Coverage of Copenhagen climate conference
So, the UN climate conference COP15 finally gets under way in Copenhagen today. It's been a long time coming.
You can measure it from the UN climate change conference in Bali in 2007 where world leaders agreed to work on further efforts to reduce greenhouse gas emissions more widely and deeply than the 2005 Kyoto Protocol, and decided to meet in Copenhagen in 2009.
Or you can measure it from more recent events: the hours and hours of diplomacy this year preparing a draft treaty. Until even a few weeks ago, there was talk of a couple of thousand square brackets of unagreed text still being pored over by the politicians and their "sherpas" preparing the ground for the final gathering over the next two weeks.
Our job in the BBC newsroom has been to report on the build-up to the summit and to prepare our audiences to make sense of whatever happens. Now we aim to interpret the various negotiating positions and - if a treaty is agreed - to judge what it means for all of us.
Our specialist environment correspondents have been reporting on climate change - the science and the politics and the debate - for a long time. This year, for example, David Shukman has filed reports from the Arctic and Bangladesh on the changes to our climate and our planet. He was with scientists on the northern ice trying to measure its thinning, and in Bangladesh talking to those dealing with the effect of rising sea levels and looking at the analysis that links these to man-made climate change. Roger Harrabin has reported from China on the effect of warming and efforts to reduce emissions. And at his blog Earth Watch, Richard Black has built up a rich body of reporting and analysis.
The scientific background is not, of course, undisputed. The row about e-mails from the University of East Anglia's Climatic Research Unit shows how charged the debate can be. We were the first mainstream news organisation to report the story and have since drawn out three related but distinct threads. Are there question marks over the CRU's scientific work? Are there question marks about how it has handled its scientific data and engaged in public debate? Will the row affect Copenhagen?
There are those who answer the first question with a yes, and many more saying, like UK Climate Change Secretary Ed Miliband, that "one string of e-mails does not undermine the global science on climate change". The row has certainly raised the temperature leading up to Copenhagen, and the second question still needs an answer. In time, we'll report on the findings of the review of the incident and of a police investigation of the hacking or leaking.
This is because that's our main job here: to report what's going on. Our coverage of climate change comes under scrutiny and criticism too. We don't endorse one interpretation or another: we seek to report the range.
David Shukman last week, for example, reported on the variety of public opinion about how serious the threat of global warming is, and on the scientists who challenge the mainstream view. Our job is to help guide audiences and to report on where the centre of gravity lies in the debate, which is why he explained that the broad majority of climate change scientists accept that the evidence is clear that human activity has contributed to global warming. (See also Richard Black's look at sceptical objections and our feature The arguments made by climate change sceptics.)
It is complex stuff, and there are many questions for us all to try to understand. How much is the climate warming? Is it because of man's activities? How much might temperatures rise? And what can or needs to be done? Among those who support the scientific consensus - be they scientists, politicians or the wider public - there is still much debate about what to do - and that is what will be thrashed out in Copenhagen.
The world leaders who will gather in Copenhagen at the end of the summit will make their decisions informed by the Intergovernmental Panel on Climate Change (IPCC), a scientific body established by the United Nations Environment Programme and the World Meteorological Organization. It reviews and assesses the most recent scientific, technical and socio-economic work relevant to climate change. Governments are given the chance to scrutinise every word of the IPCC's main findings; delegations, including those from the Bush administration, endorsed the core conclusion that there is a 90% likelihood that most recent warming is man-made.
So the politicians are gathering because they believe something does need to be done to prevent rising temperatures affecting our planet and the people who inhabit it. The real argument is, then, over what to do about it. We've been covering the different approaches of various governments and varied public opinion around the world, such as today's World Service opinion poll on attitudes to climate change.
Whatever comes out of Copenhagen, there will be those who will say it is too little, and those who will say it is too much. Whatever governments sign up to, they will then have to take the case back to their publics and, where appropriate, their law-makers. So the debate will continue - as will our reporting.
Mary Hockaday is head of BBC newsroom.