The Monday Reuters agency report in the Herald on changing sea levels in the Pacific island group of Tuvalu, "Sinking Culture Snapped", is misleading.

Since instrumentation was installed in 1993 on Tuvalu's main island Funafuti, sea level has shown no discernible trend. There is some inundation evident on islands in Tuvalu, but global warming is not the cause.

It is the result of erosion, sand mining and construction projects causing an inflow of sea water.

Other factors are also involved.

Excessive use of freshwater for irrigation also causes destruction of underground freshwater reservoirs. A consequence is seawater encroachment into vegetable growing pits is occurring, but is not due to sea level rise.

Part of the problem is related also to the paving of the roads and the runway on Funafuti.

According to estimates, about one quarter of the island has been paved over.

The effect of this has been to reduce infiltration of rainwater into the freshwater lens. When this increased runoff is combined with a high tide, flooding along the coast looks like the sea level is rising.

Perception of trends can also be affected, as increasing population on the islands means people are now living on flood prone land that was previously avoided.

Coral is capable of growing faster than most if not all past rates of sea level rise. The atolls are not static.

The islands grow as they are replenished by coral that breaks off the reefs and is thrown ashore by storms.

In that way atolls are self-maintaining, provided humans don't intervene, such as by digging the coral for use in construction work, and building flush toilets that discharge the effluent into the sea and where it affects coral growth.

Reasonable scenarios of sea level change are based on calculations that rely on scientifically sound assumptions. Over the short term, climate warming could cause sea level to rise mainly by the thermal expansion of the oceans.

Melting of polar ice caps is not involved since this is a long-term response. As only the surface water is affected, response times can be rapid, but sea level rises of only a few millimetres are possible even for the worst cases of warming.