Recently published Intergovernmental Panel on Climate Change (IPCC) Assessment Report from Working Group I – ‘Climate Change 2021: The Basis of Physics’ – Is A clarion call for climate action. It provides one of the most comprehensive scientific reviews on the science and effects of climate change.
The report discusses five different shared socio-economic paths to the future with varying levels of greenhouse gas (GHG) emissions. Illustrated scenarios are the following: very low and low GHG emissions, where emissions drop to near zero around the middle of the century or later, after which emissions are net negative; intermediate GHG emissions; High and very high emissions where they are twice the current levels by 2100 and 2050 respectively. Even in the intermediate scenario, there is a high probability that near mid-century average warming will exceed 2°C. The mean global temperature is already 1.09 °C above pre-industrial levels and the CO2 concentration in the atmosphere is currently 410 ppm compared to 285 ppm in 1850.
More than 200 experts working in many areas of climate have put together the report by assessing the evidence and uncertainties. They express their confidence levels (a qualitative measure of the validity of the findings) as very low to very high. They also measure probability (a quantitative measure of uncertainty in a finding) that is expressed as probabilities based on observations or modeling results.
come hell or high water
Around 700 million people live along the coast worldwide, and there are plans for expansion of coastal cities. Therefore, it is important to understand the risks associated with climate change and sea level rise in the 21st and 22nd centuries. Sea levels will continue to rise even after emissions have not increased, as the oceans slowly respond to warming. The century-scale irreversibility of sea level rise has implications for the future even under low emissions scenarios.
Sea level rise is mainly caused by the expansion of warm ocean waters, the melting of glaciers on land, and the melting of ice sheets in Greenland and Antarctica. The global mean sea level (GMSL) rose by 0.2 meters between 1901 and 2018. The mean rate of sea level rise was 1.3 mm/year (1901–1971) and increased to 3.7 mm/year (2006–2018). While sea level rise in the last century was mainly due to thermal expansion, glacier and ice sheet melting is now a major contributor.
In the low emission scenario, the GMSL is expected to be 0.19m in 2050 and 0.44m by 2100. In the very high emissions scenario, GMSL is expected to be around 0.23m in 2050 and 0.77m in 2100. These increases are relative to 1995. -2014 and exclude uncertainties in ice sheet processes.
Scientists rely on ice sheet models to predict future glacier melting. While these models have improved over the years, there are shortcomings in the knowledge and representation of physical processes.
uncertainties
Ice sheets can become increasingly unstable as water gets warmer (sea ice sheet instability or MISI). Ice caps can rapidly collapse in a related process, causing rapid sea level rise; This is sea ice reef instability (MICI). Such changes are difficult to model and MICI events are not included in the sea level estimates outlined above.
As Siegert et al. Indicated, changes in ice-ocean interactions could lead to widespread and rapid sea level rise. This results from the mass loss of ice shelves (ice that flows into cold oceans while attached to land), which can suddenly disintegrate. Under strong warming scenarios, ice shelves weaken and lead to MISI. In very high emissions scenarios, with low confidence (and in the 17th-83rd percentile range), sea level rise could be as high as 1.61m by 2100.
It is difficult to use ice sheet models in conjunction with ocean models to create probabilistic scenarios for the future. The models do not capture the sudden and non-linear dynamics of the changes that occur. The report has a high-end story that includes processes where there is uncertainty. The main uncertainty lies in the ‘when’ rather than ‘if’ being the high-end scenario. Estimates based on ‘structured expert decisions’ indicate that sea level rise of up to 2.3 m cannot be ruled out by 2100.
According to the United Nations Environment Program Emissions Gap Report, the world is headed for a temperature rise above 3°C this century, twice the Paris Agreement aspiration. And there is deep uncertainty in sea level projections for warming above 3 °C.
vulnerability in india
Coastal communities in India are vulnerable to sea level rise and storms, which will become more intense and frequent. They will be accompanied by storms, heavy rains and floods. Even with India expected to increase by 0.1 m to 0.2 m in the next few decades, it can lead to frequent coastal flooding. A speculator might think that if a sea level rise of less than a meter is the likely scenario by 2100, they would have another 60-80 years to continue infrastructure development along the coast. However, this would not be the correct way to interpret IPCC data.
Uncertainty about sea level rise of one meter or more before 2100 is related to a lack of knowledge and an inability to run models with the required accuracy. Low confidence does not mean that findings of higher sea level rise should not be relied upon. In this case, the low confidence is from the unknown – poor data and the difficulty of representing these processes well in the model. Ignoring strangers can prove to be dangerous.
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Adaptation to sea level rise should include a range of measures, along with coastal regulation, which should be stricter, not looser, as it has become with each update of the coastal regulation zone. The government should not insure or protect speculators, coastal communities should be alerted in advance and protected during severe weather events, natural and other barriers to be considered in a limited way to protect some vulnerable areas Should, and retreat should be part of adaptation strategies. For some very low-lying areas.
Sujatha Byrawan is a scientist who studies science, technology and policy.
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