Activist and former Brazilian presidential candidate Marina Silva called Tuesday for protests matching the magnitude of Egypt's Tahrir Square demonstrations at an upcoming UN environmental meeting.

More than 100 heads of state and tens of thousands of participants from governments, the private sector and NGOs will converge on Brazil later this month for the Rio+20 United Nations Conference on Sustainable Development.

Marking the 20th anniversary of the "Earth Summit" in 1992 in Rio de Janeiro, the gathering aims to break years of deadlock on pressing environmental issues and set up long-term paths towards green development.

"I hope that Rio+20 will become the Tahrir Square of the global environmental crisis and that international public opinion will be able to tell leaders that they cannot brush off the science," Silva told AFP, referring to skepticism about climate change and alluding to the Cairo square that became the epicenter of the uprising that ousted Egypt's Hosni Mubarak.

"They cannot lower expectations in the face of a crisis worsening every day," said Silva, the 53-year-old figurehead of Brazil's environmental movement.

The Brazilian military plans to deploy 15,000 security personnel for the UN summit and a parallel "people's summit" at the Flamengo park in southern Rio, which will be sponsored by civil society and is expected to see the attendance of nearly 20,000 people a day.

Silva urged the government to rethink a new forestry code recently approved by Brazil's parliament, warning that it would increase the deforestation of the Amazon and prevent the country from meeting targets on reducing CO2 emissions.

"This sends a bad signal on the eve of the Rio+20 when Brazil could have been an example," Silva said.

"If on the eve of the Rio+20 we practically eliminate the law that protects forests, we change the law that defines the boundaries of indigenous lands and we withdraw the capacity of a federal agency responsible for combating illicit deforestation... imagine what will happen," she said.