Climate Change

The takeaway messages in the IPCC’s AR6: What does it mean for India?

Print edition : September 10, 2021

A farmer inspecting his banana plants that were damaged by the strong winds and heavy rainfall of cyclone Tauktae, at Chachegaon Village in Karad, Maharashtra, on May 18. After 2015, the Arabian Sea has witnessed more cyclones in the pre-onset and onset phase of the monsoon season. Photo: PTI

Personnel of that National and State Disaster Response Forces during a rescue operation on July 30, two days after a cloudburst caused flash floods at Hanzor in Kishtwar district of Jammu and Kashmir. Photo: PTI

Army personnel during a rescue operation on July 28 at Hanzor after the cloudburst. Changes in the cloud structure along the mountainous terrains of the Western Ghats and the Himalaya make these regions hotspots for mini cloudburst events. Photo: PTI/Photo made available by the Army

The uncertainty with regards to local sea level rise projections due to climate change will have serious implications for regions that are already below sea level such as Kuttanad (Alappuzha district) in Kerala. Here, after floods in Kuttanad in August 2018. Photo: Tibin Augustine/AP

From the IPCC’s Sixth Assessment Report, it is clear that the outlook is grim for India on the climate change front. It can expect to experience erratic monsoons, severe cyclonic storms in the pre- and post-monsoon seasons, heatwaves, and flash flood and drought events.

Since the inception of the Intergovernmental Panel on Climate Change (IPCC) in 1988, scientists have been issuing warnings about the likelihood of accelerating climate change, which have been ignored. From the First Assessment Report (AR1) published in 1990 to the AR5 in 2014, it has been emphasised that climate change is a challenge with global consequences that needs international cooperation. The Sixth Assessment Report (AR6) could not come up with any new information as it is “unequivocal” that in recent decades humans have caused the unprecedented changes in the climate, most of which are understood to be “inevitable” and “irreversible”.

It is evident and almost widely accepted that widespread and rapid changes have occurred in the atmosphere, cryosphere and biosphere and on land and in the oceans. The uncertainty about the possible outcomes of climate change is decreasing. Now that the science of climate change has matured, it is possible to say with a high level of confidence that global warming is an inconvenient truth. Nearly all of the earth’s surface has been warming in response to the increasing levels of greenhouse gases (GHGs) accumulating in the atmosphere mainly through anthropogenic activities. Specifically, the global average surface temperature of the earth has increased by roughly 1.1 degrees Celsius compared with the pre-industrial baseline period of 1850-1900, which is unprecedented in the last 2,000 years. Warming took place at a higher rate over land compared with the ocean, thanks to the increased heat capacity of ocean waters. Despite the reduction in carbon dioxide (CO2) emissions that occurred because of the lockdowns during the COVID-19 pandemic, the CO2 concentration in the atmosphere reached a record high of 419 parts per million this year, which the planet has never seen in past two million years.

There is plenty of evidence to show that the unmatched warming caused by the higher level of GHGs in the atmosphere is mainly due to human activities. However, nowadays numerical models are becoming a handy tool to evaluate the complex feedback between anthropogenic activities and global warming. The new-generation climate models include the physics behind greenhouse warming along with realistic representations of atmospheric dynamics, ocean processes, sea ice physics, changes in land use and land cover, and other physical processes shattering the climate and forcing it to change. Climate models are able to simulate the evolution of the earth’s climate over time on the basis of the physical principles governing the atmosphere and the oceans. Climate models were able to reproduce the observed rate of warming only when anthropogenic factors, GHG emissions in particular, were included along with natural climate forcings. The success of the climate models in simulating the climate of medieval periods has led to them to being used widely to predict all possible future scenarios, albeit with associated uncertainty. Moreover, their projections are what is in principle not the forecast for the future but different possible scenarios of carbon emissions based on assumptions that may or may not be realised and are hence subject to uncertainties. The models’ projections help policymakers take appropriate measures to reduce the impact of climate change and devise adaptation and mitigation measures for different expected future scenarios.

Also read: What is the IPCC and what does it do?

The AR6 is mostly derived from combinations of the latest generation of global coupled models produced as part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and updated estimates of climate sensitivity. The report describes an urgent climate emergency and is a wake-up call for the world to take immediate action. It also forms the base for the negotiations to begin in the coming Conference of Parties (COP 26) summit to be held in Glasgow in November.

