Global sea levels have risen faster than previously thought over the past century, suggesting that climate change is having a greater-than-expected impact on the rising oceans, a study has found.
A new way of estimating global sea levels since the start of the 20th Century found that the period 1900-1990 experienced a 30 per cent smaller rise than researchers had previously calculated.
This would mean that since 1990 there has been a greater-than-expected acceleration in annual sea levels, with the annual rate of increase more than doubling compared to the preceding 90 years, the scientists found.
Until the age of satellites, sea levels were calculated mostly from readings of tide gauges unevenly dotted around the coastlines of the world.
However, this non-random distribution introduced an element of bias that overestimated sea level rise up to 1990, the researchers said.
Previous estimates suggested that the global mean sea-level rise over the 20th Century was between 1.5 and 1.8mms a year.
However the new estimate, based on a revised statistical analysis of the data, suggests the annual rate was about 1.2mm between 1900 and 1990 and about 3mm per year since 1990.
“What this [study] shows is that sea-level acceleration over the past century has been greater than had been estimated by others. It’s a larger problem than we initially thought,” said Eric Morrow of Harvard University.
Previously, researchers gathered tide gauge records from around the world, averaged them together for different regions and then averaged those rates together again to create a global estimate, Dr Morrow said.
“But these simple averages aren’t representative of a true global mean value. Tide gauges are located along coasts, therefore large areas of the ocean aren’t being included in these estimates and the records that do exist commonly have large gaps,” he said.
“Part of the problem is the sparsity of these records, even along the coastlines. It wasn’t until the 1950s that there began to be more global coverage of these observations, and earlier estimates of global mean sea-level change across the 20th Century were biased by that sparsity,” he explained.
In pictures: Changing climate around the world
In pictures: Changing climate around the world
Calved icebergs from the nearby Twin Glaciers are seen floating on the water in Qaqortoq, Greenland
Oroumieh, one of the biggest saltwater lakes on Earth, has shrunk more than 80 percent to 1,000 square kilometers in the past decade. It shrinks mainly because of climate change, expanded irrigation for surrounding farms and the damming of rivers that feed the body of water
A boat navigates among calved icebergs from the nearby Twin Glaciers in Qaqortoq, Greenland. Boats are a crucial mode of transportation in the country that has few roads. As cities like Miami, New York and other vulnerable spots around the world strategize about how to respond to climate change, many Greenlanders simply do what theyve always done: adapt. 'Were used to change, said Greenlander Pilu Neilsen. 'We learn to adapt to whatever comes. If all the glaciers melt, well just get more land
The Svalbard Global Seed Vault is seen after being inaugurated in Longyearbyen, Norway. The 'doomsday' seed vault built to protect millions of food crops from climate change, wars and natural disasters opened deep within an Arctic mountain in the remote Norwegian archipelago of Svalbard
A technician preparing to drain a vast underground lake at the Tete Rousse glacier on the Mont Blanc Alpine mountain, to avert a potentially disatrous flood. Some 65,000 cubic metres (2.3 million cubic feet) of water have gathered in a cavity, dangerously raising the pressure beneath the mountain, a favourite spot for holiday makers in Saint-Gervais-les-Bains
Cracked mud is picture at sunrise in the dried shores of Lake Gruyere affected by continuous drought near the western Switzerland village of Avry-devant-Pont. A leading climate scientist warned that Europe should take action over increasing drought and floods, stressing that some climate change trends were clear despite variations in predictions
Cattle graze on grassland that remains dry and brown at the height of the rainy season in south of Bakersfield, California. Its third straight year of unprecedented drought, California is experiencing its driest year on record, dating back 119 years, and dating back as far as 500 years, according to some scientists who study tree rings
An aerial view shows tents of flood-displaced people surrounded by water in southern Sehwan town. United Nations Framework Convention on Climate Change (UNFCCC) executive secretary Christiana Figueres met with people displaced by last year's devastating floods. Catastrophic monsoon rains that swept through the country in 2010 and affected some 20 million people, destroyed 1.7 million homes and damaged 5.4 million acres of arable land
An aerial view of flooding in North Wagga Wagga. Climate change is amplifying risks from drought, floods, storm and rising seas, threatening all countries but small island states, poor nations and arid regions in particular, UN experts warned
Damages caused by a landslide on the Pan-American highway near La Moramulca, 55 Km south of Tegucigalpa. International highways have been washed out, villages isolated and thousands of families have lost homes and crops in a region that the United Nations has classified as one of the most affected by climate change
A resident sprays water on a peatland fire in Pekanbaru district in Riau province on Indonesia's Sumatra island. Indonesia, an archipelago of 17,000 islands, is one of the world's biggest carbon emitters because of rampant deforestation. US Secretary of State John Kerry Sunday issued a clarion call for nations to do to more to combat climate change, calling it 'the world's largest weapon of mass destruction'
An excavator clearing a peatland forest area for a palm oil plantations in Trumon subdistrict, Aceh province, on Indonesia's Sumatra island. As Southeast Asia's largest economy grows rapidly, swathes of biodiverse forests across the archipelago of 17,000 islands have been cleared to make way for paper and palm oil plantations, as well as for mining and agriculture. The destruction has ravaged biodiversity, placing animals such as orangutans and Sumatran tigers in danger of extinction, while also leading to the release of vast amounts of climate change-causing carbon dioxide
Stagnant rain water with tannery waste make the Hazaribagh area in Old Dhaka as well as Buriganga River the most polluted. Each year during the seven-month long dry season between October and April the Buriganga River becomes totally stagnant with its upstream region drying up and becoming polluted from toxic waste from city industries
Waste water from Dhaka city drained to the River Buriganga contributes to its pollutions. On the World Water Day observed in 2007 under the theme Coping with Water Scarcity, under the leadership of the Food and Agriculture Organization of the United Nations, DrikNEWS explores some of the images of the river. UN-Water has identified coping with water scarcity as part of the strategic issues and priorities requiring joint UN action. The theme highlights the significance of cooperation and importance of an integrated approach to water resource management of water at international, national and local levels
Heavy smog has been lingering in northern and eastern parts of China, disturbing the traffic, worsening air pollution and forcing the closure of schools. China's Environment Ministry said it will send inspection teams to provinces and cities most seriously affected by smog to ensure rules on fighting air pollution are being enforced
Sea levels are rising through a combination of the thermal expansion of warmer seawater, the melting of glaciers and ice sheets and the faster run-off of freshwater from the land due to human irrigation projects.
The last report of the Intergovernmental Panel on Climate Change (IPCC) estimated that the average global rise in sea levels could be between 52cm and 98cm by 2100 for high CO2 emissions and between 28cm and 61cm for lower emissions.
This would mean that even if the world commits to lower greenhouse gas emissions under a new climate treaty, many coastal areas will still be seriously threatened by a sea-level rise of about half a metre by the end of this century – and further inevitable rises in subsequent centuries.
“We are looking at all the available sea-level records and trying to say the Greenland has been melting at this rate, the Arctic at this rate, the Antarctic as this rate and so on,” said Carling Hay of Harvard University, the lead author of the study.
“We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5mm to 1.8mm per year that other people had predicted,” Dr Hay said.
“But the math doesn’t work that way. Unfortunately, our new lower rate of sea-level rise prior to 1990 means that the sea-level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought,” she said.