Why 1.5 degree Celsius?

You might have read somewhere that there is a consensus around the idea that in order to avoid severe consequences from climate change, we need to keep global average temperature increase at or below 1.5 degree Celsius compared to pre-industrial levels. We are talking about The Paris Agreement, which is a legally binding international treaty on climate change. It was adopted by 196 Parties at COP 21 in Paris, on 12 December 2015 and entered into force on 4 November 2016.

The question is, why 1.5 degree Celsius? What is the difference between 1.5 and 2 degree Celsius of global warming?

Please spend some time to study the graphic below which was taken from an IPCC report on global warming of 1.5 degree Celsius, showcasing how risks across a whole spectrum of systems we care about dramatically increase as temperatures increase.

As can be seen from the graph, the risks of catastrophic impacts greatly increase at temperatures greater than 1.5 degree Celsius.

World Wide Fund also created another graph to compare different levels of impacts between 1.5 and 2 degree Celsius of global warming.

The above graph points out that even half a degree makes a huge difference. Imagine what could happen if global average temperature increase above 2 degree Celsius?