By Marcelo Teixeira

SAO PAULO (Reuters) - A new online monitoring system will make it possible to quickly check the condition of tropical forests around the globe that were previously under no surveillance, potentially increasing pressure on governments to stop deforestation.

Washington-based World Resources Institute (WRI) will provide public access on Thursday to the new tool to evaluate forests worldwide. Global Forest Watch (GFW) was developed by dozens of institutions with the help of Google Inc's Earth Engine.

It promises to improve scrutiny of changes in forest cover in vulnerable areas of Southeast Asia, Africa and the Amazon.

"For the first time, we have united in one place powerful satellite information analyzed in a way that is easy to understand," said Nigel Sizer, director of WRI's Global Forest Initiative.

The system uses high resolution data from half a billion Landsat satellite images to measure tree cover loss or gain. It also carries a tree cover loss alert, pinpointing where new forest clearing occurs.

"With the exception of Brazil, none of the tropical forest countries have been able to report the state of their forests," said Rebecca Moore, engineering manager with Google Earth Outreach and Earth Engine. "Now it will be possible to have near real-time updates of the state of the world's forests, open to anyone to use."

The project was made possible by the Landsat imagery archives opened to the public in 2008 by the U.S. Geological Service, Moore said.

WRI expects the new system to also increase the pressure on commodities suppliers in countries where forests are at risk.

Swiss food giant Nestle said the new tool could contribute to better oversight of suppliers of raw materials such as meat, soy and palm oil.

"It is going to help us dramatically to refine our work on the ground, in places where we think there might be issues with our supply chain," said Duncan Pollard, associate vice president for sustainability at Nestle, a program collaborator.

Global Forest Watch will embed key information in the images. For example, it will be possible to check which palm oil company is operating in a specific area of Indonesia where images have shown recent forest destruction. That could lead to a buyer canceling purchases from a supplier, WRI's Sizer said.

Carlos Souza, from Brazilian forest research center Imazon, a partner in the program, said projects to reduce emissions from deforestation and forest degradation could receive a boost due to increased data transparency.

"Investors could feel more comfortable to take part in projects if they can track forest loss," Souza said.

The governments of Norway, the United Kingdom and the United States are among the largest donors for the initial investment of $25 million to build the tool.

(Editing by Nick Zieminski)