Raghu Murtugudde and Roxy Mathew KollSep 27, 2019 17:49:10 IST
Editor's Note: This story is the second in a two-part series on a key report released by the United Nations on 25 September, the IPCC Special Report on Oceans and Cryosphere. Part One discusses the effects of climate change on glaciers, high mountains and the world's Third Pole, and projections for the future.
The United Nations climate change body IPCC just released a Special Report on Ocean and Cryosphere in a Changing Climate (SROCC), compiling new findings on Earth's water ecosystems and frozen reservoirs since the Panel released its Assessment Report 5 in 2014.
The report delves into how the world's oceans and the cryosphere are responding to global warming, with predictions for how they are projected to change in the near-term (2031-2050) and by the end of the century (2081-2100) in the different emission scenarios.
About 70 percent of the Earth's surface is covered by oceans, which contain 97 percent of all the water on Earth. This water is saline and not directly potable for humans. Oceans absorb well over 90 percent of the additional energy being trapped by anthropogenic greenhouse gas emissions and up to 30 percent of the carbon. Warming and acidifying oceans with rising sea levels pose severe challenges for the tropics and its the low-lying island states and a country like India whose lifeline, the summer monsoon, receives all its moisture from the ocean.
How have the oceans responded to the changing climate?
Oceans provide ecosystem services in terms of food, recreation, transportation, moisture source for the global hydrological cycle, etc. In the Indian Ocean, temperature, sea level and acidity are on a steady rise, with dissolved oxygen decreasing. Coral bleaching incidents are fairly common, and coastal wetlands like the Chillka lake/lagoon and Mumbai's coastline are facing more loss of vegetation, of habitats and changes in community and ecosystem structure. A loss of coastal blue carbon habitats like seagrass, mangroves and marshes that can also sequester (store) carbon has been detected in the Indian Ocean.
Anthropogenic global warming has increased the probability of post-monsoon tropical cyclones over the Arabian Sea. Cyclone Nilofar, for instance, was the first extremely-severe tropical cyclone to be recorded in the Arabian Sea in post-monsoon cyclone season in 2014. The cyclone didn't make landfall, but produced heavy rainfall in Western Indian coasts. With changes in many aspects of the Indian monsoons, extreme and widespread flooding, post-monsoon cyclones are adding more misery to the agricultural Rabi season (sown in winter, harvested in spring) in addition to the already-suffering Kharif season (monsoon crops).
Some apparent physical changes observed in the oceans include significant warming, loss of oxygen, acidification, sea ice loss and sea-level changes. From upper, intermediate and deep oceans to corals, coastal wetlands, kelp forests, mangroves, salt marshes, and seagrasses — all parts of the ocean ecosystems are running the gamut of signatures of global warming. There are already unwanted outcomes of global warming on ocean-human systems and ecosystem services ranging from drops in fisheries catch potentials, tourism and transportation impacts, and carbon uptake by oceans, which mitigates global warming but increases the oceans' acidity.
Diminished food security for human & marine life
Another severe impact of climate change in the Tropics is primary production.
Marine life and fisheries are sensitive to extreme heat events and oxygen drops as temperature rises. The main process that brings about these consequences is surface warming and increased stratification (formation of separate layers) making it harder for colder waters and nutrients from below to be brought to the surface. This increased stratification has already been shown to cause ocean desertification in the Indian Ocean, with potentially dire consequences for food security and geopolitical instabilities in the region, with spinoff global consequences of its own.
Warming and deoxygenation will also lead to increases in harmful algal blooms and pathogens such as vibrio cholera. Many of the species will either fail to adapt or be weakened in their functionality or migrate poleward leaving the tropics highly vulnerable in terms of marine ecosystem services. Warmer temperatures, especially extreme heat events will also increase the disease pressure on marine biota.
Polar ice cover and glaciers
Loss of snow cover, melting Arctic ice, sheets of melting ice breaking off Greenland and Antarctic glaciers are some of the negative impacts that we can already see unfolding in the polar latitudes. This has also clearly affected sea levels around the world, posing various challenges for tropical countries. Tropical monsoons also appear to be affected by climate change, due to changes in the higher latitude cryosphere.
Also expected to slow down as a result of climate change is the so-called Atlantic Meridional Overturning Circulation or AMOC. This movement causes the cold-saline heavy waters in the North Atlantic to sink, flow deep southward into the Southern Ocean, eventual surfacing in the Indian and Pacific Oceans before flowing back to the North Atlantic.
This circulation occurs over hundreds of years and is critical for the uptake of heat and carbon by oceans. The Indian Ocean warming was found to also contribute to irregularities in AMOC (the circulation was accelerated instead of slower due to global warming). This raises further concerns about the feedback between polar and Indian ocean responses to global warming and their net impact on the Indian monsoon. A poster child for ocean heatwaves, "the Blob" just returned to the northwest Pacific Ocean and is expected to wreak havoc on the ecosystem and have various weather and climate impacts on the US west coast.
