Key Messages
• Annual mean, maximum and minimum temperatures
averaged over India during 1986–2015 show significant
warming trend of 0.15 °C, 0.15 °C and 0.13 °C per
decade, respectively (high confidence), which is consistent with dendroclimatic studies.
• Pre-monsoon temperatures displayed the highest warming
trend followed by post-monsoon and monsoon seasons.
• The frequency of warm extremes over India has increased
during 1951–2015, with accelerated warming trends
during the recent 30 year period 1986–2015 (high confidence). Significant warming is observed for the warmest
day, warmest night and coldest night since 1986.
• The CORDEX mean surface air temperature change over
India for the mid-term (long-term) period 2040–2069
(2070–2099) relative to 1976–2005 is projected to be in
the range of 1.39–2.70 °C (1.33–4.44 °C) across greenhouse gas warming scenarios. The ranges of these Indian
mean temperature trends are broadly consistent with the
CMIP5 based estimates.
• The frequency and intensity of warm days and warm
nights are projected to increase over India in the next
decades, while that of cold days and cold nights will
decrease (high confidence). These changes will be more
pronounced for cold nights and warm nights.
• The pre-monsoon season heatwave frequency, duration,
intensity and areal coverage over India are projected to
substantially increase during the twenty-first century
(high confidence).
2.1 Introduction
Temperature is an essential climate quantity that directly
affects human and natural systems. The global mean surface
temperature is a key indicator of climate change because it
increases quasi-linearly with cumulative greenhouse gas
emissions as documented in multiple assessment reports of
the Intergovernmental Panel on Climate Change (IPCC)
including the most recent Fifth Assessment Report (AR5;
IPCC 2013). This chapter assesses observed and projected
changes in the mean and extreme temperature over India.
The surface air temperature, typically measured at 2 m
above the ground, varies from one region to another within
India. This temperature also fluctuates naturally in interannual and decadal time scales in the background of
human-induced changes in the climate. One of the important
contributors of the observed changes in temperature not
caused by human activities is the natural internal climate
variability, which refers to the chaotic short-term fluctuations around the mean climate over a region or at a location.
This includes phenomena such as the variability in the El
Nino–Southern Oscillation (ENSO). The presence of internal
variability places fundamental limits on the accuracy with
which future temperature can be projected. The internal
variability becomes larger when averaging results over
smaller areas, which may lead to larger uncertainty in projections at the Indian country scale, relative to that at a
global scale (Collins et al. 2013).
The temperature projections are obtained by driving climate models with different future forcing scenarios. These
projections include the response of the climate system to
external forcing (e.g. changing greenhouse gas concentrations), internal variability and uncertainties associated with
differences between models. The multi-model ensemble
mean averages out the internal variability and model differences to a large extent and provides an estimate of the
response of the climate system to forcing.
2.2 Observed Temperature Changes Over
India
A significant observed warming trend in all India averaged
annual mean surface air temperature for the long-term period
1901–2010 was assessed using the estimates derived from
the India Meteorological Department (IMD) gridded
monthly station data (Srivastava et al. 2017). This assessment also documented several past studies which reported
the variability and trends in temperature over India. In this
section, the observed temperature changes over India for the
more recent three decades between 1986 and 2015 are
assessed using the estimates derived from the IMD gridded
daily station data.
2.2.1 Mean Temperature
The mean temperature over India has warmed from the
mid-twentieth century (Fig. 2.1), with an increased rate of
warming of 0.15 °C, 0.15 °C and 0.13 °C per decade for the
annual mean, maximum and minimum temperatures,
respectively, between 1986 and 2015 (Table 2.1).
The warming is not uniform across the seasons, with
considerably more warming in the pre-monsoon season
(March–May; MAM) than in other seasons. The rate of
warming of 0.26 °C, 0.29 °C and 0.20 °C per decade for the
pre-monsoon season mean, maximum and minimum temperatures, respectively, between 1986 and 2015 are relatively higher than that for the respective annual values (see
22
J. Sanjay et al.
• Annual mean, maximum and minimum temperatures
averaged over India during 1986–2015 show significant
warming trend of 0.15 °C, 0.15 °C and 0.13 °C per
decade, respectively (high confidence), which is consistent with dendroclimatic studies.
