This is a question of of tone and confidence. Which report provides a more stark view of the dangers of climate change? (I'm comparing the summaries since that's the only part the vast majority of people will read, and therefore is a good view on what the IPCC Working Group II wanted to emphasize.) On current effects of climate change: 2007 : With regard to changes in snow, ice and frozen ground (including permafrost), there is high confidence that natural systems are affected... Based on growing evidence, there is high confidence that the following effects on hydrological systems are occurring: increased runoff and earlier spring peak discharge in many glacier- and snow-fed rivers [1.3]; warming of lakes and rivers in many regions, with effects on thermal structure and water quality There is very high confidence, based on more evidence from a wider range of species, that recent warming is strongly affecting terrestrial biological systems... Based on sa