RCPs and SSPs

The IPCC uses scenarios as a common tool to assess different forcings with respect to varying degrees of GHG warming that might occur in future situations in which outcomes are uncertain. In the previous assessment reports, the future scenarios were derived from different representative concentration pathways (RCPs) describing different levels of radiative forcing with respect to the varying future levels of GHGs without the socio-economic narratives connected to them even being considered. However, in the AR6, the new sets of scenarios have been derived by integrating a more realistic representation of socio-economic pathways (SSPs) with RCPs. These SSPs were developed by considering socio-economic aspects of population growth, economic growth, education, urbanisation and technological innovations. In a nutshell, RCPs and SSPs are complementary: the RCPs set the physical pathways of radiative forcing due to GHG emissions while the SSPs provide a more anthropogenic-centric framework to explore the interplay between different socio-economic conditions, policies, climate change impacts and the cost and challenges associated with adaptation and mitigation. These SSP scenarios range from a world with growth that is driven by sustainability and equality (that is, SSP1) to a world with rapid and unconstrained growth in economic output and energy use (that is, SSP5).

The most important part of the IPCC report says that even if we assume a middle-of-the-road scenario that poses a medium challenge to mitigation and adaptation, the more ambitious limit of 1.5 °C and the 2 °C warming target set by the Paris Agreement will be breached between 2030 and 2040 and 2050 and 2060 respectively. For intermediate emission scenarios, the warming will very likely be as high as 2.1 to 3.5 °C by 2100. In any case, global warming is going to hit 1.5 °C in the early 2030s irrespective of the low-, medium- or high-emission scenarios. That is, global warming will continue for some time even if all emissions are stopped. Assuming a 66 per cent chance of limiting global warming to 1.5 °C, only 360 billion tonnes of CO2 (GtCO2) remains in our carbon bucket, and this could be achieved in fewer than 10 years considering the current rate of increase of CO2 at 40-45 GtCO2/year. In this global scenario, there is little India can do considering its current contribution to the total carbon emissions is about 7 per cent, whereas China contributes 28 per cent. India’s per capita emission is also very low compared with the developed nations. However, India’s level of exposure to the associated direct impact of extreme weather events puts it in the top 10 of most vulnerable countries.

Extreme weather events

Although climate change is a global challenge, there are both global and local solutions for adaptation and mitigation. Climate scientists still believe that whatever the world has experienced so far in the form of extreme weather events are just trial runs and the worst is yet to come. There is a general consensus that climate change is often talked about in terms of surface temperature because it is a relatively easy parameter to measure and it is a pretty easy weather parameter to forecast. However, attributing climate change impacts on each and every weather extreme is rather difficult. It is easy to see that both the amplitude and frequency of the extreme weather events are increasing in direct relation to increasing global warming: More frequent hot extremes, marine heatwaves, heavy rainfall events, occurrences of hydrological and ecological droughts in some regions and floods in other regions or floods and droughts occurring in the same place and a changing proportion of intense tropical cyclones along with a reduction in Arctic sea ice, snow cover and permafrost. It is harder to follow that both extremes of hydrological conditions, that is, frequent floods and intermittent droughts, are becoming a more common affair in India. A warmer atmosphere holds more water vapour: there is a 7 per cent increase in water vapour–holding capacity with every 1 °C of atmospheric warming. More moisture in the atmosphere leads to more intense rain spells, but these rains do not necessarily do any good for either water resources or agriculture. Heavy rain received over a shorter period of time may lead to high run-off, which erodes soil and leaches nutrients at a faster rate. Certainly, it will lead to more flash floods in cities and poses a challenge to the current poorly planned drainage infrastructure in Indian cities.

Also read: Fires to floods: Extreme weather events worldwide

Along with the changes in rainfall intensity and distribution, changes in the cloud structure especially along the mountainous terrains of the Western Ghats and the Himalayan regions make these regions hotspots for mini cloudburst events. Mini cloudbursts are intense short spells of rain that may not exceed 10 centimetres in one hour, which is the classical definition of cloudburst by the India Meteorological Department. However, less intense rain spells with an intensity greater than 5 cm in two hours may cause flash floods and landslides along the slopes of the Western Ghat mountains and the Himalayan regions. Heavy rainfall of a short duration, especially from mesoscale mini cloudburst events, also brings run-off water beyond the carrying capacity of streams, and mid land regions of the west coast have often experienced flash floods.

