‘You don’t have to be an astronomer, it’s enough to think logically. The earth circles the sun in an elliptical-shaped orbit, and so during its revolution sometimes it’s closer and sometimes further away. The further the earth is from the sun, the colder it is on it; that must be logical. And the less the world’s axis deviates from the perpendicular the less light reaches the northern hemisphere.’

‘That’s also logical.’

‘Both those factors, I mean the ellipticalness of the orbit and the degree of tilt of the world’s axis, are subject to changes. As can be observed, cyclical ones. The ellipse may be more or less elliptical, that is stretched out and elongated, and the earth’s axis may be less or more tilted. Extreme conditions, as far as climate is concerned, are caused by a simultaneous occurrence of the two phenomena: the maximum elongation of the ellipse and only an insignificant deviation of the axis from the vertical. The earth orbiting the sun receives very little light and heat at the aphelium, and the polar regions are additionally harmed by the disadvantageous angle of tilt of the axis.’

‘Naturally.’

‘Less light in the northern hemisphere means the snow lies longer. White and shining snow reflects sunlight, the temperature falls even more. The snow lies even longer because of that, it doesn’t melt at all in greater and greater stretches or only melts for a short time. The more snow and the longer it lies, the greater the white and shining reflective surface…’

‘I understand.’

‘The snow’s falling, it’s falling and falling and there’s more and more of it. So observe that masses of warm air drift with the sea currents from the south, which condense over the frozen northern land. The warm air condenses and falls as snow. The greater the temperature differences, the heavier the falls. The heavier the falls, the more white snow that doesn’t melt for a long time. And the colder it is. The greater the temperature difference and the more abundant the condensation of the masses of air…’

‘I understand.’

‘The snow cover becomes heavy enough to become compacted ice. A glacier. On which, as we now know, snow continues to fall, pressing it down even more. The glacier grows, it’s not only thicker and thicker, but it spreads outwards, covering greater and greater expanses. White expanses…’

‘Reflecting the sun’s rays,’ Condwiramurs nodded. ‘Becoming colder, colder and even colder. The White Frost prophesied by Ithlinne. But is a cataclysm possible? Is there really a danger that the ice that has lain in the north forever will all of a sudden flow south, crushing, compressing and covering everything? How fast does the ice cap spread at the pole? A few inches annually?’

‘As you surely know,’ said Nimue, eyes fixed on the lake, ‘the only port in the Gulf of Praxeda that doesn’t freeze is Pont Vanis.’