(medium confidence) over the decade ending in 2012,
reversing the drying trend that occurred from the mid-1970s
to mid-1990s. Human influence has also contributed to
large-scale changes in precipitation patterns over land
(medium confidence; Bindoff et al. 2013). It is likely that,
since about 1950, the number of heavy precipitation events
over land has increased in more regions than it has decreased.
Local changes in temperature affect the cryosphere. The
amount of ice contained in glaciers globally has been
declining every year for over 20 years. Total ice loss from
the Greenland and Antarctic ice sheets during 1992–2011
(inclusive) has been 4260 [3060–5460] Gt, equivalent to
11.7 [8.4–15.1] mm of sea level. However, the rate of
change has increased with time and most of this ice has been
lost in the second decade of the 20-year period (Vaughan
et al. 2013).
The global average sea level rose by 19 cm from 1901 to
2010 (Stocker et al. 2013). The average rate of rise measured
by satellites has been 3.2 [2.9–3.5] mm/year since the 1990s
up from 1.7 [1.5–1.9] mm/year during the twentieth century,
obtained from historical tide gauge records (Hartmann et al.
2013). Thermal expansion and glacier melt because of
anthropogenic global warming have been the major drivers
of rise in global sea levels over the past century.
Substantial losses in Arctic sea ice have been observed
since satellite records began, particularly at the time of the
minimum extent, which occurs in September, at the end of
the annual melt season. In contrast, there has been an
increase in Antarctic sea ice, but with a smaller rate of
change than in the Arctic.
Snow cover is sensitive to changes in temperature, particularly during the spring, when the snow starts to melt.
Spring snow cover has shrunk across the northern hemisphere since the 1950s. IPCC AR5 concluded that it is likely
that snowfall events are decreasing in most regions (North
America, Europe, Southern and East Asia) where increased
winter temperatures have been observed (Hartmann et al.
2013). The total seasonal snowfall is reported to be declining
along with increase in maximum and minimum temperatures
in the western Himalaya. Confidence is low for changes in
snowfall over Antarctica.
Uptake of anthropogenic CO 2 by the ocean increases the
hydrogen ion concentration in the ocean water, causing
acidification. There is high confidence that the global average pH of the surface ocean has decreased by 0.1 pH units
since the beginning of the industrial era, corresponding to an
approximately 30% increase in acidity (Stocker et al. 2013).
1.2.2 Projected Changes in Global Climate
This section assesses projected long-term changes in the
global climate system during the twenty-first century. These
changes are expected to be larger than the internal variability
of the climate system and to depend primarily on how
anthropogenic emissions change the atmospheric composition in the future. Aerosol emissions are projected to decline
in the coming decades, and it is expected that future changes
will be dominated by the increasing concentrations of
GHGs.
Climate models are used to study the response of the
climate system to anthropogenic activity (also referred to as
‘external forcing’). Towards studying how the climate will
change in the twenty-first century, several standardized
scenarios have been developed, each with a specific
description of how human-induced changes would affect the
planet’s energy budget. Differences between scenarios are
based on underpinning assumptions about future changes in
fossil fuel consumption, land use change, etc., and were
developed using integrated assessment models that combined economic, demographic and policy modelling, with
simplified physical climate models in order to simulate the
global economic impacts of climate change under different
mitigation scenarios (Calel and Stainforth 2017).
Earth system models, developed by climate modelling
groups worldwide, perform climate change simulations for
these forcing scenarios, whose standardization facilitates
easy intercomparison between the results of these studies.
The scenarios used by models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that
contributed to the IPCC AR5 were termed the Representative Concentration Pathways (RCPs) and covered the period
from 2006 to 2100 (van Vuuren et al. 2011). The four RCPs
that were defined were the RCP2.6, representing a low
emissions pathway resulting in radiative forcing (RF) of
roughly 2.6 W/m
2 at the end of the twenty-first century,
RCP4.5 and RCP6 representing intermediate emission
pathways resulting in an RF of 4.5 W/m
2 and 6 W/m
2 ,
respectively and the high emissions scenario RCP8.5 representing a pathway with continued growth in GHG emissions leading to an RF of roughly 8.5 Wm
−2 at the end of the
twenty-first century. Various chapters of this report mainly
use the RCP pathways to study future changes in the climate
system.
The AR5 assessment concluded that GMST will continue
to rise over the twenty-first century with increasing GHGs.
The increase in GMST for 2081–2100, relative to 1986–
2005 will likely be in the 5–95% range of 0.3–1.7 °C under
RCP2.6 and 2.6–4.8 °C under RCP8.5 (Collins et al. 2013).
Assessment of precipitation based on CMIP5 models indicates that it is virtually certain that global mean precipitation
will increase by more than 0.05 mm day
−1 and 0.15 mm
day
−1 by the end of the twenty-first century under the
RCP2.6 and RCP8.5 scenarios, respectively (Collins et al.
