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World leaders are gathering in Paris, France, to try to hammer out a deal to tackle global warming.

Here's what we know and don't know about the Earth's changing climate.

The planet's climate has constantly been changing over time.

However, the world is heating up more quickly than in the past.

Many scientists believe that human activity is having a bad effect on global temperatures.

When we burn things like coal or oil to create energy to power things like homes, cars and factories, they release harmful gases.

These gases end up in the Earth's atmosphere and are trap more of the Sun's heat in and increase temperatures.

A few experts disagree and think that the effects of climate change are being exaggerated and that these changes happen naturally.

But to stop the effects of climate change, most climate scientists agree that humans will have to figure out a way to produce less harmful gas.

The full impact of climate change on the world is still uncertain.

Scientists say that if the planet's temperature eventually goes up by more than two degrees Celsius, sea levels will rise so much that low lying coastal areas and islands could end up under water.

Extreme weather like heatwaves, droughts and storms could happen more often and become more severe, and a third of all animal species could be wiped out.

Poorer countries, which don't have the money to deal with rapid change in temperatures, could suffer the most.

Some experts believe that we are already half way to this point and action needs to be taken now.

Discussions in Paris will be based around how to slow down greenhouse gases that are pushing up global temperatures and causing damage to planet earth.

The conference, which lasts for 11 days, will try to get countries all around the world to agree on a plan to stop things getting any worse.

People are hoping that world leaders in Paris will be able to make a long term plan to limit the damage caused to the planet by climate change.

They will try to find a way to slow the rising temperatures by focusing on renewable types of energy like wind, solar and wave power, and reducing energy waste.

Rich countries like the UK and USA have promised to help poorer ones, but they disagree about the amount of money on offer.

It's hoped that the Paris talks will lead to countries agreeing on ways to make sure the temperature on the earth doesn't rise too quickly and too high.