Small average global temperature change can have a big impact

Climate scientists admit that the chances of the world keeping average global temperature at current levels are not going to be possible (humanity has done little to address things in the past couple of decades that these concerns have been known about).
So, now, there is hope that temperature rises can be minimized to an average 2°C increase (as an average, this means some regions may get higher temperatures and others, lower).
Even just a 2°C increase can have impacts around the world to biodiversity, agriculture, the oceans etc (detailed further below). But in the lead up to important global climate talks at the end of 2009, some delegates are skeptical that temperature rises can be contained to a 2°C rise (or C0 2 levels of 350 ppm ).