate model experiments indicate
that anthropogenic global warming has increased the probability of extremely severe cyclonic systems during the
post-monsoon season in the AS region (Murakami et al.
2017). Although the investigations concerned with TC
changes in the AS region are limited at this time, some
recent studies suggest that increasing anthropogenic emissions of black carbon and sulfate can play a role in reducing
the vertical wind shear so as to favor more intense TC
activity in the AS region (Evan et al. 2011, 2012; Wang et al.
2012).
Many climate modeling investigations generally suggest
that increasing or doubling of carbon dioxide (CO 2 ) may
enhance the frequency of severe/most intense cyclonic
storms (e.g., Knutson et al. 2001; Knutson and Tuleya 2004;
Webster et al. 2005; Oouchi et al. 2006; Bengtsson et al.
2007; Klotzbach and Landsea 2015). Some past studies such
as Danard and Murthy (1989) and Yu and Wang (2009)
pointed out that there could be an increase in TC frequency
and TC intensity over the NIO basin in a doubled CO 2
world. Here, it is noteworthy to mention that there is a
reasonable degree of sophistication in the current generation
climate models that are capable of reproducing not only the
salient features of TCs but also the associated dynamical–
physical processes behind their development (e.g., Vidale
et al. 2010). One can readily expect that warmer and wetter
climate may favor more TCs with higher intensities from the
climate change experiments using climate models. Despite
that there is a consistency with the observed globally
declining frequency of TCs in response to global warming
from these experiments (Sugi et al. 2002; McDonald et al.
2005; Yoshimura et al. 2006; Knutson et al. 2010a, 2019b),
the inferences were rather dubious for basin-wide TC
changes and more for the NIO region in particular (see also
Zhao and Held 2012). Long-period trend assessment
(International Panel on Climate Change Fifth Assessment
Report—IPCC AR5; IPCC 2014) in surface air temperatures
from climate model simulations, participated in CMIP5, for
the historical periods indicates that there is a detectable
warming signal over the Indian Ocean from the beginning of
twentieth century. But, the present-day climate model
assessments for the NIO region apparently present larger
ambiguity due to larger bias in the simulations concerned
with NIO TC activity—while there is a realistic agreement
for TC frequency and intensity changes against observations
for the Atlantic and Pacific Ocean basins (Zhao et al. 2009;
Bender et al. 2010; Knutson et al. 2014). Further, the
reduction in TC frequency over most part of the Indian
Ocean appears to come from equal contributions of rising
CO 2 emissions and anomalous SST patterns—notably, the
SST effect and reduction in vertical shear have more
precedence to the rising numbers of TCs in the AS region
(Sugi et al. 2014).
Through the use of reanalyzed archives, Ramesh Kumar
and Sankar (2010) indicate that the declining frequency of
TCs in the NIO region in the historical period has no clear
bearing global warming signal in association with the rising
SSTs, but the warming signal may have greater impact on
observed changes in atmospheric parameters such as
decreasing mid-tropospheric relative humidity, low-level
vorticity, and vertical wind shear during cyclone seasons of
the NIO region (see also Pattanaik 2005; Sebastian and
Behera 2015). In corroboration with these investigations,
Balaguru et al. (2014) further indicate that intensity of major
TCs in the BOB region during the post-monsoon season
tends to have a coupled response from increasing
upper-ocean content consistent with the rising SSTs and
enhanced convective instability in the atmosphere. Murakami et al. (2017) performed a suite of high-resolution
coupled model experiments and also showed that increasing
anthropogenic-induced warming has potentially increased
the probability of extreme category storms in the AS region,
while the role of natural variability is rather minimal for the
unprecedented rise in TC activity in the AS region.
As compared to other ocean basins, future changes in TC
activity in the NIO region have received less attention in
particular. As for the projected changes in TC activity in
NIO region based on the investigations from climate change
experiments, there is a large inconsistency noted in the
projections from various state-of-the-art climate models.
Knutson et al. (2010a, b) documented that in comparison
with present-day changes, there is a large variation between
8 Extreme Storms
163
and Projected Changes
One of the serious concerns of climate change is the impacts
of SST warming on frequency, intensity, and duration of
TCs which remain elusive particularly for the tropical oceans
(e.g., IPCC 2007, 2014; Elsner and Kocher 2000; Pielke
2005; Emanuel 2005; Anthes et al. 2006; Elsner et al. 2008;
Xie et al. 2010; Knutson et al. 1998, 2010a, b; Ramesh
Kumar and Sankar 2010). The NIO region witnessed a rapid
rise in SSTs from 1950s by about 0.6 °C as compared to
other tropical ocean basins (see Mohanty et al. 2012). Some
of the earlier studies implied that changing SST trends and
rising intense TCs in the NIO region may have consequences
from anthropogenic climate change (e.g., Knutson et al.
