How much of the Netherlands is below sea level?

a) 60 percent

b) 55 percent

c) about half

d) 26 percent

It sounds like a trivia quiz but it’s part of a scientific controversy about the environment. The worrying thing is that a lot of people who should know don’t.

If you reckon it’s 60 percent, you can point to a report by the Dutch Ministry of Transport, Public Works and Water Management, or an article in the journal Nature discussing the Netherlands’ vulnerability to flooding after Hurricane Katrina.

If you think it’s 55 percent, then you can back up your argument with page 547 of an influential 2007 report by the U.N.’s Intergovernmental Panel on Climate Change (IPCC).

And if you reckon that it’s about half, try showing off the European Commission’s report listing “facts and figures” about the Netherlands and its maritime policies.

But the Netherlands Environmental Assessment Agency , the source of the IPCC’s number, says all the above are in fact wrong — it’s 26 percent, and another 29 percent of the country is vulnerable to flooding from rivers such as the Meuse and the Waal in regions above sea level.

In this Dutch version of Chinese whispers, the problem seems to be that 26 plus 29 equals 55 which might also be ‘about half’ or ‘60 percent’.

The IPCC, under fire for exaggerating the melt of Himalayan glaciers in its 2007 report that wrongly said that they might all be gone by 2035, said that it probably made a mistake by saying 55 percent. It said that its report should probably have read that 55 percent of the Netherlands is “at risk of flooding”.

But just as worrying is that the Dutch government, the EU Commission and scientists writing in a top journal apparently get it wrong too.

Somewhere along the line this sort of number is used to decide how much money to spend on coastal or flood defences. If you reckon that 60 percent of your country is below sea level, building coastal levees probably gets a bigger share of the cash than defences against river flooding than if the right number is 26 percent.

(Picture: An excavator moves sand at the new beaches in front of the Dutch coastal village of Monster August 31, 2009. REUTERS/Jerry Lampen)