<p class="title">The global sea level may be rising faster than previously thought, according to a study which suggests that the current measurement method underestimates the severity of the problem.</p>.<p class="bodytext">The research, published in the journal Science, questions the reliability of how sea levels rise in low-lying coastal areas such as southern Louisiana in the US is measured.</p>.<p class="bodytext">Relative sea-level rise, which is a combination of rising water level and subsiding land, is traditionally measured using tide gauges.</p>.<p class="bodytext">However, researchers from Tulane University in the US argue that in coastal Louisiana, tide gauges tell only a part of the story.</p>.<p class="bodytext">Tide gauges in such areas are anchored an average of 20 metres into the earth rather than at the ground surface.</p>.<p class="bodytext">"As a result, tide gauges do not record subsidence occurring in the shallow subsurface and thus underestimate rates of relative sea-level rise," said Molly Keogh, a PhD student at Tulane University.</p>.<p class="bodytext">"This study shows that we need to completely rethink how we measure sea level rise in rapidly subsiding coastal lowlands," said Torbjorn Tornqvist, a professor at Tulane University.</p>.<p class="bodytext">The study found that while tide gauges can accurately measure subsidence that occurs below their foundations, they miss out on the shallow subsidence component.</p>.<p class="bodytext">With at least 60 per cent of subsidence occurring in the top five metres of the sediment column, tide gauges are not capturing the primary contributor to relative sea-level rise.</p>.<p class="bodytext">An alternative approach is to measure shallow subsidence using surface-elevation tables, inexpensive mechanical instruments that record surface elevation change in wetlands.</p>.<p class="bodytext">Coastal Louisiana already has a network of more than 300 of these instruments in place.</p>.<p class="bodytext">The data can then be combined with measurements of deep subsidence from Global Positioning System (GPS) data and satellite measurements of sea-level rise, Keogh said.</p>.<p class="bodytext">Rates of relative sea-level rise obtained from this approach are substantially higher than rates as inferred from tide-gauge data.</p>.<p class="bodytext">"We, therefore, conclude that low-elevation coastal zones may be at higher risk of flooding, and within a shorter time horizon, than previously assumed," Keogh said.</p>.<p class="bodytext">She said the research has implications for coastal communities across the globe.</p>.<p class="bodytext">"Around the world, communities in low-lying coastal areas may be more vulnerable to flooding than we realised. This has implications for coastal management, city planners and emergency planners," Keogh said.</p>.<p class="bodytext">"They are planning based on a certain timeline, and if sea level is rising faster than what they are planning on, that is going to be a problem," she said.</p>
<p class="title">The global sea level may be rising faster than previously thought, according to a study which suggests that the current measurement method underestimates the severity of the problem.</p>.<p class="bodytext">The research, published in the journal Science, questions the reliability of how sea levels rise in low-lying coastal areas such as southern Louisiana in the US is measured.</p>.<p class="bodytext">Relative sea-level rise, which is a combination of rising water level and subsiding land, is traditionally measured using tide gauges.</p>.<p class="bodytext">However, researchers from Tulane University in the US argue that in coastal Louisiana, tide gauges tell only a part of the story.</p>.<p class="bodytext">Tide gauges in such areas are anchored an average of 20 metres into the earth rather than at the ground surface.</p>.<p class="bodytext">"As a result, tide gauges do not record subsidence occurring in the shallow subsurface and thus underestimate rates of relative sea-level rise," said Molly Keogh, a PhD student at Tulane University.</p>.<p class="bodytext">"This study shows that we need to completely rethink how we measure sea level rise in rapidly subsiding coastal lowlands," said Torbjorn Tornqvist, a professor at Tulane University.</p>.<p class="bodytext">The study found that while tide gauges can accurately measure subsidence that occurs below their foundations, they miss out on the shallow subsidence component.</p>.<p class="bodytext">With at least 60 per cent of subsidence occurring in the top five metres of the sediment column, tide gauges are not capturing the primary contributor to relative sea-level rise.</p>.<p class="bodytext">An alternative approach is to measure shallow subsidence using surface-elevation tables, inexpensive mechanical instruments that record surface elevation change in wetlands.</p>.<p class="bodytext">Coastal Louisiana already has a network of more than 300 of these instruments in place.</p>.<p class="bodytext">The data can then be combined with measurements of deep subsidence from Global Positioning System (GPS) data and satellite measurements of sea-level rise, Keogh said.</p>.<p class="bodytext">Rates of relative sea-level rise obtained from this approach are substantially higher than rates as inferred from tide-gauge data.</p>.<p class="bodytext">"We, therefore, conclude that low-elevation coastal zones may be at higher risk of flooding, and within a shorter time horizon, than previously assumed," Keogh said.</p>.<p class="bodytext">She said the research has implications for coastal communities across the globe.</p>.<p class="bodytext">"Around the world, communities in low-lying coastal areas may be more vulnerable to flooding than we realised. This has implications for coastal management, city planners and emergency planners," Keogh said.</p>.<p class="bodytext">"They are planning based on a certain timeline, and if sea level is rising faster than what they are planning on, that is going to be a problem," she said.</p>