09.39am: Hello, and welcome to our rolling coverage of Rio+20, where world leaders have flown in overnight to attempt an agreement to make the global economy more sustainable for people and the environment.

Formally called the UN Conference on Sustainable Development, it is the largest UN summit ever organised, and comes 20 twenty years after the original Rio Earth summit and 40 years after a similar meeting in Stockholm. On the table are three main themes: better governance, plans to grow the 'green economy' of industries such as renewable energy, and progress on agreeing 'sustainable development goals'. Read our Latin American correspondent Jonathan Watts' excellent Q&A for more on the background.

François Hollande (France), Vladimir Putin (Russia), Mariano Rajoy (Spain), Julia Gillard (Australia) and Manmohan Singh (India) are among the big name leaders attending. Barack Obama is not, though there are rumours in the Brazilian press that he will make a last-minute appearance.

Other no-shows include Angela Merkel of Germany, and David Cameron, who is reportedly not going because he will be at the G20 meeting in Mexico just before Rio+20 and "could not be out of the country" for that long. The UK is represented by environment secretary, Caroline Spelman, and deputy prime minister, Nick Clegg, who's written in the Guardian today on Rio and announced mandatory carbon reporting for FTSE100 firms.

The leaders that are there will be playing a game of expectation management. Clegg is already at it in his article:

I don't expect this week's meeting will be as show-stopping as that in 1992, but it matters just as much.

The official 'high level segment', which starts today and ends Friday, comes against the backdrop of widespread anger and disappointment from politicians and campaigners at the draft agreement text adopted yesterday. Here's some of the initial reaction on Twitter, from EU climate commissioner Connie Hedegaard, Denmark's environment minister Ida Auken (Denmark currently holds the EU presidency), Jim Leape, the head of WWF International, and Kumi Naidoo, Greenpeace International's executive director:

#rioplus20 telling that nobody in that room adopting the text was happy. That's how weak it is. And they all knew. Disappointing #Rio20

Nick Clegg. Photograph: Carl Court/AFP/Getty Images

— Connie Hedegaard (@CHedegaardEU) June 19, 2012

Not the best agreement in the world, but an agreement for a better world #RioPlus20

— Ida Auken (@IdaAuken) June 19, 2012

Brazil has released new text. If this becomes final text, the past year of negotiations has been a colossal waste of time. #RioPlus20 @WWF

— Jim Leape (@jimleape) June 19, 2012

This is Rio Minus 20 which Fails on equity, fails on ecology,Fails on economy #rio+20 #earthsummit text longest suicide note in history

— Kumi Naidoo (@kuminaidoo) June 19, 2012

10.15am: Spelman, who was leading the UK's delegation at the talks yesterday, is upbeat about the text:

Caroline Spelman. Photograph: Dan Kitwood/Getty Images

Whilst there is still a lot of work to do, this agreement means we have made progress towards achieving what the Rio Earth Summit set out to do – to get the world on the right path to achieve cleaner and greener growth that ends the damage we have done to the environment and helps end poverty. The agreement on Sustainable Development Goals is a good outcome.

Though she admits it's not all rosy:

Clearly not everything we hoped for has been agreed and there is more to do to turn the words into actions. But the future we want was never going to be achieved in one week. We have to go one step at a time, and this has been a big step forward.

10.25am: And while most of the other reaction to the text has been gloomy, there are more exceptions.

Selwyn Hart, diplomat for Barbados, told Reuters:

The document represents a positive step forward. While it is not the major breakthrough we had 20 years ago it puts us on the pathway to sustainable development. The formal negotiations might be over but (leaders here tomorrow) need to focus on the implementation of some of the central issues dealt with in the document.

Clegg also told the Today Programme that, while the UN process may not be perfect, the multilateral approach it embodies was vital:

"Frustrating & slow moving as these summits may be... there is no escape we have to deal with these issues globally." - @nick_clegg #Rio+20

— BBC Radio 4 Today (@BBCr4today) June 20, 2012

10.39am: What's not clear yet, is whether the agreement reached yesterday – which you can read in full here, if you've got the stomach for it – will be reopened in the next three days. As our correspondent on the ground, Jonathan Watts, writes here:

Brazilian President Dilma Rousseff at Rio+20. Photograph: Buda Mendes/Getty Images

President Dilma Rousseff is now thought unlikely to reopen debate, which means the event is likely to end not with a bang, but a whimper of photo-opportunities, handshakes and speeches.