2006; Elsner et al. 2008; Knutson et al. 2019b). Knutson
et al. (2010b) also suggested that climate change signal to
changes in SST and associated TC activity might emerge
sooner in the Indian Ocean as compared to other ocean
basins. Another potential concern in the NIO region is that
TC intensities particularly in the AS region exhibit an
unprecedented rise in the recent years (see Table 8.2).
High-resolution global climate model experiments indicate
that anthropogenic global warming has increased the probability of extremely severe cyclonic systems during the
post-monsoon season in the AS region (Murakami et al.
2017). Although the investigations concerned with TC
changes in the AS region are limited at this time, some
recent studies suggest that increasing anthropogenic emissions of black carbon and sulfate can play a role in reducing
the vertical wind shear so as to favor more intense TC
activity in the AS region (Evan et al. 2011, 2012; Wang et al.
2012).
Many climate modeling investigations generally suggest
that increasing or doubling of carbon dioxide (CO 2 ) may
enhance the frequency of severe/most intense cyclonic
storms (e.g., Knutson et al. 2001; Knutson and Tuleya 2004;
Webster et al. 2005; Oouchi et al. 2006; Bengtsson et al.
2007; Klotzbach and Landsea 2015). Some past studies such
as Danard and Murthy (1989) and Yu and Wang (2009)
pointed out that there could be an increase in TC frequency
and TC intensity over the NIO basin in a doubled CO 2
world. Here, it is noteworthy to mention that there is a
reasonable degree of sophistication in the current generation
climate models that are capable of reproducing not only the
salient features of TCs but also the associated dynamical–
physical processes behind their development (e.g., Vidale
et al. 2010). One can readily expect that warmer and wetter
climate may favor more TCs with higher intensities from the
climate change experiments using climate models. Despite
that there is a consistency with the observed globally
declining frequency of TCs in response to global warming
from these experiments (Sugi et al. 2002; McDonald et al.
2005; Yoshimura et al. 2006; Knutson et al. 2010a, 2019b),
the inferences were rather dubious for basin-wide TC
changes and more for the NIO region in particular (see also
Zhao and Held 2012). Long-period trend assessment
(International Panel on Climate Change Fifth Assessment
Report—IPCC AR5; IPCC 2014) in surface air temperatures
from climate model simulations, participated in CMIP5, for
the historical periods indicates that there is a detectable
warming signal over the Indian Ocean from the beginning of
twentieth century. But, the present-day climate model
assessments for the NIO region apparently present larger
ambiguity due to larger bias in the simulations concerned
with NIO TC activity—while there is a realistic agreement
for TC frequency and intensity changes against observations
for the Atlantic and Pacific Ocean basins (Zhao et al. 2009;
Bender et al. 2010; Knutson et al. 2014). Further, the
reduction in TC frequency over most part of the Indian
Ocean appears to come from equal contributions of rising
CO 2 emissions and anomalous SST patterns—notably, the
SST effect and reduction in vertical shear have more
precedence to the rising numbers of TCs in the AS region
(Sugi et al. 2014).
Through the use of reanalyzed archives, Ramesh Kumar
and Sankar (2010) indicate that the declining frequency of
TCs in the NIO region in the historical period has no clear
bearing global warming signal in association with the rising
SSTs, but the warming signal may have greater impact on
observed changes in atmospheric parameters such as
decreasing mid-tropospheric relative humidity, low-level
vorticity, and vertical wind shear during cyclone seasons of
the NIO region (see also Pattanaik 2005; Sebastian and
Behera 2015). In corroboration with these investigations,
Balaguru et al. (2014) further indicate that intensity of major
TCs in the BOB region during the post-monsoon season
tends to have a coupled response from increasing
upper-ocean content consistent with the rising SSTs and
enhanced convective instability in the atmosphere. Murakami et al. (2017) performed a suite of high-resolution
coupled model experiments and also showed that increasing
anthropogenic-induced warming has potentially increased
the probability of extreme category storms in the AS region,
while the role of natural variability is rather minimal for the
unprecedented rise in TC activity in the AS region.
As compared to other ocean basins, future changes in TC
activity in the NIO region have received less attention in
particular. As for the projected changes in TC activity in
NIO region based on the investigations from climate change
experiments, there is a large inconsistency noted in the
projections from various state-of-the-art climate models.
Knutson et al. (2010a, b) documented that in comparison
with present-day changes, there is a large variation between
8 Extreme Storms
163