India faces an unprecedented crisis due to climate change impacts, a government assessment report revealed last month, presenting a grim analysis of observed changes and future projections of warming impacts including precipitation changes, temperature rise, droughts, sea level rise and extreme weather events.
The ‘Assessment of Climate Change over the Indian Region- A Report of the Ministry of Earth Sciences, Government of India, is the first ever climate change report for India prepared by the Centre for Climate Change Research (CCCR) at the Indian Institute of Tropical Meteorology (IITM), Pune.
Noting that the global average temperature has risen by around 1 °C since pre-industrial times, the report stated that the magnitude and rate of warming cannot be explained by natural variations alone and must necessarily take into account changes due to human activities. The report also pointed out that warming since the 1950s has already contributed to a significant increase in extreme weather manifestations like heat waves, droughts and cyclones, changes in precipitation and wind patterns including shifts in the monsoon systems, warming and acidification of oceans, melting of sea ice and glaciers, rising sea levels, and changes in marine and terrestrial ecosystems.
The report mentioned the projected rise of global average temperatures by 5 °C or more by the end of the twenty-first century under current GHG emission rates and further added that even if all the Paris Agreement commitments were met, global warming will still exceed 3 °C by the end of the century. It is obvious that the world would need to go far beyond the Nationally Determined Contributions of the Paris Agreement to avoid catastrophic climate change. The global lockdown response to the COVID-19 pandemic gives us hope that such collective action is quite possible in this critical period.
Climate Change in India: Observed and Projected Changes
India is a vast country with many climate zones, and hence, local climate change and their causes can be quite complex. This assessment is the first attempt to document climate changes in different parts of India, observed changes and future implications for the different regions.
Temperature Rise Over India
India’s average temperature has risen by around 0.7 °C during 1901–2018. This rise in temperature is largely on account of GHG-induced warming, partially offset by forcing due to anthropogenic aerosols and changes in land use and land cover. By the end of the twenty-first century, the frequencies of occurrence of warm days and warm nights are projected to increase by 55% and 70%, respectively, relative to the reference period 1976-2005.
The frequency of summer (April–June) heat waves over India is projected to be 3 to 4 times higher by the end of the twenty-first century as compared to the 1976–2005 baseline period. The average duration of heat wave events is also projected to approximately double, but with a substantial spread among models. In response to the combined rise in surface temperature and humidity, amplification of heat stress is expected across India, particularly over the Indo-Gangetic and Indus River basins.
Indian Ocean Warming
Sea surface temperature of the tropical Indian Ocean has risen by 1 °C on average during 1951–2015, markedly higher than the global average warming of 0.7 °C, over the same period. Ocean heat content of the Indian Ocean has also exhibited an increasing trend over the past six decades (1955–2015), with the past two decades (1998–2015) having witnessed a notably abrupt rise. During the twenty-first century, sea surface temperature and ocean heat content in the tropical Indian Ocean are projected to continue to rise.
Changes in Rainfall
The summer monsoon precipitation (June to September) over India has declined by around 6% from 1951 to 2015, with notable decreases over the Indo-Gangetic Plains and the Western Ghats.
There has been a shift in the recent period toward more frequent dry spells (27% higher
during 1981–2011 relative to 1951–1980) and more intense wet spells during the summer
monsoon season. Over central India, the frequency of daily precipitation extremes increased by about 75% during 1950–2015.
With continued global warming and anticipated reductions in anthropogenic aerosol emissions in the future, projections include increase in the mean and variability of monsoon precipitation by the end of the twenty-first century, together with substantial increases in daily precipitation extremes.
The overall decrease of seasonal summer monsoon rainfall during the last 6–7 decades has led to an increased propensity for droughts over India. Both the frequency and spatial extent of droughts have increased significantly during 1951–2016. In particular, areas over central India, southwest coast, southern peninsula and north-eastern India have experienced more than 2 droughts per decade, on average, during this period. The area affected by drought has also increased by 1.3% per decade over the same period.
Climate model projections indicate a high likelihood of increase in the frequency (>2 events per decade), intensity and area under drought conditions in India by the end of the twenty-first century.
Sea Level Rise
Sea levels have risen globally because of the continental ice melt and thermal expansion of ocean water in response to global warming. Sea-level rise in the North Indian Ocean occurred at a rate of 1.06–1.75 mm per year during 1874–2004 and has accelerated to 3.3 mm per year in the last two and a half decades (1993–2017), which is comparable to the current rate of global mean sea-level rise.
At the end of the twenty-first century, sea levels in the same area are projected to rise by approximately 300 mm, compared to the projected global mean rise of approximately 180 mm.
There has been a significant reduction in the annual frequency of tropical cyclones over the North Indian Ocean basin since the middle of the twentieth century (1951–2018). In contrast, the frequency of very severe cyclonic storms during the post-monsoon season has increased significantly (+1 event per decade) during the last two decades (2000–2018).
However, a clear signal of anthropogenic warming on these trends has not yet emerged.
Climate models project a rise in the intensity of tropical cyclones during the twenty-first century.
Changes in the Himalayas
The Hindu Kush Himalayas (HKH) experienced a temperature rise of about 1.3 °C during
1951–2014. Several areas of HKH have experienced a declining trend in snowfall and also
retreat of glaciers in recent decades. In contrast, the high-elevation Karakoram Himalayas have experienced higher winter snowfall that has shielded the region from glacier shrinkage.
By the end of the twenty-first century, the annual mean surface temperature over HKH is
projected to increase by about 5.2 °C under the worst-case scenario. The projections also indicate an increase in annual precipitation, but decrease in snowfall over the HKH region by the end of the twenty-first century, with large spread across models.
Since the middle of the twentieth century, India has witnessed a rise in average temperature; a decrease in monsoon precipitation; a rise in extreme temperature and rainfall events, droughts, and sea levels; and an increase in the intensity of severe cyclones, alongside other changes in the monsoon system. There is compelling scientific evidence that human activities have influenced these changes in regional climate.
Human-induced climate change is expected to continue apace during the twenty-first century. To improve the accuracy of future climate projections, particularly in the context of regional forecasts, it is essential to develop strategic approaches for improving the knowledge of Earth system processes, and to continue enhancing observation systems and climate models.