But while it seems that the negotiations may have finished before most of the heads of state even arrived, it is technically possible that discussions on the document will be reopened, if the Brazilian hosts allow it.

As Gro Harlem Bruntland, who effectively defined the concept of 'sustainable development' in the run-up to the 1992 Rio Earth Summit, told the Guardian:

Maybe because there is so much pessimism at the moment, the outcome may be better than people fear. There are more than 100 leaders coming after all. They are not going to leave with nothing.

10.49am: Geoffrey Lean, one of the UK's longest-serving environment journalists, has some interesting insight on the Telegraph's site into how the negotiations between officials have panned out over the last few days:

Any hope that today's summit would do much about any of this [the world's environmental problems] died long ago. Indeed, it did not even set out to produce any new binding agreements: its ambition only extending to producing an exhortatory, aspirational document. But preparing even this proved impossible, as negotiators spent weeks haggling over even the most anodyne wording.

Finally, on Saturday, the Brazilian chairmen of the preparatory meeting lost patience, produced their own version of the document and have since been ramming it through, line by line, in order to have something for the leaders when they arrive. They have refused to accept any suggestions, unless unanimously agreed, and even told one Swiss delegate who begged for time off at the weekend "to see your beautiful city" that his only opportunity would be to go jogging before breakfast. The price, however, was to produce a text even weaker than what was already on the table.

The verbs tell the story. The word "encourage" appears 50 times, the phrase "we will" only five; "support" is used 99 times, "must" just three.

And this too, on the hosts:

...the Brazilians have shown little interest in the summit. President Dilma Rousseff has been distinctly unenthusiastic and her respected environment minister, Izabella Teixeria, has been sidelined as her government has played up divisions between developed and developing countries to cover its lack of seriousness.

10.55am: Bit of a mixup. The Greenpeace banner hanging off Christ the Redeemer happened in 2006. So I've removed the reference and tweet to it here.

11.28am: Jonathan Watts, who is about to head out to the Riocentro Convention Centre where the summit is being held, tells me the negotiating stage of Rio+20 is effectively over:

The Guardian's Latin America correspondent, Jonathan Watts. Photograph: Ben Mcmillan for the Guardian

They [the Brazilian hosts] seem to have been trying to avoid what happened at Copenhagen [where UN climate talks ran past the final day into the early hours]. The text is agreed. Now the world leaders who are arriving will play a largely ceremonial role. Europe has indicated it's not likely to push for the negotiations on the text to be reopened, and I'd say it was 90% likely they won't be reopened. It's a very Chinese way of doing things [like the annual Lianghui, or 'two meetings'] where most of what's under discussion is prearranged, and leaders only make small tweaks. The idea is for it to all be very harmonious.

Today, we're likely to get speeches from countries on how the agreement will be implemented. But the negotiating stage seems to be over – it looks like we've moved into the photo opportunity stage.

11.43am: This is interesting, on the subject of leader no-shows. Damian Carrington, the Guardian's head of environment, notes that a new ComRes poll of UK MPs shows that almost 60% think that Prime Minister David Cameron should have attended the Rio+20 summit:

Damian Carrington

Despite the summit being moved to avoid the Queen's Jubilee, Cameron decided not to go, sending Nick Clegg instead. The poll, conducted for the Planet Earth Institute, surveyed 110 MPs and the results were weighted to be representative of the whole house. As for the government's pledge to be the "greenest ever", even the coalition's MPs are unconvinced, with only 52% of Conservatives and 61% of Liberal Democrat MPs believing the government is fulfilling this pledge.

As Watts pointed out to me, Clegg and Hilary Clinton don't have the arm-twisting power of Cameron and Obama at these sort of meetings.

11.58am: On the subject of no-shows, where is Boris Johnson when you need him? The London mayor, who made a showy appearance at the Copenhagen climate change conference in 2009, was conspicuously absent from a side-event C40 meeting of mayors from 58 megacities around the world.

Here's New York's mayor, Michael Bloomberg, who spoke to the BBC from the event in Rio de Janeiro:

Michael Bloomberg. Photograph: Spencer Platt/Getty Images

New York City has reduced its carbon emissions in the past two years by 13%... it is cities that are making differences. Cities and mayors don't have the luxury of just talking about it... In cities mayors are held accountable for cleaning the air, cleaning the water.

The Mayor's office told me they suspect decisions had been taken regarding Johnson's diary in the run-up to the Olympics. But it "doesn't follow that the Mayor not being there detracts from our commitment to climate change", a spokeswoman said. It's a similar line to what Spelman told MPs when defending Cameron not going: "there is no suggestion with the prime minister not going that the UK is not taking Rio seriously"

12.14pm: There's a good post from David Nussbaum, head of WWF UK, on how we ended up with the text agreed yesterday:

What they did [the Brazilian government in the past few days] was take all the 'bracketed' issues out of the text altogether. Text gets bracketed when it's controversial – and here in Rio, it's proved to be controversial when it's been ambitious and looking to change the status quo.

And so the controversies have been addressed through compromise and capitulation in varying measures. The result is a weak text, lacking in much ambition in terms of clear actions and dates, and it doesn't measure up to the vision we have of a safe world for both people and nature.

Brazil did not accept any more new text unless it mustered consensus from all countries (which is as likely to happen as a sloth winning the 100 metres in the Olympics).

The G77 of 132 developing countries including China were "pretty happy with the text" since "they don't want environmental protection to mean any impact on their prospects for economic growth." The result, he says is that:

it's left to the EU, joined by countries like Switzerland, Norway and Japan to push for more stringent targets and the stronger environmental regulation that requires. But the G77 have pushed back, and the EU backed down. The US doesn't want anything that suggests they will have to commit more financing, especially for the UN.

And so the negotiations became polarised. The result is a race to the bottom, where weaker levels of ambition are political wins, and the loser is the lack of progress towards a safe and equitable world, to say nothing of the natural resource and systems that we all depend on.

12.48pm: Time for a spot of inspiration, to recognise some of the voices of civil society in town for Rio+20. Here's Brittany Trilford, a 17 year-old from New Zealand at Rio as a 'voice of youth' – this generation's Severn Suzuki, if you like – who won a competition to attend the summit (full disclosure: I was one of the judges). This is her talking at Rio on Monday – she's also due to address the opening plenary session today.

And here's an excerpt if you don't have time for the full video:

My name is Brittany Trilford, I am 17 years old and I'm here to fight for my future. That's it. I'm here to fight for my future. Because I have to fight for it...

I may be young and not educated in the ways of commerce, but I still take maths in school, and even I can recognise things are not adding up. We plunder away our natural resources, diminishing our biodiversity, our oceans, our forests... We have used the planet like we own it. But even when I own something, I look after it. We are taught these things in school. Things just don't make sense...

They made great promises [at Rio 92]. These promises are left not broken, but empty. They remain, but are unsupported.

...I would like to now ask you here today: why are you here? Are you here to take strides for the common good, or succumb to corporate greed? I hope you are here ready to commit and work hard for a future we can look forward to. Are you here to hedge your bets, and save face? Or are you here to save us?

12.29pm: The deputy prime minister has landed:

Just arrived in Rio for the #RioPlus20 Summit. I've written for the @Guardian today outlining what I hope to achieve - bit.ly/KSV1bD

— Nick Clegg (@nick_clegg) June 20, 2012

But with the negotiating stage seemingly over (see 11.28am update below), what can Clegg achieve beyond what's already been agreed? Watch this space.

1.26pm: I just had an interesting chat with a spokesman for the UK delegation, which is currently driving to the Riocentro Convention Centre. He effectively confirmed Watts' analysis of the situation: that the negotiating stage of Rio+20 is over, and the text that's been agreed is what we'll get.

Well obviously they [heads of state] still have to agree it. It is still a draft. All countries have agreed to it, but it has to be put to the heads of state in the next few days. There will be a lot of discussion as to how we take this forward, and turn this into action - the implementation.

[But] We don't expect the text to get reopened, or to get significant changes... There will be very little, if any, change.

He said Spelman and Clegg will spend the next three days on a "lot of bilaterals, talking to world leaders, attending some of the many events." Clegg is now head of the UK delegation.

Finally, a quick heads-up: the opening plenary of the summit is scheduled for 2pm UK time today, which will include remarks from UN secretary general, Ban Ki-Moon.

1.42pm: My colleagues on Comment is Free are running a Rio-themed poll: "Would you eat less meat to help save the planet?" Currently the ayes have it, with around three quarters of the vote. You can add your voice on the poll here.

They've also got a comment piece up from the Brazilian foreign minister, Antonio Patriota, hailing the summit as a "historic moment". He doesn't get into the nitty gritty of the text that's been adopted, but writes:

Brazil's Minister of the Environment Isabella Teixeira (L) speaks next to Brazil's Foreign Minister Antonio Patriota on Tuesday. Photograph: Andre Durao/AFP/Getty Images

From now on, a three-dimensional approach to development is crucial, one that combines social, economic and environmental concerns. Rio+20 is endeavouring to become the launch pad for this new development model. This is why one of the main topics of Rio+20 is building consensus around the need for "sustainable development goals". They will offer a blueprint for international co-operation on sustainable development for years to come. Future strategies, be it for governments, entrepreneurs or civil society, must offer a balanced and integrated approach encompassing the three pillars of sustainable development.

1.57pm: Liz Ford, the deputy editor of the Guardian's Global development website, writes in from Rio about the hellish-sounding traffic congestion:

You can tell the important people are in town today as traffic in Rio is at a standstill on the way into the conference centre. Fortunately our driver has managed to work his charm with the guy in a uniform trying to insist we join the very long queue of traffic to our right. Our press passes and pleading smiles may also have helped. We are now stuck in another traffic line but it's a VIP one just for those attending Rio+. Who knows, Nick Clegg could be in the car in front...

Seems like she's not the only one. The US EPA administrator, Lisa Jackson, missed the C40 mayor event yesterday (see 11.58am update) because she was stuck in traffic, AP reports:

...the significant challenges still facing this seaside metropolis of 9 million were underscored by the absence at Tuesday's conference of the U.S. Environmental Protection Administrator Lisa Jackson, who missed the conference because she was stuck in Rio's notorious gridlock.

Speaking of important people, the celebrities have begun to arrive. Here's actor Ed Norton:

In Rio for start of #Rioplus20 and discussions of #futurewewant. Official start today. Follow @UN_Rioplus20 

— Edward Norton (@EdwardNorton) June 20, 2012

Looks he might be disappointed, though, on the amount of discussion going on. As has fast become apparent this morning, its seems the negotiations for an agreement at Rio+20 are largely over.

2.24pm: While we're waiting for the opening plenary and Ban Ki-Moon, which has been delayed 'til 3pm BST, here's this from Damian Carrington. He notes that not everyone is unhappy with the lack of progress in Rio. Bjorn Lomborg, author of the Sceptical Environmentalist, had this to say today:

Danish professor Bjorn Lomborg. Photograph: Adrian Dennis/AFP/Getty Images

A breakdown at Rio+20 might be a good thing. The UN has chosen to focus on trendy issues like global warming and a green economy instead of banal - but much more important environmental issues - like air and water pollution. For every one person that dies from global warming, about 210 die from air and water pollution. In other words, twenty years from now, we could have saved 120 million lives, if only Rio+20 had focused on solving simple environmental problems. Instead, we're spending money on windmills, solar panels, biofuels and other rich world obsessions.

2.44pm: In a Rio-timed flourish, the UK's announced £20m of the international aid budget will be spent over four years for forests in Liberia, Ghana, Rwanda, Brazil, Mexico, El Salvador and Indonesia. It's for a "forest management 'knowledge bank' to help indigenous people in the poorest and most remote forest areas to protect their incomes and escape the impact of deforestation."

Here's how international development secretary, Andrew Mitchell, explains it:

Andrew Mitchell, the international development secretary. Photograph: Oli Scarff/Getty Images

Bringing together the knowledge of local communities, private investors and international partners will have a direct impact on tens of millions of people who rely on forests to survive. But we will all benefit from this investment in sustainable forest management. By minimising deforestation we will all profit from cleaner air and directly ease the devastating levels of chronic poverty suffered by so many.

It's not additional to the government's existing aid budget, a Dfid spokeswoman tells me – but it is a welcome allocation of cash on an environmental project.

3.00pm: The opening plenary, with Brazilian president Dilma Rousseff, foreign minister Antonio Patriota and UN secretary-general Ban Ki-moon, is being streamed here.

Lot of admin taking place at the moment.

3.07pm: Here's what Trilford from New Zealand (see 12.48pm update) had to say to the opening session, including over 100 heads of state:

I stand here with fire in my heart. I'm confused and angry at the state of the world and I want us to work together now to change this. We are here to solve the problems that we have caused as a collective, to ensure that we have a future.

You and your governments have promised to reduce poverty and sustain our environment. You have already promised to combat climate change, ensure clean water and food security. Multi-national corporations have already pledged to respect the environment, green their production, compensate for their pollution. These promises have been made and yet, still, our future is in danger.

...We, the next generation, demand change. We demand action so that we have a future and have it guaranteed. We trust that you will, in the next 72 hours, put our interests ahead of all other interests and boldly do the right thing. Please, lead. I want leaders who lead.

I am here to fight for my future. That is why I'm here. I would like to end by asking you to consider why you're here and what you can do. Are you here to save face? Or are you here to save us?

3.20pm: Some more comment on the text adopted at Rio Rio+20's secretary-general and Chinese diplomat Sha Zukang, who said:

I am especially pleased to join the host government of Brazil in announcing that the negotiations have come to a successful conclusion. We now have a text, which will be submitted for formal adoption. We think the text contains a lot of action/ And, if this action is implemented, with follow-up measures taken, it will indeed make a tremendous difference in generating positive global change. Like all negotiations, there will be some countries that feel the text could be more ambitious. Or, others who feel their own proposals could be better reflected. But, let's be clear: multilateral negotiations require give and take

And Patriota:

We are giving indications to the future, a new vision for the future. This is a common vision for the future, a vision for sustainable development. It was a puzzle that was not easy to complete. For me it was a great personal satisfaction to see how constructive the process was and how all parties showed a wish to take the collective responsibility for the text.

3.23pm: The text agreed by officials yesterday is getting a slating from groups at the opening session in Rio.

Here's the UN women's major group:

It is a shame there is such a timid text here at Rio. No commitment to our reproductive rights. No high commissioner for our girls. Nothing about the destruction by nuclear power and mining... The Rio outcome document does not give us the urgently-needed means to address the massive challenges of our times.

And the UN major group for children and youth:

This is not the future we want... Children and youth feel grossly frustrated by this outcome document.

3.36pm: Wow. We knew NGOs were unhappy with the Rio+20 text, but they have held no punches in their criticism of it to an audience of world leaders.

Here's the UN major group of NGOs at the opening session:

We stand on the brink of Rio+20 being another failed attempt. With governments only trying to protect their narrow interests instead of trying to inspire the world. If that happens, it will be a big failure.

...You cannot have a document called the Future We Want without any mention of planetary boundaries, tipping points or planetary carrying capacity.

...The text as it stands is completely out of touch with reality. Just to be clear, NGOs at Rio do not endorse this document.

They cited a few examples of what the considered failures in the text:
• no mention of the end of fossil fuel subsidies
• failed to give clear mandate to even make a start on end to abuse of high seas
• missed opportunities to start new treaties on sustainable reporting
• extraodinary lack of any reference to nuclear power, espeically in light of Fukushima disaster

They also called for the removal of the phrase "full participation of civil society" in the opening paragraph of the text agreed on Tuesday, if it goes ahead in its current form:

with full participation of civil society, renew our commitment to sustainable development, and to ensure the promotion of economically, socially and environmentally sustainable future for our planet and for present and future
generations.

4.06pm: Ban Ki-moon was, unsurprisingly, a lot more upbeat at the opening session about the agreement reached, compared to civil society:

Ban ki-Moon said organisers had purposely scheduled Rio+20 immediately after the G20 meeting in Cabo San Lucas, Mexico, hoping to lure Obama and other world leaders to attend. Photograph: Shawn Thew/EPA

We are now in sight of a historic agreement. Let us not waste this opportunity. The world is watching to see if words will translate into action, as we know they must.

I am pleased that negotiations have reached a successful conclusion and I commend the Presidency of Brazil for facilitating this resolution.

We have been given a second chance [after the original Rio Earth summit in 1992]

Rio+20 is not an end but a beginning. It is time for all of us to think globally and locally.

Here's what the UN cites as some of the text's achievements:
• beginning the process to establish sustainable development goals
• detailing how the green economy can be used as a tool to achieve sustainable development
• strengthening the UN Environment Programme (UNEP)
• promoting corporate sustainability reporting measures
• taking steps to go beyond gross domestic product to assess the well-being of a country

3.54pm: Greg Jones, a science journalism postgraduate who's on a placement at the environment desk here, has been speaking to our correspondent Jonathan Watts about the state of play at Rio. "Something will come out of this. It's unlikely to please everybody here, and it's certainly upset lots of people in environmental NGOs, but things could have been a lot worse," says Watts. You can listen to the full interview here:

Watts cites the announcement of a $175bn sustainable transport fund as one of the concrete positives to come out of the summit.

4.57pm: Watts has just been at a press conference with the UN secretary-general, who's made a nod to the campaigners and countries not happy with the agreement:

Some member states hoped for a bolder ambitious document. I also hoped that we could have a more ambitious outcome document. But you should also understand that negotiations have been very difficult and very slow because of all these conflciting interests.

We'll have a full news story shortly.

5.01pm: Robert Mugabe has been speaking for about 15 minutes at Rio+20. Greg Jones here has been taking down what the president of Zimbabwe said.

Robert Mugabe. Photograph: Sipa Press/Rex Features

He began by discussing the history of Zimbabwe's contribution to previous meetings but admitted failings in the country's commitments to environmental pledges.

Mugabe cited a "failure of the three pillars of sustainability: economic, social and environmental dimensions."

"To date, our record of meeting pledges has not been something to be proud of.
When there are challenges in the global economy, investment in the future is always the first casualty."

He highlighted the inequalities between nations, saying that developed nations must "shoulder responsibility" for their actions.

He also said, "there should be no room for elitist clubs in the field of sustainable development. We are all in peril, and we should act in concert for the common good."

However, he also commented that, "the green economy is not synonymous with abandoning the use of natural resources that we have in abundance, such as coal."

(he said these things were important in zimbabwe's development and in tackling poverty, hunger and growth)

He closed by expressing his hope that Rio+20 would not "go down in history as one of those gatherings that promised a lot but delivered little".

Some people tweeting from the meeting made clear they were unimpressed that he was clapped at the end of his speech:

Why on earth did anyone applaud Mugabe's speech? Apart from it's nice now that he's stopped talking. #rioplus20

— Chris Lang (@reddmonitor) June 20, 2012

People here have just CLAPPED Mugabe. THAT IS HOW BAD THE SITUATION IS HERE. SEND HELP. #Rioplus20

— Hanna Thomas (@hannathomas) June 20, 2012

5.14pm: Here's the official line on Boris Johnson not being at Rio (see the 11.58am update), from a spokeswoman for the mayor:

Boris Johnson. Photograph: Luke Macgregor/Reuters

London is a committed and leading member of the C40 with the Mayor being represented at the Rio+C40 Megacity Mayors event by his environment advisor, Matthew Pencharz. Matthew is participating in a range of events designed to promote the vital role that London and large cities are playing in addressing climate change, outlining the opportunities and challenges they face.

5.29pm: There's a briefing on natural capital – i.e. putting a financial price on nature in a bid to theoretically better conserve it – taking place in Rio+20 now, which Clegg is speaking at. Here's the Guardian's Liz Ford on a little stunt by the campaigners at the World Development Movement

The WDM has had its eBay 'nature sale' cancelled. It seems you can't sell off the Lake District or the Sumatran tiger, although that's what WDM is saying governments are trying to do at Rio through its Ebay stunt. This afternoon the UK is hosting a high level dialogue on 'natural capital' which effectively puts a price on nature. Kirsty Wright, from WDM, calls this "ridiculous". "By selling off iconic natural sites such as the Amazon rainforest and Lake District we are simply following the UK's approach that the intrinsic value of ecosystems can now be qualified and that they can be owned, speculated on and ultimately sold off to whoever has the most money."

