This opinion is in contrast to recent publications by the Intergovernmental Panel on Climate Change (IPCC), which projects rises of less than a metre. In a paper in Environmental Research Letters, Hansen criticizes the IPCC predictions and what he calls "scientific reticence" in the field of research into sea level rises. The IPCC's 2007 figures are lower that its 2001 predictions and this, says Hansen, has sent the wrong message to the public giving an impression that scientists are now less concerned about sea level rises.

"Field glaciologists have been doing a good job of reporting current trends on the ice sheets," says Hansen. "It is translation of field data into conclusions needed by the public and policymakers that is at issue."

Hansen is concerned, for example, that the summer melt on West Antarctica has received less attention than the summer melt on Greenland. "This is probably simply because Greenland is closer to us," he says. "But what is happening in West Antarctica is more important."

In his Environmental Research Letters paper Hansen claims that the IPCC 2007 figures are low because the IPCC says it is unable to evaluate possible dynamical responses of the ice sheets and therefore its figures do not include any possible rapid dynamical changes in ice flow. "This gives an inaccurate and incomplete picture and sends the wrong message to the public and to policymakers," says Hansen.

He told environmentalresearchweb that he believes there is a huge gap between what is understood about human-made global warming and its consequences, and what is known by the people who most need to know - the public and policymakers. "This is due in part to scientific reticence," says Hansen. "Reticence in science is often appropriate in areas where scientists have time to reflect on their work before making a statement or expressing an opinion, but we simply do not have that time."

He is concerned that the scientific community discourages scientists from expressing strong opinions that are different to the consensus. "I believe there is a pressure on scientists to be conservative. Papers are accepted for publication more readily if they do not push too far and are larded with caveats. Caveats are essential to science, being born in scepticism, which is essential to the process of investigation and verification. But there is a question of degree," says Hansen.

He admits reticence is appropriately recognised as an asset that makes IPCC conclusions authoritative and widely accepted. It is probably a necessary characteristic given that the IPCC document is produced as a consensus among most nations in the world and represents the views of thousands of scientists.

"IPCC is doing a commendable job, but we need something more," says Hansen. "Given the reticence that IPCC necessarily exhibits, there need to be supplementary mechanisms. The onus, it seems to me, falls on us scientists as a community."

Hansen argues in his paper for "calling together a panel of scientific leaders to hear evidence and issue a prompt plain-written report on current understanding of the sea level change issue".