Published on July 4 in Environmental Research Letters, a study led by the National Oceanography Centre (NOC) found flooding from rising sea levels could cost $14 trillion worldwide annually by 2100 if the target of holding increasing global temperatures within 2ºC of pre-industrial levels is missed.
However, the research also points out that based on varying scenarios and computer modeling, if governments miss the United Nations target – the extent of the costs could be much higher. The 2ºC target was agreed upon by 195 nations in Paris in 2015.
But the cuts in greenhouse gas (GHG) emissions promised by the UN Framework Convention on Climate Change are not yet enough to achieve the 2ºC limit, let alone a less stringent limit of 1.5°C, meaning deeper cuts will have to be made.
The research also found that upper-middle-income countries like China would see the largest increase in flood-related costs, while the highest income countries would suffer the least, simply because of existing high levels of coastal protection infrastructure.
The study’s lead author, Dr. Svetlana Jevrejeva, from the NOC, said: “More than 600 million people live in low-elevation coastal areas, less than 10 meters (33 feet) above sea level. In a warming climate, global sea level will rise due to the melting of land-based glaciers and ice sheets, and from the thermal expansion of ocean waters. So, sea level rise is one of the most damaging aspects of our warming climate.”
The methodology used in research
Sea level projections already exist for both emissions scenarios and socio-economic scenarios. However, no scenarios exist that cover limited warming below the 1.5°C and 2°C targets during the entire 21st century and further beyond that time.
So the research team explored the rate of global and regional sea level rise, along with the consequences of a restricted warming of 1.5ºC and 2ºC. They compared these results with sea level rise projections under unmitigated warming – using the emissions scenario Representative Concentration Pathway (RCP) 8.5.
Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its fifth Assessment Report (AR5) in 2014. They describe four possible climate futures, all of which are considered possible depending on how much greenhouse gases are emitted in the years to come.
The four climate futures include RCP2.6, RCP4.5, RCP6, and RCP8.5, and are named after a possible range of radiative forcing values in the year 2100 relative to pre-industrial values. In RCP 8.5, emissions continue to rise throughout the 21st century.
The researchers also used World Bank data on income groups (high, upper middle, lower middle, and low-income countries) to assess the impact of sea level rise on coastal communities from an economic perspective. They also used the Dynamic Interactive Vulnerability Assessment modeling framework for some individual countries.
The Dynamic Interactive Vulnerability Assessment modeling framework is a database that covers the world’s coasts, excluding Antarctica, and includes information on more than 80 physical, ecological, and socioeconomic parameters of the coastal zone.
Dr. Jevrejeva said: “We found that with a temperature rise trajectory of 1.5°C, by 2100 the median sea level will have risen by 0.52m (1.7ft). But, if the 2°C target is missed, we will see a median sea level rise of 0.86m (2.8ft), and a worst-case rise of 1.8m (5.9ft).”
“If warming is not mitigated and follows the RCP8.5 sea level rise projections, the global annual flood costs without adaptation will increase to US$ 14 trillion per year for a median sea level rise of 0.86m, and up to US$ 27 trillion per year for 1.8m. This would account for 2.8% of global GDP in 2100.”
“These results place further emphasis on putting even greater efforts into mitigating rising global temperatures.”
