This summary glosses over a lot of nuances and completely ignores all kinds of procedural issues. In one sense, this is a disadvantage. In another sense, you could fit this summary on one page. If you're interested in more details, follow some of the links.
You have probably heard that a group of states is suing the EPA over something involving global warming. There's a better-than-even chance that you're not clear on what the actual issue is, which is probably not your fault. This lawsuit is fairly complicated. Here's the simplest and shortest summary of what's going on that I can manage:
In 1970 Congress passed the Clean Air Act basically to reduce smog and make it easier for all of us to breathe. Under the Clean Air Act, the Environmental Protection Agency regulates emissions for things like sulfur dioxide that cause bad things to happen to you when you breathe them. If the EPA does not regulate emissions for such pollutants, citizens are allowed to sue to make the EPA create regulations.
The EPA essentially said it didn't think it had authority to regulate carbon dioxide and, if it did have the authority, it didn't feel like regulating carbon dioxide. The EPA does not consider carbon dioxide to be an air pollutant—at least not the kind of air pollutant the Clean Air Act is talking about.
Unfortunately, carbon dioxide is a greenhouse gas—so if enough of it is released, ice caps melt, polar bears die, and millions of people suddenly live underwater. Consequently a bunch of states have sued the EPA demanding regulations for carbon dioxide. (Note that the Environmental Protection Agency is not exactly on the environment's side.) The states argue that carbon dioxide is hazardous to human health because enough carbon dioxide can cause climate change, which can cause things like rising sea levels, which can cause flooding, which can be hazardous to human health. The actual language of the Clean Air Act is ambiguous enough that this might be a viable interpretation.
Generally the EPA gets to interpret the Clean Air Act however it wants. I suspect the EPA will win this particular legal case. This does not mean that the Supreme Court isn't worried about climate change—just that the Clean Air Act wasn't meant to deal with issues like global warming. Ideally, Congress would pass a new statute to deal with climate change. Because the Democrats are now in control of both houses of Congress, this statute could actually be passed. If the EPA wins this one, consider writing to your Congressman to help get things moving.