The combined effects of cloudbursts, landslides and flash floods may get aggravated when they occur in areas where the land has been degraded because of human activities such as conversion of forest land to plantations and crop fields. The land degradation affects people, especially indigenous forest people (tribal), and the ecosystems connected to it. Hence, climate change exacerbates the ongoing land degradation process and introduces new patterns of degradation. Land degradation combined with climate change may adversely affect people’s livelihoods and poses new adaptation challenges and has profound implications for natural resource–based livelihood systems and social systems. On the other hand, land degradation processes such as deforestation may be considered another trigger for climate change as they increase emissions of GHGs and reduce the carbon uptake.

When we talk about climate change, more focus goes to extreme rainfall events. But there is another serious and silent killer: drought. Hotter temperatures due to global warming cause moisture to evaporate quickly from the ground, and when the land is already degraded, meteorological droughts easily get transformed into agricultural and hydrological droughts. Hence, drought-prone regions of central and western India will experience more severe drought conditions that may become chronic drought conditions. Certain regions of India may witness a swing between frequent floods and back-to-back drought conditions, and this may displace people. More importantly, the global water cycle will get accelerated, with increasing surface temperatures and heavy rainfall and surface water run-off.

India is considered “the land of monsoons”. The impact of global warming due to GHG emissions and the counteracting impact of aerosol loading and cloud albedo (reflectivity) feedback make it difficult to produce reliable projections of the monsoons. However, the IPCC report says with high confidence that the monsoons will become more erratic: the warmer climate will lead to prolonged wet and dry conditions, which will have possible implications for severe floods and prolonged drought conditions.

Also read: Landmark IPCC report provides a 'reality check' from scientists

However, the frequency and location of these events will depend on the projected changes in regional circulation patterns. With an expanding tropical belt and a reducing land-sea thermal contrast, the strength of the monsoon circulation may reduce but the associated reduction in rain can partly be offset by the warming-induced contribution to heavy precipitation events over the Indian region. Although, spatial and temporal variabilities are an inherent part of the Indian monsoon, there are preferred regions of deep clouds, especially over central India, north-eastern India and the northern parts of the Western Ghats. These are the potential breeding zones of cloudburst to mini cloudburst events, and under a warming climate, more and more regions in India will become prone to severe flash flood events. The atmospheric warming along with more aerosol loading and structural changes in deep clouds make the monsoon climate more prone to lightning hazards.

Heat extremes have already increased in India, and in recent decades, heatwave conditions have even extended to more southern latitudes. The IPCC report warns that almost 30 per cent of the days in a year may witness maximum temperatures above 35 °C under the 1.5 °C to 2 °C warming scenario, which may increase to 40-45 per cent for a 4 °C warming scenario. Human-induced global warming and increased urbanisation can even worsen the incidence of more severe heatwaves and heatstroke conditions. The urban heat island effect is a term to describe the higher temperature conditions over densely populated and highly developed urban areas compared with their rural counterparts. A rise in global temperatures in response to increased CO2 and other GHG emissions from anthropogenic activities can alter sweltering temperatures and result in an increase in the frequency, duration and intensity of heatwave events. The changes in land use and land cover due to human activities also modulate the incidence and severity of heatwaves.

The glacier run-off from high mountain ranges in the Asian region will increase in the early 21st century, and glacier mass is likely to decline further with a rise in temperature. As a result, rivers originating from the Himalayan ranges are expected to see flooding situations in the near future and may dry out when the glacier mass completely retreats in the far future. India recently witnessed landslide disasters due to a glacier breach in the Rishiganga region of Uttarakhand possibly caused by the combined effect of global warming and anthropogenic activities. Glaciers have a lagged response to temperature rise, so glacier retreat will continue even if temperatures stabilise. The report says that glaciers will lose between 18 per cent and 36 per cent of their early-21st-century mass under RCP2.6 and RCP8.5, respectively.

