The Copenhagen climate conference COP15 resulted in a document called the Copenhagen Accord. It was hammered out by a small group of countries - including the world's two biggest greenhouse gas polluters, China and the US. The conference as a whole did not adopt the accord, but voted to "take note" of it.
Was the summit a success?
This depends on your point of view.
On the positive side, the Copenhagen Accord, for the first time, unites the US, China and other major developing countries in an effort to curb global greenhouse gas emissions. The Kyoto Protocol did not achieve this - it imposed no obligations on developing countries to restrain the growth of their emissions, and the US never acceded to it. The accord also says developed countries will aim to mobilise $100bn per year by 2020, to address the needs of developing countries.
On the other hand, the summit did not result in a legally binding deal or any commitment to reach one in future. The accord calls on countries to state what they will do to curb greenhouse gas emissions, but these will not be legally binding commitments. Furthermore, there is no global target for emissions reductions by 2050 and the accord is vague as to how its goals - such as the $100bn of funds annually for developing countries - will be achieved.
What are the key points of the Copenhagen Accord?
• A commitment "to reduce global emissions so as to hold the increase in global temperature below 2C" and to achieve "the peaking of global and national emissions as soon as possible"
• Developed countries must make commitments to reduce greenhouse gas emissions, and developing countries must report their plans to curb greenhouse gas emissions to the UN by 31 January 2010
• New and additional resources "approaching $30bn" will be channelled to poorer nations over the period 2010-12, with an annual sum of $100bn envisaged by 2020
• A Copenhagen Green Climate Fund will be established under the UN convention on climate change, to direct some of this money to climate-related projects in developing countries
• Projects to reduce greenhouse gas emissions in developing countries will be subject to international monitoring if they are internationally funded
• Programmes to provide developing countries with financial incentives to preserve forests - REDD and REDD-plus - will be established immediately
• Implementation of the accord will be reviewed in 2015 and an assessment will be made of whether the goal of keeping global temperature rise within 2C needs to be strengthened to 1.5C
Which countries backed the accord?
The essential points of the deal were brokered by US President Barack Obama with representatives of China, India, Brazil and South Africa. Mr Obama also consulted with the leaders of France, Germany and the UK. Most countries at the conference gave it their support, but some countries were resolutely opposed, including Venezuela, Bolivia, Ecuador and Cuba.
Why did the Copenhagen summit take place at all?
The majority of the world's governments believe that climate change poses a threat to human society and to the natural world.
Successive scientific reports, notably those from the Intergovernmental Panel on Climate Change (IPCC), have come to ever firmer conclusions about humankind's influence on the modern-day climate, and about the impacts of rising temperatures.
In 2007, at the UN climate talks held in Bali, governments agreed to start work on a new global agreement.
The Copenhagen talks marked the end of that two-year period.
Why is a new global agreement needed?
The Copenhagen talks sat within the framework of the UN Framework Convention on Climate Change (UNFCCC), established at the Rio de Janeiro Earth Summit in 1992.
In 1997, the UNFCCC spawned the Kyoto Protocol.
But neither of these agreements can curb the growth in greenhouse gas emissions sufficiently to avoid the climate impacts projected by the IPCC.
In particular, the Kyoto Protocol's targets for reducing emissions apply only to a small set of countries and expire in 2012.
Negotiations therefore began on new treaty that was bigger, bolder, wider-ranging and more sophisticated than the Kyoto agreement, and the plan was that these would conclude in Copenhagen.
Why is climate change happening - and is it the same as global warming?
The Earth's climate has always changed naturally over time.
For example, variability in our planet's orbit alters its distance from the Sun, which has given rise to major Ice Ages and intervening warmer periods.
According to the last IPCC report, it is more than 90% probable that humankind is largely responsible for modern-day climate change.
The principal cause is burning fossil fuels - coal, oil and gas.
This produces carbon dioxide (CO2), which - added to the CO2 present naturally in the Earth's atmosphere - acts as a kind of blanket, trapping more of the Sun's energy and warming the Earth's surface.
Deforestation and processes that release other greenhouse gases such as methane also contribute.
Although the initial impact is a rise in average temperatures around the world - "global warming" - this also produces changes in rainfall patterns, rising sea levels, changes to the difference in temperatures between night and day, and so on.
This more complex set of disturbances has acquired the label "climate change" - sometimes more accurately called "anthropogenic (human-made) climate change".
Will the Copenhagen deal solve climate change?
The global average temperature has already risen by about 0.7C since pre-industrial times.
In some parts of the world this is already having impacts - and a Copenhagen deal could not stop those impacts, although it could provide funding to help deal with some of the consequences.
Greenhouse gases such as CO2 stay in the atmosphere for decades; and concentrations are already high enough that further warming is almost inevitable.
Many analyses suggest an average rise of 1.5C since pre-industrial times is guaranteed.
Tough action to reduce emissions might keep the temperature rise under 2C; but given uncertainties in how the atmosphere and oceans respond to rising concentrations of greenhouse gases, it might not.
This is why developing countries put such an emphasis on adaptation, which they argue is necessary already.
IPCC figures suggest that to have a reasonable chance of avoiding 2C, global emissions would need to peak and start to decline within about 15-20 years.
Currently, the cuts pledged by industrialised nations are not enough to halt the overall global rise in emissions. Furthermore, countries that went in to the Copenhagen conference prepared to offer bigger cuts in emissions if other countries took tough action, appear to be sticking with pledges to cut emissions at the lower end of their range.