An increase in sea level is unavoidable

admin November 5, 2021
Updated 2021/11/05 at 7:44 AM

Working Group I of the Intergovernmental Panel on Climate Change (IPCC) Assessment Report, ‘Climate Change 2021: The Physical Science Basis,’ was just released, and it is a clarion cry for climate action. It is one of the most comprehensive scientific assessments of climate change research and effects available.

The study examines five possible future shared socioeconomic paths with differing amounts of greenhouse gas (GHG) emissions. The following are the scenarios depicted: inter-mediate GHG emissions; high and very high emissions, which are double the current levels by 2100 and 2050, respectively. very low and low GHG emissions, where emissions decline to net zero around or after the middle of the century, beyond which emissions are net negative; very low and low GHG emissions, where emissions decline to net zero around or after the middle of the century, beyond which emissions are net negative; very low and low GHG emissions, where emissions decline to net zero around or after the middle of the century, beyond Even under the middle scenario, average warming will almost certainly surpass 2°C by mid-century. The average world temperature is now 1.09°C higher than pre-industrial levels, while CO2 levels in the atmosphere are already 410 parts per million, up from 285 parts per million in 1850.

The study was put together by over 200 experts from several climatic disciplines who assessed the evidence and the uncertainties. They provide a range of confidence levels (a qualitative assessment of the results’ validity) from extremely low to very high. They also evaluate probability, which is stated probabilistically based on observations or modelling findings and is a quantifiable measure of uncertainty in a conclusion.

Potential risks for coastal cities

Coastal cities are home to over 700 million people globally, and there are ongoing plans to expand them. As a result, comprehending the threats posed by climate change and sea-level rise in the twenty-first and twenty-second centuries is critical. Because oceans react slowly to heat, sea-level rise will continue after emissions decline. Even in low-emission scenarios, the centennial-scale irreversibility of sea-level rise has consequences for the future.

The expansion of warm ocean waters, the melting of land glaciers, and the melting of ice sheets in Greenland and Antarctica are the primary causes of sea-level rise. Between 1901 and 2018, the global mean sea level (GMSL) increased by 0.2m. From 1901 to 1971, the average annual rate of sea-level rise was 1.3 millimeters per year, increasing to 3.7 millimeters per year (2006-2018). While thermal expansion was the primary cause of sea-level rise in the past century, glaciers and ice sheet melt are now major contributions. GMSL is projected to be 0.19m in 2050 and 0.44m by 2100 under the low emissions scenario. GMSL is projected to be about 0.23m in 2050 and 0.77m in 2100 under the extremely high emissions scenario. These increases are in comparison to 1995-2014 and do not account for ice sheet process uncertainty. Ice sheet models are used by scientists to forecast future glacier melt. While these models have evolved throughout time, they still contain gaps in their understanding and depiction of physical processes.

Major concern

As the ocean warms, ice sheets may quickly destabilise (marine ice sheet in-stability or MISI). In a similar mechanism, ice cliffs may fall quickly, causing fast sea-level rise; this is known as marine ice-cliff instability (MICI). MICI occurrences are not included in the above-mentioned sea level predictions since such shifts are difficult to model.

Changes in ice-ocean interactions, as Siegert et al. point out, may result in widespread and fast sea-level rise. This is caused by the abrupt disintegration of ice shelves (ice that flows into frigid seas while connected to the land). Ice shelves become susceptible to severe warming scenarios, resulting in MISI. Sea level rise may be as high as 1.61m by 2100 under the extremely high emissions scenario, with poor confidence (and in the 17th-83rd percentile range).

It’s thus difficult to construct probabilistic future scenarios using ice sheet and ocean models together. The models fail to account for the sudden and non-linear dynamical changes that occur. There is a high-end narrative in the study that involves procedures that are unclear. The key question is when, not if, the high-end scenario will materialise. Sea level rise of up to 2.3 meters by 2100 is not ruled out, according to projections based on “organised expert opinions.”

According to the UN Environment Programme’s Emissions Gap Report, the globe is on track to warm by more than 3°C this century, more than twice the Paris Agreement’s target. Sea-level predictions for warming over 3°C are also fraught with uncertainty.

India’s vulnerability

Sea-level rise and storms will grow more severe and frequent, putting communities along India’s coast at risk. Storm surges, severe rain, and floods will accompany them. Even the 0.1m to 0.2m increase anticipated in the next several decades with India may result in regular coastal floods. A speculator may believe that if sea levels rise by less than a meter by 2100, they’ll have another 60-80 years to continue building infrastructure along the shore. However, it is not the correct way to analyse the IPCC data.

The uncertainty about a metre or more of sea-level rise before 2100 is due to a lack of information and the inability to run accurate models. Low confidence does not rule out the possibility of greater sea-level rise. The low confidence in this instance stems from unknowns, such as a lack of data and the challenge of accurately modelling these processes in models. Ignoring the unknowns may lead to disaster. Coastal regulation, which should be tougher, not taxes, as it has been with each amendment of the Coastal Regulation Zone, should be included in adaptation to sea-level rise. Speculators should not be insured or bailed out by the government, coastal communities should be warned in advance and protected during severe weather events, natural and other barriers should be considered in a limited way to protect certain vulnerable areas, and retreat should be part of some very low-lying areas’ adaptation strategies.

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