It's over four years since the Paris Agreement was reached at the UN's COP21 climate summit.

It was in the French capital that world leaders committed to making sure global warming stayed "well below" 2 degrees Celsius above pre-industrial levels. They also agreed to pursue efforts to limit the temperature rise to 1.5 degrees Celsius.

In the time that's passed, the debate on climate change has intensified a great deal. Today, it's one of the most talked about and polarizing issues on the planet.

While activists decry what they perceive to be a lack of action when it comes to tackling the "climate emergency", national governments and big businesses claim they are making significant efforts.

This discussion is taking place against the backdrop of a "global energy transition," a shift from fossil fuel based energy sources to renewable ones. How fast this change will happen — and to what extent — is another part of the debate.