Changes in the oceans

The oceans are absorbing 93 per cent of the heat humans add to the atmosphere. As a result the sea surface temperature (SST) and the upper ocean heat content have increased in almost all ocean basins. The global SST is projected to increase further. This will lead to more frequent marine heatwave conditions. The fastest warming, the report says, has been observed in the northern Indian ocean, which includes the Arabian Sea and the Bay of Bengal. As surface waters warm, they get more stratified and the vertical exchange of water from the bottom to the top layers of the ocean is limited. The dissolved oxygen content in the upper ocean decreased by 0.5-3.3 per cent in the 1970-2010 period. This decreasing trend is more vigorous in the Arabian Sea, which could lead to adverse consequences for the productivity of its marine ecosystems. Deoxygenation enhances the release of nitrous oxide (N2O), methane (CH4) and CO2 from the ocean, says the report. The oceans have been absorbing 20-30 per cent of the CO2 emitted to the atmosphere, and this uptake leads to the reduction in the pH values of the ocean water and hence enhances the ocean acidification process. The connected ecological changes in the ocean may affect primary productivity and disturb the marine food web, and the consequent decline in fisheries will affect the livelihood of the indigenous fishing communities.

Also read: Climate tipping points are now imminent, scientists warn

Since 1901, the global mean sea level has risen by 0.2 m. By 2100, the global mean sea level is projected to rise by 0.38 m (in the range of 0.28-0.55 m) under a low-emission scenario and by an average of 0.77 m (in the range of 0.63-1.01 m) under a high-emission scenario. Since major contributors to sea level rise such as thermal expansion of sea water, mass loss from glaciers and ice sheets and changes in land water run-off are projected to increase in the future, we may reasonably assume that the sea level will continue to rise. Thermal expansion and glacial mass loss may each contribute nearly 40 per cent to the total sea level rise. However, uncertainty with regards to local sea level rise projection is large. This will have serious implications for regions that are already below sea level such as Kuttanad in Kerala.

The rise in SSTs and ocean heat content makes the northern part of the Indian Ocean, especially the Arabian Sea, a potential breeding ground for more and intense cyclonic systems. In recent decades, the average system count over the Arabian Sea has increased from two to three, and the cyclonic systems are intensifying. Recent studies suggest that the recent increasing frequency of extremely severe cyclonic storms over the Arabian Sea in the post-monsoon season is due to anthropogenic influences rather than natural variability. It has also been reported that dynamical and thermodynamical factors favourable for the production of more cyclones over the Arabian Sea in the pre-monsoon and post-monsoon seasons have been increasing in the recent epoch. For example, after 2015, the Arabian Sea has witnessed more cyclones (Ashoba, Mekunu, Sagar, Vayu, Nisarga, Tauktae, and so on) in the pre-onset and onset phase of the monsoon season. The recent severe cyclonic storms Nilofar, Chapala, Megh, Ockhi, Luban, Gaja, Kyarr and Maha are clear evidence of the increasing frequency of severe cyclonic storms over the Arabian Sea in the post-monsoon season. Most of the climate projection models now predict an intensification of tropical cyclones in a warmer climate without altering the total cyclone count. This again affects both the life and livelihood of coastal communities, and the resulting storm surge–induced water inundation will aggravate the sea level conditions all along India’s 7,000-km-long coastal belt.

Indian coastal cities are expected to be hit hard by compound events such as sea level rise, cyclone-induced storm surges and coastal erosion due to wind and wave activity combined with other development activities along the coast. Together with this, extreme rainfall events and higher river water run-off from the land will make most of the coastal regions around India more vulnerable in the future.

The worst impacts of climate change and global warming are going to hit those who are least able to adapt to them the hardest, that is, the poor and indigenous people who are more connected to the sea and the land for their livelihood. Unfortunately, indigenous people are often left out of the development agenda. We need to integrate indigenous knowledge with climate science to achieve the mitigation goals of climate change. This is the time to think about a paradigm shift from technology-based solutions to ecosystems-based approaches to achieve all the 17 Sustainable Development Goals.

S. Abhilash is the Director of the Advanced Centre for Atmospheric Radar Research, Cochin University of Science and Technology, Kerala.