By TOM WRIGHT

Kees Visser’s In Response of Oct. 28 on the topic of global warming was welcome. The more we discuss climate change the closer we may come to understanding it. We’ve got to get it right. Misinformation is positively dangerous. Visser’s’ admonition to “stick to the facts” is a wise one.

Alarm bells went of for me, though, to see “mere” computer modelling referred to as armchair fiction which is consistently proven wrong. Computer modelling is a widely used self-correcting scientific tool. By continually testing hypotheses, then rigorously correcting parameters, computer modelling becomes increasingly accurate over time.

Before satellite imagery, small changes in sea level were hard to measure. Shorelines continue to adjust to post-ice age melting, some rising, some falling. Tectonic movements also change land levels, sometimes gradually, sometimes suddenly. We know that sea level was 130 metres lower 20,000 years ago, but centuries of later sea level observations were compromised by our inability to separate sea level changes from land level changes.

This probably explains why I was quite unable to confirm Prof. Nils-Axel Moerner’s four “facts” in the scientific literature. Current thinking is that sea level has risen an average of two mm/year for the last century, increasing to three mm/year for the past decade, and still increasing. Sea level rises partly due to thermal expansion and partly due to melting of land ice.

Kees is quite correct to say that neither melting Arctic sea ice nor floating Antarctic shelf ice will directly affect sea level. It is not correct to say that melting glacier ice (i.e. moving land ice) will have a negligible effect on sea level, however. It is a major contributor.

It is also wishful thinking to expect increased snowfall to negate the effects of melting ice across Antarctica. For millennia, extremely low temperatures have made Antarctica a near desert. Increased snowfall will result from warming, and thicker snow packs drive the flow of glaciers to the sea.

The three largest icecaps on Earth are on Greenland, West Antarctica and East Antarctica. Our understanding of how they melt has increased tremendously in the last couple of years. Melt water has been observed flowing deep into crevasses (moulins) on icecap surfaces, particularly on Greenland and West Antarctica, as well as on glaciers worldwide. Melting and sliding then occur at the base of the ice. Spectacular increases in outward flow rates of glaciers and also “ice rivers” within the icecaps are evident. You have only to turn on your television to see massive blocks of land ice tumbling into the ocean. This is real sea level rise.

The huge East Antarctic icecap was long believed to be thick enough to insulate deep ice layers from rapid melting. Another shock! We now know that the thick ice blanket traps geothermal heat from below. Recent seismic exploration has located large melt water lakes beneath the ice, and areas of surface slumping in the order of tens of metres suggest substantial movements of deep water.

The potential for much-accelerated collapse of the icecaps should not be ignored. The three icecaps alone contain enough ice to raise worldwide sea level by over 70 metres should they melt completely.

Since observable atmospheric CO2 continues to increase, and faster than expected melting permafrost and mountain glaciers are widely evident, it seems logical to predict faster melting of the icecaps. We do not know how fast this melting will occur, or how fast sea levels will rise as a result. Educated estimates range between one metre and three metres this century. Either would be disastrous in low-lying countries of the world.

A disruption in the climate pattern should be anticipated when the dark Arctic Ocean waters become exposed to the long summer days when the reflective ice cover melts over the next few years. Releases of methane and CO2 will intensify the warming as permafrost melts and ocean temperature rises.

We certainly should not be so complacent as to think we can carry on as normal. If “keeping a cool head” means ignoring the evidence all around us, we are in for some rude shocks.

Incidentally, the actual wording of the 4th Assessment Report of the IPCC in 2007 (mentioned byVisser in his article) was:

Warming of the climate system is unequivocal and most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

“Anthropogenic” means “caused by humans.” That’s us, folks!

The writer is a geologist and environmentalist who co-wrote the climate change piece Kees Visser responded to in last week’s Driftwood.