The unprecedented rate of destruction of Brazil's rainforest over the last three years came into public attention during Brazilian President Luiz Inácio Lula da Silva's three-day state visit to Britain.
The criticism came as the UK and Brazil signed an agreement Tuesday to work together to combat climate change. The two countries agreed to cooperate on global promotion of low carbon technology, climate change science and related issues.
Since he came to power three years ago, President Lula failed to stop 70,000km? of rainforest being cleared - an area equivalent to that of the Republic of Ireland - says Greenpeace.
"The only reason Brazil is in the top five polluters is the destruction of the rainforest," John Sauven of Greenpeace told Radio 4's Today programme Wednesday.
Although 65% of Brazil's electricity comes from hydroelectric dams, the positive impact on carbon emissions is more than offset by deforestation due to illegal logging, cattle ranching and large-scale soya cultivation, says Greenpeace.
On Tuesday, President Lula da Silva wrote about the environmental progress he has made while in office in a Guardian newspaper article:
"The scale of Brazil's natural assets is extraordinary: the Amazon region contains 20% of the planet's fresh water, and almost two-thirds of the country is still covered by natural vegetation."
"When I began my term of office, the rate of deforestation in Brazil had been increasing by an average of 27% per year. From the second half of 2004 onwards, however, we put measures in place to monitor tree-felling and to address the issue of land distribution, with the result that the rate of deforestation has fallen dramatically."
Nevertheless, Brazil's forests are still being cleared at a faster rate than in any other country, said Greenpeace's John Sauven.
He acknowledged the steps president Lula has taken to halt rainforest destruction, reducing the rate of loss of forest area by 30% in 2004-2005.
The Greenpeace comments and the new UK-Brazil agreement to establish a "high-level dialogue on climate change" come in the lead-up to the UN Convention on Biological Diversity meeting, to be hosted by Brazil on 20 March.
The agreement "demonstrates our commitment to tackling the challenges of climate change as well as progressing discussions under the UNFCCC on a long-term climate change agreement," said UK Environment Secretary Margaret Beckett when signing the statement together with Brazil's Foreign Minister Celso Amorim.