I've reported before that global warming may be worse than is currently thought. And I've further made the point that forecasts and predictions depend on linearity, and that reality is likely nonlinear, and therefore forecasts are likely to be conservative.
This point has just been reinforced by a study on sea levels. As described at ThinkProgress and the NY Times, the study shows that earlier measurements of sea level were too high, the implications of which are that sea levels have in recent years risen more than was earlier thought. This goes to the point that I made about nonlinearity in forecasts, the changes we are undergoing are accelerating, faster than a linear project would conclude. In other words, sea levels are going to rise to greater levels at a sooner time than we thought.