Since the dawn of the industrial revolution, the richest countries on Earth together with the biggest corporations have build their wealth by consuming the natural resources and by emitting enough green house gases to trigger a climate change. During this process they took advantage of the poor countries by exploiting their cheap workforce and by depleting their resources.
Now that we are at the brink of planetary chaos and climate change is almost imminent, the first people who are going to suffer are still the poorest ones. The native, the small farmers and poor people all over the world will be the first affected ones by depleting water sources, increased number of violent weather phenomena or by rising water levels. Although these changes were brought on by the rich, the consequences will be paid by the poor. This is climate debt that the western world has to pay to developing countries.
What will the first world governments do? Will they welcome the tens of millions of refugees which will be displaced by climate change? Will they give out money to poor countries in order to defend themselves against natural disasters? Most likely not. They would rather give money to support inefficient corporations just to keep them on the floating line. This is why the people have to take action and to determine governments to pay their climate debts.