Polar bears have bad breath – really bad – imagine eating nothing but raw seal blubber all your life and never brushing your teeth and you'll get the idea. I know this because I had my face six inches from the, fortunately anaesthetised, jaws of an adult female bear in the company of David Attenborough and the Norwegian scientist Jon Aars on the high Arctic island of Spitzbergen in April 2010.

We were there to film for the final episode of Frozen Planetin which David travels to both Arctic and Antarctic to observe the effects of climate change and investigate what they might mean for the rest of the planet.

The Norwegian Polar Institute has been monitoring the polar bears of Svalbard since the 1970's. This work, combined with similar such long-running studies in Alaska, Canada and Greenland, has helped to reveal the link between years of poor ice cover on the sea and poor cub survival in subsequent years. That's because polar bears need ice to hunt seals, and cubs born to mother bears that are underweight from a poor hunting season are weaker.

All across both polar regions the scientists were able to point to a long record to support their assertions of dramatic change. The meteorologists talked of a 3C temperature rise on the Antarctic peninsula over the past 50 years – a rate matched in parts of the Arctic, but nowhere else on Earth. The satellite scientists showed us the images from the late 1970s and early 80s, which showed the 30% drop in sea ice cover which leads most experts to suspect that the Arctic will be ice-free in the summer sometime between now and 2050.

And everywhere we went we found the scientists not just keen to tell us about their work, but actually able to show us the changes they had been measuring. The most dramatic example of this was the break-up of the Wilkins ice shelf on the Antarctic peninsula. This huge floating mass of fresh water ice, the size of Yorkshire and 200-metres thick, started to break apart in 2008, just as production on this film began.

Such are the difficulties and expenses of polar logistics that it was not until February 2010 that we were in a position to attempt to film this globally significant event. By this stage, bizarre though it seems, even the satellite experts could not tell us what there would actually be to see if we managed to reach the location. That season's satellite images were affected by cloud and showed a confused jumble of grey that was difficult to interpret – would there simply be a mass of slush where the Wilkins had once been? That would be intellectually interesting but not the dramatic image we had our fingers crossed for.

None the less, we took the gamble. The British Antarctic Survey pulled out all the stops to try to get us into place – transporting us to Rothera, the nearest base to the ice shelf, putting us up and even giving us first refusal on the use of one of their precious Twin Otter planes. But they could not control the Antarctic weather and clouds and snow kept us trapped in the base for a week before the skies finally cleared and we were able to make the flight.

To say we were not disappointed would be a breath-taking understatement. What greeted us was the most extraordinary sight I believe I will ever see. The break-up had continued and the Wilkins was now in a state of full collapse – hundreds upon hundreds of icebergs – many over a mile long, were stretching to the horizon.

It was an incredibly beautiful scene but I was left with the same uneasy feeling I had when stroking the polar bear. On a personal level this film has given me the experiences of a lifetime but the reality of some of the beautiful things I've seen is, if you'll pardon the pun, chilling.

• Dan Rees is the producer of the On Thin Ice episode of the BBC's Frozen Planet series, which airs on Wednesday night at 9pm on BBC One