Warm-water corals are already responding severely to warming and acidification in oceans, which are expected to continue. Novel conservation strategies to save corals, that are withering under warming, may come from looking into corals that appear to be thriving in warming waters, at what genetic characteristics may have yielded this adaption.
The impact of global warming on El Niño and La Niña remains to be fully understood but adaptation strategies must hedge their bets against an increase in extremes in both of them. The interactions of these modes with the global monsoon remain equally uncertain and must be better understood with regional monitoring and modelling.
While no abrupt and irreversible changes are expected in the Tropics, serious attention does need to be devoted to governance structures that respond to trans-boundary issues in the region. Similar structures also need to be put in place to govern shared resources of fisheries, transportation, hydropower, river waters, mangroves, salt marshes, seagrasses and such.
Projections for mitigation and adaptation
The report's novelty lies in the near-term projections that are laid out for the period 2031-2050. This is key data to help decision-making for humankind in climate change matters.The horizon for socio-economic and infrastructure decisions tend to be on the order of decades, making the near-term projections a useful tool to serve world leaders making important decisions on oceans and/or the cryosphere. The added projections for ocean acidification and dissolved oxygen are critical for decisions on vulnerable ecosystems that comprise fisheries, aquaculture and mangroves, salt marshes and seagrasses.
The bad news is that humanity is already on the high-emission path. The low-emission path is nearly unattainable without deft use of active carbon capture and storage technology, considering the rate of emissions and accumulating carbon in the atmosphere. Unsurprisingly, the high-emission (RCP8.5) scenario has much worse outcomes for global warming, ocean warming, deoxygenation, acidification and ocean extremes with significant, increasingly cryosphere loss and sea-level rise.
Regional projections for India and the Tropics
Based on the SROCC report, India and the tropics thus need to generate local projections using their own monitoring and modelling systems for the ocean and cryosphere. This is because the report's predictions don't offer region-specific data on the ocean and cryosphere, nor the uncertainties in the projections at regional scales.
This is summary too focuses on the broader context of the projections relevant for India and the Tropics. India and other countries in this belt stand to gain in geopolitical stability and continued economic growth by leading a regional coalition to address climate. Regional cooperation for long-term observations and modelling for changes in the ocean and cryosphere will also go a long way.
Understanding ocean processes & predictions for India and the Tropics
The Tropics (and India, in particular) must devote its attention to the lack of long-term, sustained Indian and Pacific ocean observations, climate model limitations in simulating variability and inter-ocean links to help render future projections less reliable than necessary for many of the adaptation decisions. Tropical cyclones, marine heatwaves, El Niño and La Niña events and other extremes will strain the resources and decision-making abilities of the tropical countries.
Regional and global responses need to be synergised with local needs and decisions in frameworks such as the UN’s Sustainable Development Goals. This will ensure climate-resilient development pathways for the oceans and cryosphere. Barriers to adaptation actions within the country and across the borders can come from institutional, socio-cultural and economic among others.
The report lists strategies for achieving climate-resilience via socioeconomic and ecological resilience keeping in mind the social, political and policy settings in which these strategies need to be implemented. The climate change impact mitigation and adaptation portfolio for the oceans and cryosphere include energy, carbon storage, pollution reduction, coastal vegetation, open ocean production and ocean acidification, as well as policies and governance that will demand adaptation of infrastructure to the ecosystem itself.. Relocating people and economic activities may also become essential in extreme cases.
All these actions will need the creation of new knowledge to sustainably navigate the future security of oceans and the cryosphere. The report emphasises the need to respect the local and indigenous knowledge in co-producing new knowledge for managing the shared resources and local and global commons. The report also notes that environmental change tends to exacerbate psychological distress, a phenomenon called solastalgia. This is a variant of homesickness brought about by changes in the environment people have lived in for a considerable amount of time.
India's National Climate Change Action Plan, which is currently still being drafted, does include a gameplan to sustain the Himalayan ecosystem. But marine resources, sea-level rise, mangroves, seagrasses, salt marshes, etc. can't be ignored. India's work is cut out for herself. She needs to balance her economic ambitions with climate resilience as the surrounding oceans and its unique cryosphere face multiple cascading impacts under global warming.
Roxy Mathew Koll is a climate scientist at the Indian Institute of Tropical Meteorology in Pune and a lead author of the IPCC Special Report on Oceans and the Cryosphere. Raghu Murtugudde is a professor of Atmospheric and Oceanic Science and Earth System Science at the University of Maryland. He is currently a visiting professor at IIT Bombay.
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