PARIS, May 20: Massive extraction of groundwater can resolve a puzzle over a rise in sea levels in past decades, scientists in Japan said on Sunday.

Global sea levels rose by an average of 1.8 millimetres per year from 1961-2003, according to data from tide gauges.

But the big question is how much of this can be pinned to global warming.

In its landmark 2007 report, the UN's Nobel-winning Intergovernmental Panel on Climate Change (IPCC) ascribed 1.1mm per year to thermal expansion of the oceans — water expands when it is heated — and to meltwater from glaciers, icecaps and the Greenland and Antarctica icecaps.

That left 0.7mm per year unaccounted for, a mystery that left many scientists wondering if the data were correct or if there were some source that had eluded everyone.

In a study published in the journal Nature Geoscience, a team led by Yadu Pokhrel of the University of Tokyo say the answer lies in water that is extracted from underground aquifers, rivers and lakes for human development but is never replenished.

The water eventually makes it to the ocean through rivers and evaporation in the soil, they note.

Groundwater extraction is the main component of additions that account for the mystery gap, according to their paper, which is based on computer modelling.

“Together, unsustainable groundwater use, artificial reservoir water impoundment, climate-driven change in terrestrial water storage and the loss of water from closed basins have contributed a sea-level rise of 0.77mm per year between 1961 and 2003, about 42 percent of the observed sea-level rise,” it says.

The probe seeks to fill one of the knowledge gaps in the complex science of climate change.

Researchers admit to many unknowns about how the oceans respond to warming, and one of them is sea-level rise, an important question for hundreds of millions of coastal dwellers.

Just a tiny rise, if repeated year on year, can eventually have a dramatic impact in locations that are vulnerable to storm surges or the influx of saltwater into aquifers or coastal fields.

In its 2007 Fourth Assessment Report, the IPCC said the oceans would rise by between 18 and 59 centimetres by the century's end.

But this estimate did not factor in meltwater from the mighty Greenland and Antarctic ice sheets.

A study published last year by the Oslo-based Arctic Monitoring and Assessment Project (AMAP) said sea levels would rise, on current melting trends, by 90cms to 1.6 metres by 2100.—AFP

Opinion

One year on

One year on

Governance by the ruling coalition has been underwhelming and marked by growing authoritarianism.

Editorial

Climate funding gap
Updated 17 Feb, 2025

Climate funding gap

Pakistan must boost its institutional capacity to develop bankable climate projects.
UN monitoring report
Updated 17 Feb, 2025

UN monitoring report

Pakistan must press Kabul diplomatically over its tolerance of TTP terrorism.
Tax policy reform
17 Feb, 2025

Tax policy reform

THE cabinet’s decision to create a Tax Policy Office at the finance ministry has raised hopes that tax policy is...
Maintaining balance
Updated 16 Feb, 2025

Maintaining balance

It must take a more proactive approach to establishing Pakistan’s bona fides.
Welcome return
16 Feb, 2025

Welcome return

IT is almost here; the moment Pakistan has long been waiting for — the first International Cricket Council...
Childhood trauma
16 Feb, 2025

Childhood trauma

BEING a child in this society should not be so hard. But recurrent reports of child abuse — from burying girl...