2013). The median of the global mean sea-level rise for the
period 2081–2100 is 0.47 m in RCP4.5 and 0.63 m in the
1 Introduction to Climate Change Over the Indian Region
7
reversing the drying trend that occurred from the mid-1970s
to mid-1990s. Human influence has also contributed to
large-scale changes in precipitation patterns over land
(medium confidence; Bindoff et al. 2013). It is likely that,
since about 1950, the number of heavy precipitation events
over land has increased in more regions than it has decreased.
Local changes in temperature affect the cryosphere. The
amount of ice contained in glaciers globally has been
declining every year for over 20 years. Total ice loss from
the Greenland and Antarctic ice sheets during 1992–2011
(inclusive) has been 4260 [3060–5460] Gt, equivalent to
11.7 [8.4–15.1] mm of sea level. However, the rate of
change has increased with time and most of this ice has been
lost in the second decade of the 20-year period (Vaughan
et al. 2013).
The global average sea level rose by 19 cm from 1901 to
2010 (Stocker et al. 2013). The average rate of rise measured
by satellites has been 3.2 [2.9–3.5] mm/year since the 1990s
up from 1.7 [1.5–1.9] mm/year during the twentieth century,
obtained from historical tide gauge records (Hartmann et al.
2013). Thermal expansion and glacier melt because of
anthropogenic global warming have been the major drivers
of rise in global sea levels over the past century.
Substantial losses in Arctic sea ice have been observed
since satellite records began, particularly at the time of the
minimum extent, which occurs in September, at the end of
the annual melt season. In contrast, there has been an
increase in Antarctic sea ice, but with a smaller rate of
change than in the Arctic.
Snow cover is sensitive to changes in temperature, particularly during the spring, when the snow starts to melt.
Spring snow cover has shrunk across the northern hemisphere since the 1950s. IPCC AR5 concluded that it is likely
that snowfall events are decreasing in most regions (North
America, Europe, Southern and East Asia) where increased
winter temperatures have been observed (Hartmann et al.
2013). The total seasonal snowfall is reported to be declining
along with increase in maximum and minimum temperatures
in the western Himalaya. Confidence is low for changes in
snowfall over Antarctica.
Uptake of anthropogenic CO 2 by the ocean increases the
hydrogen ion concentration in the ocean water, causing
acidification. There is high confidence that the global average pH of the surface ocean has decreased by 0.1 pH units
since the beginning of the industrial era, corresponding to an
approximately 30% increase in acidity (Stocker et al. 2013).
1.2.2 Projected Changes in Global Climate
This section assesses projected long-term changes in the
global climate system during the twenty-first century. These
changes are expected to be larger than the internal variability
of the climate system and to depend primarily on how
anthropogenic emissions change the atmospheric composition in the future. Aerosol emissions are projected to decline
in the coming decades, and it is expected that future changes
will be dominated by the increasing concentrations of
GHGs.
Climate models are used to study the response of the
climate system to anthropogenic activity (also referred to as
‘external forcing’). Towards studying how the climate will
change in the twenty-first century, several standardized
scenarios have been developed, each with a specific
description of how human-induced changes would affect the
planet’s energy budget. Differences between scenarios are
based on underpinning assumptions about future changes in
fossil fuel consumption, land use change, etc., and were
developed using integrated assessment models that combined economic, demographic and policy modelling, with
simplified physical climate models in order to simulate the
global economic impacts of climate change under different
mitigation scenarios (Calel and Stainforth 2017).
Earth system models, developed by climate modelling
groups worldwide, perform climate change simulations for
these forcing scenarios, whose standardization facilitates
easy intercomparison between the results of these studies.
The scenarios used by models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) that
contributed to the IPCC AR5 were termed the Representative Concentration Pathways (RCPs) and covered the period
from 2006 to 2100 (van Vuuren et al. 2011). The four RCPs
that were defined were the RCP2.6, representing a low
emissions pathway resulting in radiative forcing (RF) of
roughly 2.6 W/m
2 at the end of the twenty-first century,
RCP4.5 and RCP6 representing intermediate emission
pathways resulting in an RF of 4.5 W/m
2 and 6 W/m
2 ,
respectively and the high emissions scenario RCP8.5 representing a pathway with continued growth in GHG emissions leading to an RF of roughly 8.5 Wm
−2 at the end of the
twenty-first century. Various chapters of this report mainly
use the RCP pathways to study future changes in the climate
system.
The AR5 assessment concluded that GMST will continue
to rise over the twenty-first century with increasing GHGs.
The increase in GMST for 2081–2100, relative to 1986–
2005 will likely be in the 5–95% range of 0.3–1.7 °C under
RCP2.6 and 2.6–4.8 °C under RCP8.5 (Collins et al. 2013).
Assessment of precipitation based on CMIP5 models indicates that it is virtually certain that global mean precipitation
will increase by more than 0.05 mm day
−1 and 0.15 mm
day
−1 by the end of the twenty-first century under the
RCP2.6 and RCP8.5 scenarios, respectively (Collins et al.
2013). The median of the global mean sea-level rise for the
period 2081–2100 is 0.47 m in RCP4.5 and 0.63 m in the
1 Introduction to Climate Change Over the Indian Region
7