Human activity is pushing the environment past danger points that could signal danger for life around the planet, according to a new report.

In March 2010, a group of 30 scientists from around the globe developed a list of nine environmental processes vital to the long-term survivability of the human race. These included acceptable levels of stratospheric ozone, ocean acidity, and atmospheric aerosol concentrations. When the report was released nearly five years ago, the panel declared that humans had already "crossed the line" in three categories - upsetting the nitrogen cycle, diversity loss, and climate change. Now, scientists are warning the world may have passed a fourth mark in the degradation of the environment - destruction of forests.

Woodlands around the world are bulldozed, cut, or burned down, in order to provide land for agriculture, industry, and habitation. Forests consume vast quantities of atmospheric carbon, which can offset some of the effects of greenhouse gases released by humans. Water vapor, essential for the growth of woodlands, is also reduced when forests are cut back. Loss of this vegetation can not only contribute directly to global climate change, but altering terrain can change the amount of light reflected by the ground back into space, potentially altering climate.

"Transgressing a boundary increases the risk that human activities could inadvertently drive the Earth System into a much less hospitable state, damaging efforts to reduce poverty and leading to a deterioration of human wellbeing in many parts of the world, including wealthy countries. In this new analysis we have improved our quantification of where these risks lie,"  Will Steffen of the Stockholm Resilience Centre at Stockholm University and the Australian National University, said.

The new report was released by 18 international researchers, some of whom helped to develop the original analysis. The team believes the original nine boundaries were too many for public leaders to effectively address. Their new reassessment names two core boundaries, which investigators believe could drive the planet to a new, undesirable, state.

Biosphere integrity - a measure of biodiversity and the state of natural habitats around the globe, was one of the factors researchers are highlighting. A loss of such integrity could adversely alter growth of plants and animals on which humans depend on survival.

Climate change was declared to be the second core boundary, primarily measured as the concentration of carbon dioxide in the atmosphere.   

Researchers hope the new analysis will help guide the United Nations in the development of new environmental goals for nations and organizations.

Planetary boundaries: Guiding human development on a changing planet, detailing the loss of forests and what that could mean for human survival, was published in the journal Science.

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