Two campaigns to recalibrate and communicate our expections of how much CO2 in the atmosphere is appropriate to the earth's wellbeing. 350 parts per million (ppm) is one message, the other is 300 ppm.
In 2008, we'd reached 387 ppm. Article here.
Both are considered 'aggressive' by the recommendations we've been used to from reports such as Garnaut (450-550). The higher targets are usually set by those who believe that climate action (reductions of GHG emissions and of atmospheric levels of GHGs) can only take place within a 'business as usual' (and/or a 'politics as usual') scenario. In other words, we can only reduce GHGs if it does not significantly impact on our current lifestyles/profits.
Unfortunately, the science of global warming indicates that these targets are not low enough. The climate does not care about maintaining our lifestyles and will respond to the laws of chemistry and physics and not the laws of economics.
As we are often reminded, a satisfactory response to climate change requires that we address the science. No amount of discussion about the rights and wrongs will fix the problem, only a reduction of GHG emissions will do that.
A snappy (90 second) animation: