We've had a fair bit of chat here in recent months about diversity in the natural world, and why it matters - with some regular posters asking whether in fact it matters at all.

I've tried to lay out some of the evidence - there is quite a lot - showing that diverse ecosystems tend to be more robust and also inherently more productive, which leads to real human benefits when we're talking about an ecosystem that provides something we need, such as food.

This week the journal Nature places another brick in the wall.

Ray Hilborn and colleagues from the University of Washington (the one in Seattle) looked at records from one of the most valuable fish in US waters - the sockeye salmon, sales of which fetched the somewhat mind-boggling sum of $8bn over the last half a century.

(That's just the value of the landed fish - when you take into account other aspects such as tourism revenues associated with recreational fishing, the true value to the US economy is presumably higher.)

Sockeye salmon are especially plentiful in the waters around Bristol Bay on the western coast of Alaska - a large expanse of sea into which nine major rivers empty their waters - and their salmon.

Each of those rivers is fed by tributaries, and some feature topographically tortured sequences of lakes along their length.

What this translates into is a subtly diverse range of habitats for the sockeye salmon. And with their famous homing instincts, the fish have thus segregated themselves into over 100 more or less discrete populations (presumably there is a bit of interbreeding between them) that lead subtly different lives, including coming downstream at different times.

The researchers asked a simple question. Supposing you didn't have all this diversity - suppose you just had one batch of homogenous salmon - what then?

Now, any perturbation (a rough winter affecting something that fish eat, for example, or a big storm on a certain day) is going to affect the entire batch pretty much across their range.

The homogenous population would see much more see-sawing in output, culminating in a ten-fold increase in the number of fisheries closures, the university team concluded.

Because all the salmon would "run" at the same time, the fishing fleet would have to be bigger in order to catch the same total number of fish - a less economic endeavour.

Among the non-economic impacts the team enumerates, salmon diversity improves prospects for predators such as bears, which can get around from stream-to-stream taking advantage of the seasonally-varying abundances.

Would you invest all your money in a single stock (assuming you dabble in such things at all)?

The wise answer would probably be no, and certainly not over an extended period. Unsurprisingly, the extra robustness of the output from the diverse salmon stock is termed here the "portfolio effect".

However, the other conclusion from the paper is that reducing nature's portfolio is exactly what has been going on further south along the Pacific coast.

More populated as these regions are, more altered by the needs of cities and industry and agriculture, nearly a third of the pre-industrial-era 1,400 Pacific salmon populations have been wiped out since the arrival of European settlers.

It doesn't translate into a species extinction or even close, so it raises but small signals in the conservation community; but on the fishing industry, it's probably had a big effect already, simply through reducing the portfolio.

Bristol Bay is not immune from the spread of development and the growing need for resources.

Whether or not there should be oil drilling there has been a live issue for years, and there are proposals on the drawing board for a big multi-mineral mine - Pebble Mine - which opponents fear could pollute local waters, to the detriment of the fish and all that stems from the fish.

Quantifying the economic benefits of the sockeye salmon's ecological portfolio won't guarantee the mine won't be built or that the area won't see vast oil and gas extraction in the coming years - nor should it, you might say, because the world needs oil and gas and copper and molybdenum, just as it needs fish.

But it should make for more rational decision-making, enabling local people and the authorities to factor in more accurately the costs of development as well as the benefits.

And on the broader stage, it provides one more argument for ecological diversity - and why the current loss of it is concerning many policymakers, even as they struggle to find ways of containing that loss.

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A group of experts convened under a UN umbrella has been taking a look at what aspects of our global society are the least sustainable; which things are depleting natural resources fastest, which are causing the most environmental damage, and which are the biggest threats to the prosperity of future generations.

It's bad news, I'm afraid, because the biggest culprits are the things we need most fundamentally: food and energy.

We're used to emissions from fossil fuels being fingered as the principal drivers of the man-made greenhouse effect.

But the report from the UN Environment Programme's International Panel for Sustainable Resource Management also points up the immediate polluting effects (and health consequences) of burning coal, wood, oil and gas.

Meanwhile, other types of emission also compromise human health and the natural world, such as nitrogen run-off from agricultural land, which causes eutrophication in freshwater systems and the seas.

On the resource side, the report flags up the coming declines in oil and gas reserves as stumbling blocks on the developing world's path to prosperity. But shortages of key ingredients for alternative technologies - such as platinum and rhodium - are also causes for concern, it says.

When it comes to the Earth's self-replenishing resources, wood and fish are the ones we are using least sustainably.

Farming, meanwhile, is fingered as the principal reason why natural habitat is being lost for so many plants and animals, with high consumption of meat - relatively heavy on land and water use - flagged up as a particularly unsustainable aspect of western diets.

More than half of the crops we grow are used to feed farm animals.

