Global warming is a natural phase of Earth, caused by some Solar Activities by Sun. We human don't have to bother about it. Some of the environmentalist says that this is because of the CO2 we are emitting into the environment, but the reality is that we are just contributing towards 1% to 10% of actual global warming.
If the actual cause of Global Warming is CO2 emitted by the humans then why Global Warming occures on other planets. Just Google for "Global Warming on other planets" and see the results, there are no humans on other planets.
Having too little CO2 in the environment will cause for the plants to die more early, more over it also cools down the temperature on earth.
Having too much CO2 (obiviously, not caused by humans. Mostly generated in the Sea/Oceans) will lead to Green House effect and will lead in increasing the temperature on Earth.
So, the best is to plant more trees so that there would be a balance for the consumption of CO2 on the planet.
I personally think that instead of thinking on this baseless issue try to think on what if Nuclear War broke out in the world, it will destroy Earth more rapidly.
So, next time whenever somebody says you about global warming, just ignore it.