Climate Change and Tipping Points
Unusually high temperatures on the west coast of North America, more violent tropical storms are just some indicators of climate change. What happens when changes become irreversible? Dr Anjani Ganase considers a few indicators of ecosystems approaching tipping point.
Tipping points are the environmental conditions beyond which an ecosystem can no longer cope with change. There is no going back when a tipping point is reached. The result is an irreversible shift to an alternative ecological state. Such shifts are usually associated with loss in biodiversity and changes in ecosystem services. Climate change drives unstable environmental conditions; and push organisms beyond their thresholds of tolerance; leading to mass die off and no recovery in a permanently transformed environment. Scientists are concerned about the global reach of climate change driving ecological tipping points that will permanently change the biomes that we depend on to survive.
The most well-known example of an ecosystem reaching tipping point is the mass die off of coral organisms which are extremely sensitive to warming ocean conditions; leading to algae dominated reefs. As corals are the major source of infrastructure on reefs, the loss of coral results in corresponding declines in marine biodiversity. It is projected that there will be up to 90 % coral loss by 2050 if the global average temperature is allowed to rise above 1.5 deg C. Global warming has already contributed to the die off of 50 % of the world’s coral reefs in the last thirty years. Even with the Paris Agreement targets, the average global temperature is expected to rise by 3 degrees by the end of the century.
What are some of the other large-scale tipping points that the world, mostly our children, might face if there is no significant reduction in carbon emissions? The idea of climate tipping points was introduced twenty years ago, however the likelihood of such tipping points being reached remained low even with a 4-5 degree global temperature rise. Now scientists have revisited the likelihood of such breaches at merely 2-3 degree rise in global temperature, with more damaging effects.
Loss of ice caps
In some regions of Antarctica, warming beyond a certain point can result in large-scale destabilization of the ice stored on land. Antarctica has the largest reserve of ice on land. Currently the Antarctic sea ice serves as a physical barrier preventing the ice stored on land from sliding into the ocean. As the ice melts away, a major tipping point will be reached when enough sea ice is removed and the ice attached to the land becomes unstable enough to result in the cascade of land ice into the ocean. Scientists project that such a phenomenon is likely to occur in about forty years. It is also expected that the rate of ice loss will rapidly increase after such an event - regardless of whether carbon dioxide emissions are reduced - owing to the unstable structure. Such rapid output of the ice to sea will significantly increase the rate of sea level rise by a factor of 10. A similar scenario is expected in Greenland at a more rapid rate. The higher rate of sea-level rise is a considerable threat to millions of people around the world who live in coastal areas.
The Amazon Tipping Point
Forests and wetlands house much of our carbon stores and slow the greenhouse effect (warming caused by certain gases in the atmosphere). At the same time, we also benefit from the services of forests and wetlands in the form of food, medicine and income. Unfortunately, deforestation for construction and farming is a major threat to the Amazon and to us. Researchers have estimated that a loss of 40 % through deforestation in the central, southern and eastern regions of the Amazon would result in diminished rainfall throughout the region causing longer dry seasons and the transition of forests to savanna plains. The Amazon rainforest regulates the rain cycle in the region supporting wildlife and human communities, and agriculture. Adding a warming climate to the mix, scientists originally estimated that a 4 degree rise in average global temperature would result in severe degradation of the Amazon rainforest through drought and fires. However, the threat is more dire considering the accelerated rate of deforestation and the current trajectory of climate change.
Cascading effects
As these major ecosystems shift, there will be cascading impacts on other ecosystems that are connected. The loss of the sea ice from Greenland would result in the sudden influx of fresh water into the North Atlantic Ocean. In the north Atlantic, cold, salty and dense ocean waters sink, driving surface currents such as the Gulf Stream. The massive influx of less dense fresh water in the north Atlantic will therefore slow the deep ocean currents of the Atlantic. The slowing of this current will impact the flow of the ocean currents in other parts of the world and impact weather conditions in regions across the planet. In our region, consider the impacts of El Niño and hurricanes. The threat of reaching tipping points should be enough to drive emergency climate action, especially considering the lives and livelihoods being affected. Such shifts mean that we may be thrust into uncharted alternative environmental states with different ecological parameters. Once the ball gets rolling, it’s near impossible to reverse.
In Trinidad and Tobago, we must be aware of the potential tipping points of the island ecosystems that we depend on. We have already seen most of the coral reefs throughout the Caribbean shift from coral dominant healthy reefs to algal dominance; Tobago is no exception. What about our forest ecosystems? How will our management or lack thereof affect or contribute to the shift in the functioning of our watersheds because of land clearing for development? How will this be exacerbated by a changing climate? We do not want to go into ecological unknowns. Think about the Northern Range and the Main Ridge Forest Reserve, and the roles they play in trapping the rain, regulating the temperatures of our rainforest island and preserving biodiversity of flora and fauna. Changes in these scenarios should not be entertained for they will affect agriculture and our ability to grow food, to collect potable water, to mitigate drought and fires.
Many ecosystem changes occur over decades. In our lifetimes, we are approaching tipping points within a few years. Unless we can dramatically reverse some of the causes of these changes, we might already be too late.
References
DeConto, R.M., Pollard, D., Alley, R.B. et al. The Paris Climate Agreement and future sea-level rise from Antarctica. Nature 593, 83–89 (2021). https://doi.org/10.1038/s41586-021-03427-0
Lovejoy, Thomas E., and Carlos Nobre. "Amazon tipping point." (2018): eaat2340
Lenton, Timothy M., et al. "Climate tipping points—too risky to bet against." (2019): 592-595.
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