first published as Shepherd on Climate No.50 on Sunday 11th November 2007.
Dr Nils-Axel Mörner had just stepped down after four years as President of the International Commission on Sea Level Changes when he was invited to attend a high-level international seminar in Moscow on climate change on 7 & 8 July 2004, chaired by Russian President Putin’s chief economic adviser, Alexander Illarionov, and attended by leading scientists from around the world.
Mörner was a Professor of Geology at the University of Stockholm with 30 years of experience studying sea level changes around the world.  He had been a lead reviewer on the 2001 Assessment Report of the UN’s Intergovernmental Panel on Climate Change (IPCC).
Later he was to remark that when appointed he had been astonished to discover that only one of the 22 authors of the section on sea levels was recognised as a genuine sea level expert.
Mörner had led a team to the Maldives and had concluded after extensive field observations that sea levels had fallen by between 20 and 30 centimetres in the 1970s and remained stable ever since. IPCC’s tide gauge data, however, showed sea level in the Maldives to be rising.
At the Moscow Seminar Mörner asked why the graph produced by the computer model favoured by the IPCC, based on Topex/Poseidon satellite data, had shown sea levels to be roughly stable until 2003, but had then been republished by the IPCC, using the same data, to show a pronounced upward ‘tilt’. According to Mörner the IPCC explanation for this ‘correction’ was that it was to take account of new data from tide gauges.
Mörner, like most experts, was wary of tide gauges because their data could be affected by rises or falls in the land on which they were sited. Land in the south-east of England for instance has been gradually rising since the retreat of the glaciers and was approaching its future equilibrium in a cyclical manner with a periodicity of centuries. 
Mörner wryly noted that the new IPCC ‘trend’ line showed a general sea level rise averaging 2.3 mm…exactly the same amount as the only one of six Hong Kong tide gauges to show a 2.3 mm rise. His own findings which showed no rise were derived from field studies carried out in many parts of the world, based on measuring direct physical evidence such as tides, shore lines and marine deposits.
The Danish academic Bjorn Lomborg's best guess...and his guesses are better than most because he knows what he is talking about...is that sea levels will rise over the coming century about a foot or about as much as they rose over the past 150 years.
To learn more read Cool It!: The Skeptical Environmentalist's Guide to Global Warming...the antidote to what Lomborg refers to as 'choreographed screaming'. This detailed study of global warming is published by Marshall Cavendish. (London, 2007, 352 pps, £19.99, ISBN 978-0-462-09912-5) and includes a thousand references and a thousand endnotes.
If sea levels rise this amount it will be a problem...but it won't be a catastrophe. Ask a very old person about the most important issues that took place in the 20th century. She will likely mention the two world wars, the cold war, the internal combustion engine and perhaps the IT revolution. But it is very unlikely she will add: 'Oh, and sea levels rose.'
'We dealt with sea levels rising in the past century, and we will do so in this century too. It doesn't mean that it will be unproblematic, but it is unhelpful...and incorrect...to posit it as the end of civilization.
Moreover sea level rise will be a much bigger problem for countries that are poor than for countries that are wealthier. In fact if we work hard at reducing sea level rises, it is likely that we will reduce the rise by 35% but at the same time end up making each person about 35% poorer. The upshot is that places such as Micronesia and Tavalu will get three times more flooded, simply because lower incomes more than outweigh the lower sea level rise.
Thus we cannot just talk about CO2 when we talk about dealing with climate change...we need to bring it into the dialogue considerations both about carbon emissions and about economics, for the benefit of both humans and the environment.
 Globally one of the core concepts in the measurement of sea levels is the geoid…the equipotential surface of the earth’s gravitational field that approximates the mean sea surface. But there are plenty of other complications. There are the complexities of glacio-hydro-isosatic modelling and the eustatic and tectonic effects on shoreline dynamics. And even with some rudimentary grasp of these subjects there is still holocene sedimentary sequences and intertidal foraminifera distributions to master. And when that is done waiting in the wings are the carbon analysis of coastal paleoenvironments and aminostratigraphy. Sea level is not simple...and is complexity squared when wrestling with time series stretching back over centuries and millenia.
 In South East England for instance the land is oscillating up and down on its way to finding a new level after the melting of the ice at the end of the last ice age. In an area like Romney Marsh this means dramatically different shorelines since Shakespeare's time when the English fleet would take refuge between the Cinque Ports of Rye and Winchelsea.