I've just tweeted it so you see a screengrab:

A cancelled eBay listing for the Amazon, by campaigners at @wdmuk who don't dig pricing nature: twitter.com/adamvaughan_uk…

— Adam Vaughan (@adamvaughan_uk) June 20, 2012

5.38pm: A female protester, reportedly wearing a Clegg mask, interrupts the deputy prime minister during his opening speech at the World Bank side event on natural capital, according to reports from Rio+20:

Activist escorted out of the venue wearing a nick Clegg mask. The real Clegg stoically continues #RioPlus20

— Kirsty Schneeberger (@KristaSpright) June 20, 2012

Clegg says that without the right tools to measure the right things you can't have sustainable development, and he declares that greenhouse gas emissiojn reports are to be mandatory from all companies on the London Stock Exchange.

Here's some more Twitter coverage from people at the briefing, including the Guardian's Jo Confino:

Nick Clegg: Natural Capital Accouting may seem quite dry as a subject but it is supremely important #Rioplus20

— Jo Confino (@joconfino) June 20, 2012

Nick Clegg: "natural capital massively undervalued. That problem is as much psychological as anything else" #Rioplus20 bit.ly/LB3lRr

— Jo Confino (@joconfino) June 20, 2012

Norwegian Prime Minister Stoltenberg "How we measure nature is one of the most important political questions we are facing" #NCDialogue

— Natural Capital (@NCDeclaration) June 20, 2012

5.43pm: In case you want to read more on what exactly natural capital is, here are a couple of good pieces we've run on it from my colleagues Damian Carrington (broadly in favour, in principle) and George Monbiot (deeply against it).

Here's an excerpt from Carrington:

Putting price tags on nature feels deeply wrong, but today's world with no price tags is failing miserably to protect nature. That is why the independent National Ecosystem Assessment published today by the UK government is truly significant. For the first time for any nation, it pins specific price tags onto the many economic, health and social benefits the natural world currently provides for free.

And Monbiot:

It's the definitive neoliberal triumph: the monetisation and marketisation of nature, its reduction to a tradeable asset. Once you have surrendered it to the realm of Pareto optimisation and Kaldor-Hicks compensation, everything is up for grabs. These well-intentioned dolts, the fellows of the grand academy of Lagado who produced the government's assessment, have crushed the natural world into a column of figures. Now it can be swapped for money.

5.46pm: Our news story on the UN secretary general's spin on Rio is up now. Here's the top:

Ban Ki-moon, the secretary general of the United Nations, called on world leaders to step up their political commitment to sustainability on Wednesday, as he opened the Rio+20 Earth summit with an acknowledgement that negotiations have so far failed to live up to hopes.

More than 100 world leaders and senior ministers, including the Chinese premier Wen Jiabao, US secretary of state Hillary Clinton and UK deputy prime minister Nick Clegg, are attending the mega-summit, which has been billed as a once-in-a-generation opportunity to rebalance economic growth, social stability and environmental protection.

However, many delegates and NGOs have expressed dismay at the watered-down outcome document that was agreed by member states ahead of the summit.

5.54pm: Jonathan Watts reports on Clegg's opinion of the text that's been agreed by 191 countries:

Nick Clegg. Photograph: Anna Gowthorpe/PA

"This represents a real step forward. It may not be as ambitious as if I had written it myself...But by definition, any text that brings together 190 countries will always involved dilution...The key is what direction does this point us towards. My view is that the text assembled by the hosts pushes us all towards a world where we treasure, measure and protect sustainable development in a way we have never done before."

He then went on to talk about the Natural Capital Accounting initiative, at which point he was heckled by a masked protester who was lead away shouting, "We're selling off natural resources for profit. This is a way for big corporates to take land from indigenous people."

Clegg announced that UK would be the first country to get companies on the Stock Exchange to do green reporting (see the story and comment piece we ran earlier), which earned generous applause.

Clegg said. "For too long we have valued the wrong things and undervalued natural resources on which we all depend. Unless we move towards a more holistic picture, we'll repeat the mistakes of the past."

Announcing that 50 governments and 50 companies have signed up to a Natural Capital Accounting declaration, he said if governments can move beyond GDP in 15 and 20 years time to use a measure that values long term prosperity, then "we can genuinely start changing things for good."

6.04pm: I'm signing off for today, but we'll run a new liveblog covering all the latest developments on Thursday. For now, I'm going to leave you with this photograph taken earlier today.

It's of Nick Clegg looking wistfully up at Rio's Tijuca Forest.