I wonder if this is due to clearing and growth of grasses or some other succession.

http://www.geotimes.org/july03/NN_green.html

In the June 6 Science, Running and colleagues analyzed historical productivity data from a past generation satellite, AVHRR, covering from 1982 to 1999. “When you combine the Science paper with the two years of MODIS data, we see that the NPP of the terrestrial biosphere has increased over these 20 years. The world really has gotten more productive in plant growth, and the Amazon has had the highest increase in productivity rate,” he says.

They found that since 1982 the NPP is up 6 percent globally and is up 20 percent in the Amazon, which stands out on the new 2002 NPP map. Their historical data suggests that the productivity in the Amazon is accelerating faster than in areas of the northern high latitudes, such as Alaska and Canada, previously thought to be the fastest growing terrestrial carbon sinks. The leading cause of the global productivity increase, the Science authors suggest, is climate change with some contribution from carbon dioxide fertilization and forest regrowth.

~samwik

I recall an earlier thread (page 11) about a drier Amazon "growing" more. As the grasses replace the forest, they'll increase NPP (grassland NPP > jungle NPP) as well as dry out the area (also increasing NPP).

Sounds good, but a drier Amazon won't be good in the long run.

What strikes me is that even with the terrestrial NPP increasing (~1/2 GtC/yr), CO2 levels aren't falling.

I think it's because Marine NPP has fallen so much.
Not to say we shouldn't try to increase terrestrial NPP also (bogs and golf courses).

But for food and fuel we already appropriate 40% of terrestrial NPP. I think we should look to the marine NPP to increase our food and fuel resources.

~SA