If there's one part of the world that could be considered the canary in the coal-mine of climate change, it's the frozen ice sheets of the Arctic. That's where temperatures are rising fastest, and where the effects, in a visibly shrinking ice-cap, are most dramatic. And the apparent flooring of Arctic sea-ice levels this decade, has just been reinforced by news from the NSIDC - this March's ice area is tied for the lowest March maximum on record, last set in 2006.

The tracking of sea-ice changes over time is a tricky business, because of the natural see-sawing, with the seasons. In winter the ice area tops 15 million square km, whereas in winter it plunges to less than 5 million sq km. So scientists monitoring the levels compare the yearly peaks and troughs, to get an idea of the longer term trend in sea-ice levels.

The National Snow and Ice Data Center (NSIDC) is one a several groups monitoring sea-ice levels, using microwave sensors on polar satellites. March is the time when the sea-ice flips from its winter growth to a summer slide-down; and this maximum is looked out for, keenly, each year. The NSIDC has just 'called' the maximum for the 2010-11 winter, based on the last 5 days showing falling sea-ice levels; the provisional numbers come out at 14.64 million square km

This is a whopping 1.3 million sq km below the average March maximum seen from 1979-2000, and ties the lowest previous maximum, seen in 2006. This only confirms the strong downward trend in the Arctic ice-sheet, when looked at over a number of years. Tracking the differences from the average, for each year, shows an accelerating rate of ice-loss growth, especially in summer. Some scientists project an ice-free Arctic within our lifetimes - and possibly even within a decade or so.

Not only does the shrinking polar ice-cap demonstrate the very real effect of global warming, right here and right now - the consequences may be colossal, if this continued ice-loss takes us towards open water at the north pole. There could be massive unforeseen changes in everything from oceanic current flows, to regional climate, and it may even cause the release of climate-shaking levels of methane.

Some consequences may already be showing themselves in the snow-chaos of the last 3 winters. Climate scientists have noticed that these exceptionally cold and snowy winters, for North America and Europe, appear related to the weakening of the 'polar vortex'. Those spinning winds usually keep Arctic air locked up around the poles. Sea ice melting could be undermining that cold air 'fence'. So it seems that the canary is tweeting louder and louder. The question is - is anyone listening?