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Greg Asner on carbon in the Amazon rainforest

From above, the treetops in the Amazon rainforest might look remarkably uniform. But different regions of the rainforest might store very different amounts of carbon.

If you were to gaze at the Amazon rainforest from above, much of its 1.4 billion acres would look remarkably similar. But ecologist Greg Asner of the Carnegie Institution reported in September of 2010 that different regions of the rainforest might store very different amounts of carbon. Carbon storage helps cool Earth, scientists believe, by keeping C02, a greenhouse gas, out of the atmosphere.

Greg Asner: It’s really all about how much carbon is in the living wood in each of these trees.

Asner surveyed the Amazon rainforest of southern Peru – an area about the size of Switzerland – to figure out the exact amount of carbon locked up in its trees. Asner used lasers from above and also ground observations to create a 3-D map. He discovered this particular area of the Amazon stored 395 million metric tonnes of carbon. That’s a lot – but about 20-25% less carbon than scientists previously estimated.

Greg Asner: The reasons for that we’re still exploring. One of the things that came as a surprise to me is that the geology has a very strong effect in the patterns we see.

In other words, rocks and soil appear to – somehow – affect the level of carbon storage in the Amazon’s trees. Since there’s a lot of variety in the Amazon’s rocks and soil, Asner said, huge patches of rainforest could potentially store even more carbon than scientists now know. Or less. Either way, scientists can better pinpoint where.

Greg Asner: We’ve developed, for the first time, a way to measure the carbon landscape of a very large area. And that’s what a lot of our work is about, trying to facilitate the maintenance of carbon in these forests, rather than having it emitted through deforestation, degradation.

Asner clarified that just because the Peruvian Amazon might have less carbon than scientists previously estimated, that doesn’t mean that the Amazon is any less important to global climate.

Greg Asner: When we found in this study less storage, we’re talking about a lesser amount on a very big number. No matter how you cut it, there’s a lot of carbon in these tropical forests.

Dr. Asner explained that the primary ways carbon is released into the air in the Amazon is when a rainforest is degraded in some way, whether through farming, logging, burning, or road-building.

Greg Asner: The clearing of the forest for activities like cattle ranching, crop agriculture and biofuels or degradaction – that’s selective logging and burning. That carbon goes into the atmosphere as CO2 or carbon dioxide, and that is a very potent greenhouse gas that contributes to global warming.

He spoke about the far-reaching importance of rainforests, in general:

Greg Asner: If you were to take all of the carbon that’s stored in all tropical forests – the Amazon is about half of the total – but if you were to take the global amount and burn it all up you would emit into the atmosphere about five times the carbon dioxide than is already in the atmosphere. So that’s a huge amount of carbon sitting in these trees that, in terms of climate change, we don’t want released into the atmosphere.

Asner reported his findings in September 2010 in the Proceedings of the National Academy of Sciences.

Beth Lebwohl