You might like to support SOS Mata Atlantica, who have a carbon neutralization program in addition to other conservation programs focusing on the highly threatened Atlantic forests.
http://www.sosmatatlantica.org.br/
http://www.florestasdofuturo.org.br/paginas/home.php
Projects include reforestation of hydrological basins and watersheds.
They may not have anything on the site in English, but it couldn't hurt to send an email or letter to their contact addresses.
Beyond carbon impacts, if interested in something more bird-oriented, try a donation to BirdLife Brasil (SAVE Brasil). They have never had a specific website, but you can find contact details through the BirdLife website or simply make a donation requesting funds specifically support the Brazilian programs. The birds and habitats can certain use some help!
cheers
Brad