Much of this, you may be thinking, is not terribly radical; it's the usual depressing story of people trying to live ordinary lives, and copping the blame when what they need to live and progress starts running out or overloading nature's waste-processing capacity.

What I think is interesting is the way the global picture is re-framed.

So rather than talking about "stopping climate change" or "reducing the health impacts of wood-burning" or whatever, the panel makes two principal offers.

Firstly, it's using real, quantified studies to pin down as far as is possible the real costs and benefits of many of the things we do; and it's doing so in a holistic way.

Secondly, it's offering choices rather than a prescription: rather than the language of "we have to stop doing this", it's a matter of "if society develops this way, these are likely to be the consequences for your children's generation; and here's how it changes if you develop that way instead".

In some ears, this will be ringing an alarm bell that resonates to the tune of "here's another UN anti-growth message".

It actually isn't; it's about rationalising growth. As the panel summarises its remit:

"All economic activity takes place in a limited, natural world...so what economic activities contribute most to the use of natural resources and the generation of pollution?"

And having produced answers, choices and some solutions then emerge.

As one of the panel's co-chairs, the eminent German scientist Ernst Ulrich von Weizsaecker, told me:

"One strategy is to decouple wellbeing from resource consumption. Another is to select resources in relation to their environmental impact, and so it's important to know where the big impacts are."

This report doesn't offer an easy path to curbing the expansion of our global footprint; it doesn't come close, in fact.

But it does suggest a way in which the overarching issue encompassing the world's environmental, economic and social ills might be addressed, and development maintained, without costing the Earth.

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The international development charity Oxfam has a new report out asking some fundamental questions about climate finance.

If you recall, two different financial pledges emerged at the Copenhagen summit: "fast-start" money to the tune of $30bn over the three-year period 2010-2012, and the much larger amount of about $100bn per year by 2020.

Both sums are supposed to be raised in and by industrialised nations, and made available to their poorer counterparts - to help curtail their greenhouse gas emissions, and to help them adapt to impacts of climate change.

Estimates of the true costs of these changes in the developing world vary significantly, and it's worth recalling that neither figure emerged from genuine negotiations - both were floated well ahead of time by western leaders, and changed not a jot as Copenhagen proceeded - so whether the sums are enough is one of the issues that Oxfam doesn't want us to lose sight of.

The other issues that it flags up are ones that in principle should be easier to answer, but which right now are about as murky as the Gulf of Mexico.

Is the money new, or are western countries seeking to redirect existing aid budgets? Will any of it be offered as loans? How much will come from the public purse?

Underlying these is the most fundamental of all: will it actually materialise?

These questions are not easy to answer, largely because there is no single conduit for funds.

Donor governments insist that bilateral transfers of money can count towards the total; and as these contributions can be wrapped up as components of bigger projects (for example, as additional funds to flood-proof a school being built with aid money), there is obviously a lot of potential for figures to jump magically from one column of the ledger to another.

At the April session of the UN climate convention (UNFCCC) in Bonn, EU representatives announced that by June they would have a report on the table summarising and clarifying contributions from EU member states.

It's not happened, and the idea now is to bring it out by the end of the year. So we will be one-third of the way through the "fast-start" period before we discover whether the EU is actually making good on its part of the $30bn pledge, and whether any uncomfortable questions hang over the raising and disbursement of the funds.

Given their domestic political difficulties, clarity from the other two major promisers of money - Japan and the US - is in even shorter supply.

Oxfam flags up a couple of other specifics. Some governments, it relates, are keen that money transferred through the UN's Clean Development Mechanism (CDM) should count towards the bigger long-term target of $100bn per year.

CDM money is spent on reducing greenhouse gas emissions, certainly. But the reductions accrue to the western countries that are paying for the reductions - so allowing this as a contribution to meeting the Copenhagen pledges would be a clear case of double counting.

Secondly, some governments are apparently arguing that some of the $100bn should be proffered as loans, not as a transfer of funds.

As Oxfam points out:

"Climate finance is not aid. It is not an act of charity, or an expression of solidarity with poor countries, but a legal obligation under the UNFCCC."

The outcome of last week's Climate and Forest Conference in Oslo both illustrated how some governments are attempting to move forward, and highlighted some of the obstacles that encumber the process.

The Norwegian and Indonesian governments agreed a deal that on the surface at least enshrines accountability on both sides.

Indonesia agrees to halt deforestation for two years: Norway agrees to hand over $1bn if it does so, and will demand evidence before it parts with the cash. As part of the mechanism, Indonesian President Susilo Bambang Yudhoyono says he will "personally monitor" the forestry sector.

So far, so clear.

The conference also trumpeted the news that western countries had upped the sum they were pledging to combat deforestation in 2010-12, from the $3.5bn announced in Copenhagen to $4bn.

What we don't know is whether the extra half billion is additional money, or whether it comes from the overall $30bn pot.

Given the overall lack of transparency that Oxfam and others are flagging up, my bet is that no-one could tell us.

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