How can greenhouse gases harm us?
What are greenhouse gases? At the low concentration levels scientists are talking about, they don't actually harm us directly - its the indirect warming of the planet and changing the climate that's the problem.
Greenhouse gases including
Together they have produced the natural greenhouse effect that has kept the planet around
The problem is that humans are burning more and more fossil fuels that release
We are essentially putting the natural greenhouse effect "on steroids" and the average annual temperature of the planets is rising ever decade.
Scientists have warned that the greenhouse effect should not climb higher than
The impacts of a warming world are: more wild weather to come, melting the big ice sheets that will flood many coastal cities, disruption to food supplies, more intense heat waves, more droughts, and in general, more lives lost. You can read about the scary example of Bangladesh here and the Alaskan village that already needs to be relocated here.
There are also indirect ways in which global warming will harm humans. For example, species will go extinct that may have been useful to humans or were critical to an ecosystem. Other species may spread to areas that were previously not suited for them and may act as pests, destroying crops or spreading disease.