PERU'S forests cover 72m hectares of the country (278,000 square miles). That is three times the area of Britain. And Peru intends to hold on to its greenery. In 2000 its deforestation rate was 250,000 hectares a year. By 2005 that figure was down to 150,000. This year, according to Antonio Brack Egg, the country's environment minister, it will be 90,000. In 2021, if all goes well, it will be zero.

To make sure things stay on course, Dr Brack says, the government needs to spend more than $100m a year on high-resolution satellite pictures of its billions of trees. But he hopes that a computing facility developed by the Planetary Skin Institute (PSI), a not-for-profit organisation set up by Cisco Systems, a large computing firm, and America's space agency, NASA, might help cut that budget.

The PSI's Automated Land-change Evaluation, Reporting and Tracking System, ALERTS, is one of several tools being developed to assess the extent and health of forests and other ecosystems. These tools should make the implementation of a deal on reducing deforestation called REDD+, agreed on at the United Nations' climate-change conference in Cancún on December 11th (see article), easier to monitor. The PSI's intention is to apply the world's ever-increasing supply of information to the problem of its ever-dwindling natural resources by merging data of different types. ALERTS, which was launched at Cancún, uses data from NASA's MODIS cameras (of which two are currently in orbit) data-mining algorithms developed at the University of Minnesota and a lot of computing power from Cisco's “cloud” of machines to spot places where land use has changed.

Juan Carlos Castilla-Rubio, a Cisco executive who is also president of the PSI (and, as it happens, is from Peru), says that ALERTS has been tested against the Brazilian space agency's PRODES system, which is a respected way of measuring deforestation using satellite images. The areas singled out by ALERTS as undergoing change closely matched those that PRODES's researchers had assessed as being deforested. ALERTS, unlike PRODES, has a global reach. And its algorithms automatically reassess every spot on the planet every six weeks, cloud (of the meteorological sort) permitting. PRODES cannot manage that. Dr Brack's ministry is now working with the PSI to get a sense of how it can use ALERTS to distinguish those bits of forest it needs to look at in more detail from those that are doing fine as is.

Redd Alerts

Mr Castilla-Rubio sees ALERTS, and the PSI's other projects, as “global public goods”—resources that everyone with an interest can share. The same phrase is used by Alessandro Baccini, part of a team at the Woods Hole Research Centre, in Massachusetts, who used the opportunity provided by Cancún to talk about a new analysis of how much the world's tropical forests actually weigh—and thus how much carbon they are storing.

To calculate this, the team took data from patches of forest studied on the ground, in which every tree's diameter has been recorded, and combined them with images from MODIS and with data from an instrument called GLAS, which bounced laser beams off the Earth's surface between 2003 and 2009. GLAS's main job was measuring the height of ice sheets, but the data that came back from forested areas contain a lot of information about the height of the canopy and the density of the vegetation there. That allowed the team to turn the two-dimensional images from MODIS into three-dimensional models. From these it is possible to estimate the mass of plant matter (and thus the quantity of carbon stored) in an area.

Dr Baccini's group is not the only one to have used GLAS data in this way. Sassan Saatchi, who works at NASA's Jet Propulsion Laboratory in Pasadena, California, and his collaborators have combined such data with the results of other studies on the ground and with a wider range of satellite images. Neither team has yet published its results: one set is about to be submitted to a journal, the other is in review.

What is already known, though, is that for various parts of the world the results do not match. Bad news for short-term applications; good news as a way of focusing in on what needs to be improved. Simon Lewis, a forest ecologist from Leeds University who was in Cancún as part of the delegation from Gabon, a heavily forested country keen on being paid to stay that way, is looking forward to comparing the new models with his own data as soon as they are published. Seeing what is happening on the ground in the mismatched places could lead to more reliable estimates in future, and possibly to some interesting science as well.

Those future estimates will not be able to use new GLAS data. The instrument has died, as orbiting lasers are wont to. But for local and regional estimates lasers can be flown on aircraft. That gives results which are a lot more reliable than the first stabs at doing the whole world from orbit. A recent study of 4.3m hectares of Peru, carried out this way by Greg Asner of the Carnegie Institution, in America, and his colleagues, produced precise estimates of forest loss, forest degradation (thinning out of the trees) and reforestation, while also yielding insights into the way that geographical features and types of soil influence the amount of carbon stored in different places. Dr Asner is now working on a national survey of Colombia.

He has also created software that will help analyse deforestation using a huge archive of satellite images that Google is making available. Google's new “Earth Engine” will offer these data free, along with analytical tools like Dr Asner's and yet more cloud-computing power to help people use them. This may prove complementary to the PSI platform, in that the Earth Engine helps you study a given place, whereas ALERTS helps you choose which places to study. (Another freebie for researchers in Gabon, and the rest of central Africa, is the provision of satellite data for forest work by Astrium, a European aerospace company, in collaboration with the French government.)

These new ways of bringing data together have a lot of promise. Dr Baccini says he is keen to know what the PSI's data-melding power might do with his work. Add a few new instruments in orbit, and the practical and fiduciary interest in the matter spurred by anti-deforestation deals like REDD+, and you can expect far better estimates than are now available of how much carbon is really locked up in forests and other habitats. Not only will they be better, but the way they are arrived at will also be clear and their results comparable and checkable. That will leave less room for obfuscation, or even fraud.

Moreover, as ever-better ways of measuring local carbon-dioxide levels become available, it will be possible to put figures on not just the amount of the gas that deforestation is releasing, but also how much of it photosynthesis is tucking away. The science will move from static estimates of stocks to a sense of the system's dynamic flows. As Peter Drucker, the management guru's management guru, once put it, what gets measured gets managed. If that maxim holds in ecology as well as in business, the future of the world's forests is bright.