• Pre-monsoon temperatures displayed the highest warming
trend followed by post-monsoon and monsoon seasons.
• The frequency of warm extremes over India has increased
during 1951–2015, with accelerated warming trends
during the recent 30 year period 1986–2015 (high confidence). Significant warming is observed for the warmest
day, warmest night and coldest night since 1986.
• The CORDEX mean surface air temperature change over
India for the mid-term (long-term) period 2040–2069
(2070–2099) relative to 1976–2005 is projected to be in
the range of 1.39–2.70 °C (1.33–4.44 °C) across greenhouse gas warming scenarios. The ranges of these Indian
mean temperature trends are broadly consistent with the
CMIP5 based estimates.
• The frequency and intensity of warm days and warm
nights are projected to increase over India in the next
decades, while that of cold days and cold nights will
decrease (high confidence). These changes will be more
pronounced for cold nights and warm nights.
• The pre-monsoon season heatwave frequency, duration,
intensity and areal coverage over India are projected to
substantially increase during the twenty-first century
(high confidence).
2.1 Introduction
Temperature is an essential climate quantity that directly
affects human and natural systems. The global mean surface
temperature is a key indicator of climate change because it
increases quasi-linearly with cumulative greenhouse gas
emissions as documented in multiple assessment reports of
the Intergovernmental Panel on Climate Change (IPCC)
including the most recent Fifth Assessment Report (AR5;
IPCC 2013). This chapter assesses observed and projected
changes in the mean and extreme temperature over India.
The surface air temperature, typically measured at 2 m
above the ground, varies from one region to another within
India. This temperature also fluctuates naturally in interannual and decadal time scales in the background of
human-induced changes in the climate. One of the important
contributors of the observed changes in temperature not
caused by human activities is the natural internal climate
variability, which refers to the chaotic short-term fluctuations around the mean climate over a region or at a location.
This includes phenomena such as the variability in the El
Nino–Southern Oscillation (ENSO). The presence of internal
variability places fundamental limits on the accuracy with
which future temperature can be projected. The internal
variability becomes larger when averaging results over
smaller areas, which may lead to larger uncertainty in projections at the Indian country scale, relative to that at a
global scale (Collins et al. 2013).
The temperature projections are obtained by driving climate models with different future forcing scenarios. These
projections include the response of the climate system to
external forcing (e.g. changing greenhouse gas concentrations), internal variability and uncertainties associated with
differences between models. The multi-model ensemble
mean averages out the internal variability and model differences to a large extent and provides an estimate of the
response of the climate system to forcing.
2.2 Observed Temperature Changes Over
India
A significant observed warming trend in all India averaged
annual mean surface air temperature for the long-term period
1901–2010 was assessed using the estimates derived from
the India Meteorological Department (IMD) gridded
monthly station data (Srivastava et al. 2017). This assessment also documented several past studies which reported
the variability and trends in temperature over India. In this
section, the observed temperature changes over India for the
more recent three decades between 1986 and 2015 are
assessed using the estimates derived from the IMD gridded
daily station data.
2.2.1 Mean Temperature
The mean temperature over India has warmed from the
mid-twentieth century (Fig. 2.1), with an increased rate of
warming of 0.15 °C, 0.15 °C and 0.13 °C per decade for the
annual mean, maximum and minimum temperatures,
respectively, between 1986 and 2015 (Table 2.1).
The warming is not uniform across the seasons, with
considerably more warming in the pre-monsoon season
(March–May; MAM) than in other seasons. The rate of
warming of 0.26 °C, 0.29 °C and 0.20 °C per decade for the
pre-monsoon season mean, maximum and minimum temperatures, respectively, between 1986 and 2015 are relatively higher than that for the respective annual values (see
22
J. Sanjay et al.