The NewYork Times has highlighted a major milestone: atmospheric CO2 reaching 400ppm as ridiculed in this post and this one.
Despite all the doom and gloom (some people want to drive CO2 levels back to 350ppm) but CO2 is plant food and good for human populations. See this post on the impact on agricultural productivity at higher CO2 levels. From Nature (2011)
key point from the abstract: As predicted, elevated CO2favoured C3 grasses and enhanced stand productivity, whereas warming favoured C4 grasses. Combined warming and CO2 enrichment stimulated above-ground growth of C4 grasses in 2 of 3 years when soil moisture most limited plant productivity. The results indicate that in a warmer, CO2-enriched world, both SWC and productivity in semi-arid grasslands may be higher than previously expected.
In looking further, this idea was already well documented . Here is a review article from 1999. Response of ...grass..to elevated ... CO2.
What can we do with higher productivity of C3 and C4 plants? Feed more people.
What level of CO2 is optimum? Some greenhouse operators increase yields by raising levels to more than 1000 ppm.
A comparison of plants grown at different levels of CO2 shows that 350ppm is nearly starvation levels compared to the lush growth at higher levels. The industrial revolution may have come just in time to prevent world wide crop and population failures due to CO2 loss.
Here is a video link that illustrates the effect.