We've known for a couple of years or so that one of the impressive-sounding environmental promises that governments are signed up to - the pledge to reduce the rate of biodiversity loss significantly by 2010 - isn't going to be met.

Now, an analysis just published in the journal Science is giving us detail on some important dimensions of the problem.

It's particularly timely, as we are now on the path towards October's UN biodiversity convention summit in Nagoya, Japan. There you can expect all of these bones to be picked over, and some new targets to be set.

If you've been following the issue, the basic pattern should be familiar.

Numbers of species, size of populations, diversity within ecosystems: all these are going down.

Habitat loss, the spread of harmful alien species, depletion of fish stocks: all these are going up.

Joining the dots and concluding that the second batch of things causes the first isn't a leap of deduction likely gain you a Nobel Prize.

The Science paper, compiled by an impressive array of scientists across disciplines led by Stuart Butchart from the UN's World Conservation Monitoring Centre and BirdLife International, does three things that may prove useful.

• It sorts out what we know and what we don't know, and in which regions

• It refines measurements of how the various threats are changing

• It puts all of this together in a global whole

As usual, the global picture that scientists would like to have is in reality a patchwork of local and regional pixels, with the added constraint that the time-line for measurements in many parts of the world starts only a few decades ago.

If the availability of good data on something as simple as temperature is patchy across the world, imagine how much patchier it is when it comes to issues such as the rate of nitrogen deposition or the changing abundance of birds.

Where things can be assessed from published data - for example, the size of protected areas declared by governments - you can obviously get a more precise figure than where you have to go out and do field measurements in 270 patches of forest with four day of hiking between them.

So, for example, the researchers concluded that the spread of invasive alien species can only really be assessed in Europe at this stage.

Some fisheries records are only usable from 1997. Just 16 countries submitted data on the extent of seagrass in their waters.

So you get the picture - a fragmented one, at best.

Nevertheless, some trends are clearly discernible, both downwards and upwards.

Picking out some examples, Dr Butchart tells the BBC's Science in Action programme:

"In my lifetime, the condition of coral reefs has declined by 40%, animal populations have declined by a third, and we've lost 20% of the extent of mangroves and seagrasses."

Arguably, the drivers of biodiversity loss are more important than the biodiversity trends themselves.

After all, society is not deliberately trying to send species extinct - it's trying to clothe itself and feed itself and get itself around faster and so on - and as long as society continues trying to do these things faster and faster using the same technologies and materials, you'd logically expect biodiversity loss to keep on going.

Of these drivers, the spread of alien species, the impacts of climatic change, loss of habitat and the over-exploitation of fish stocks are all trending inexorably upwards - the only exception is nitrogen deposition, which appeared to reach a plateau around 1990, although some would argue it's on the way up again now.



Despite the limitations of the data available, governments are undoubtedly better informed about biodiversity decline and its causes than at any time in the past.

There's no room left to claim "we don't understand the problem".

But the problem is closely tied to human development - the rising population, the rising use of resources, eating more food, building more roads, using more energy.

Halting these implies a cost: which is why there's growing interest now in documenting the costs of not halting them - of totting up the value that intact ecosystems bring, and what it would cost to replace the services they provide.

There'll be more on this along during the year. But Dr Butchart has another, much simpler point:

"All nature has intrinsic value. What right have we got to drive hundreds of thousands of species extinct and deny our children, grandchildren or future generations the opportunity to benefit from and appreciate the species around us?"

Whether we have the right or not, it's exactly what we are doing, as this Science paper shows us in greater detail than ever before.

