OK, to TOMMY, global warming is NOT a theory, it is a fact. The "greenhouse thingy" you mention is the theory part, if you can call that theory because it's based on experiments and hypotheses proved. There is enough fact to prove that global warming IS happening.
SO, to answer, you know this global warming "thing" is cyclic. Gases get trapped, so everything becomes warmer, so oceans emit vapors and more gases, so everything becomes warmer still...
Both rich and poor countries need to save as big a sum of money as they can for dealing with reducing their impact on climate change and to prepare themselves for the oncoming problems in almost every area, like their economy, their agriculture (and so their sustenance), their population's health...Rich countries should immediately reduce their harmful gases emissions and try to change their energy sources to renewable, unharmful ones as fast as they can. Poor countries, well, it's a very difficult situation because they have almost no means with which they can prepare themselves for what's coming. Imagine their population increased, their resources diminished, and no money...
What we all need is careful planning and taking action as soon as possible, all heads together.