2 degrees Celsius

Keeping global warming below 2 degrees Celsius (3.6 degrees Fahrenheit) is a target for tackling climate change adopted by the UNFCCC at COP16 in 2010. As far back as the 1970s, scientists predicted that a global temperature rise of 2 degrees C would set in motion devastating and irreversible consequences. More recently, scientists have warned that around this temperature, ice sheets will begin to melt at an uncontrollable rate, resulting in massive sea level rise.

400 ppm

In March 2013, the global concentration of carbon dioxide (CO2) in the atmosphere stayed over 400 parts per million for a month for the first time in recorded history - and perhaps for the first time in 25 million years. Some scientists had considered this to be a milestone - albeit a negative one - for climate change. CO2 concentration of 400 ppm represents a rise of 85 ppm since measurements began in 1958. And scientists add that the rate of change is increasing to an alarming 2.75 ppm per year.

Adaptation

Many countries, particularly in the Global South, are already suffering from rising sea levels, droughts, floods and extreme weather events as a result of climate change. In order to cope, they need to build new infrastructure, protect homes and farmland, and switch to crops that can cope with the changing climatic conditions. A portion of the pledged climate finance (see below) is earmarked to help developing countries cover the costs of adapting to a warmer planet.

Carbon bubble

The carbon bubble refers to the idea that energy companies are vastly overvalued because share prices assume that business will carry on as usual. If governments were to enact the legislation needed to limit global emissions, the theory goes, their current business models would be blown apart, and many of their assets would be greatly devalued. If only 565 billion tons of CO2 were to be emitted instead of the possible 2,795 billion tons (see "carbon budget" below), the stock value of companies involved in coal, oil and natural gas would drop by an estimated $20 trillion dollars, according to some estimates.

Carbon budget

Scientists say that in order to stand a chance of keeping within the 2-degree Celsius limit, we may emit more than 565 billion tons of carbon dioxide by 2050. According to a 2010 report form the Carbon Tracker Initiative, potential emissions from all known reserves of coal, oil and natural gas amount to 2,795 billion tons - five times the "allowable" carbon budget. This would mean that 80 percent of unburned carbon should stay in the ground.

Carbon price

One approach to reducing greenhouse emissions is to make companies pay for every ton of CO2 they release into the atmosphere. The idea is to give industry an incentive to reduce their fossil fuel use, and make green alternatives more competitive. Cap-and-trade schemes like the European Union Emissions Trading System put a limit on emissions and issue allowances that companies can trade so they can pay for the right to emit more - or make a profit my emitting less and selling surplus allowances.

Climate finance

At COP15 in Copenhagen in 2009, richer countries committed to raising $100 billion per year by 2020 to support climate action in developing countries. This may be public or private money, and can take the form of loans. Much of it is channeled through the Green Climate Fund. Climate finance is seen as a key negotiating tool to get developing countries to commit to stronger action on emissions reduction.

COP21

The United Nations Climate Change Conference due to take place in Paris in December 2015 goes by the nickname COP21, shorthand for the 21st yearly session of the Conference of the Parties to the 1992 UN Framework Convention on Climate Change. The objective of the conference is to achieve an agreement to limit climate change and deal with its growing impacts.

Copenhagen Summit

The 2009 United Nations Climate Change Conference, known as COP15, has become a byword for failure and everything the Paris conference is trying to avoid. The summit aimed to produce a legally binding global agreement to fight climate change. But the Copenhagen Accord drafted at the end of the summit did not contain legally binding commitments to reduce carbon emissions and failed to be unanimously passed by all parties.

Decarbonization

The most efficient way to stop global warming is eliminate greenhouse gas emissions, the majority of which come from fossil fuels. However, such "decarbonization" of the economy is a huge challenge, with most of the world's energy and industry dependent on fossil fuels. Environmentalists are calling for the Paris agreement to include a long-term goal to completely end the use of fossil fuels - preferably by halfway through the 21st century.

Divestment

Divestment is the opposite of investment. In the context of climate change, this means pulling money out of companies involved in extracting or burning fossil fuels. Universities, charities, churches and pension funds have joined a global movement to divest from fossil fuel companies. The aim is to use consumer pressure to detract from such companies financially, though some argue that the real impact is in delegitimizing the business as a whole.

Emissions gap

Carbon reduction measures pledged by each country to date, if fulfilled (see "INDCs," below), are estimated to bring global temperatures to about 2.7 degrees Celsius. The overage of emissions, compared to the 2-degree target (see above), is referred to as the emissions gap.

Feedback loop

Rising temperatures have environmental impacts that in turn accelerate climate change. That's one reason scientists say we are heading for a tipping point, where impacts will intensify at an ever-faster rate. The most striking example is perhaps the melting of the Arctic ice sheets. The ice reflects back the sun's rays - an effect that diminishes as the ice sheets shrink, making the oceans heat up faster - in turn accelerating ice melt.

INDCs

Ahead of the COP21 Climate Conference in Paris, each individual member state was called on to submit its individual pledge to reduce carbon emissions. These "intended nationally determined contributions" (INDCs) have been criticized for lacking consistency and transparency, in addition to being non-binding.

Kyoto Protocol

The Kyoto Protocol was the first global agreement that set targets to tackle climate change by reducing carbon emissions. It was agreed in 1997 in Kyoto, Japan, but did not come into force until 2005. Under this agreement, only industrialized countries were bound to reduce their emissions. Yet key industrialized nations, like the US, refused to enact the treaty.

Loss and damage

Some impacts of climate change cannot be adapted to and have, or will have, a major impact on the economies of in poorer countries in particular. These countries are calling for extra compensation from industrialized nations that have been responsible for the bulk of greenhouse gas emissions to date.

Mitigation

Mitigation refers to measures to prevent global warming through reducing greenhouse gas emissions.

Ocean acidification

Much of the carbon released into the atmosphere is absorbed by the oceans. This causes a chemical reaction that produces carbonic acid, raising the water's pH and lowering levels of carbonate that many marine animals need for their skeletons and shells. The process also damages coral reefs.