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The US has just taken its first significant step towards cutting its greenhouse gas emissions. It has set targets to cut carbon emission from existing power plants.

Forget all the gobbledegook: we鈥檒l explain what today鈥檚 announcement really means.

Sorry, what has happened?
Last year, US president Barack Obama asked the (EPA) to come up with a plan to cut carbon dioxide emissions from existing power plants. The agency has just . It says that by 2030, emissions from power plants that are in operation today will have to be cut to 30 per cent below 2005 levels.

Oh, so it鈥檚 just power plant emissions. How significant is that?
Pretty significant. They account for 40 per cent of US emissions.

I thought there wasn鈥檛 any hope that the US would ever regulate emissions?
Passing new laws on climate change has been鈥� difficult. In the current political climate, a law that sets an overall cap on US emissions, as exists in Europe, would never pass. There鈥檚 simply too much opposition from the Republicans.

However, there has always been a back door, and that is the . It makes the EPA legally responsible for regulating pollutants like mercury and CFCs. Obama has always said that he would use this if he couldn鈥檛 pass a new climate bill.

Last September, for example, the EPA proposed carbon pollution standards for future power plants, saying they should emit no more than 500 kilograms of carbon dioxide per megawatt-hour, well below current averages. These measures are key components of Obama鈥檚 Climate Action Plan.

Using legislation like that sounds a bit like political trickery.
If it is, it鈥檚 trickery approved by the highest court in the land.

Back in 2007, 12 states sued the EPA in a court case known as . The states claimed that CO₂ is harmful to human health, and because the Clean Air Act requires the EPA to regulate all pollutants that 鈥渕ay reasonably be anticipated to endanger public health or welfare鈥�, the EPA was obliged to regulate CO₂. The case went to the Supreme Court, and the states won. Today鈥檚 announcement is just the long-awaited result of that lawsuit.

So, power plants will need to spend money on cleaning up their pollution?
Yes.

How are they going to do that?
It is up to state governments. Today鈥檚 proposal leaves it up to them to decide how they want to tackle the problem.

Most experts agree that the most cost-effective approach is to first increase energy efficiency 鈥� so, more efficient light bulbs and appliances. The US is not known for being economical with its energy usage. Other measures could include boosting renewables or, for coal-fired power stations that produce a lot of CO₂, introducing carbon capture and storage.

Won鈥檛 that just make electricity bills go up?
You might think so, but several analyses say otherwise. For instance, the US published a report on Friday modelling the consequences of a similar target. They looked at a 36 per cent cut, and found that 鈥� saving an average of $109 per household across the US. A lot of that is down to improved energy efficiency: with help from their state, people will use less energy to heat and light their homes, which means fewer emissions from the power stations.

What about jobs? And won鈥檛 a bunch of power stations have to shut down?
Yes, that鈥檚 possible, and the coal lobby has been the main opponent to climate change legislation. On the other hand, reports suggest that there are already more people employed in the renewable energy field than in the coal industry, and boosting wind and solar will create more jobs. In , Obama said: 鈥淓very 4 minutes, another American home or business goes solar 鈥� and every panel is pounded into place by a worker whose job cannot be shipped overseas.鈥� The NRDC鈥檚 analysis of a 36 per cent emissions cut suggests it could create over 270,000 new jobs.

I don鈥檛 live in the US. Why should I care about this?
Because it should help the global effort to avoid dangerous climate change. Don鈥檛 underestimate what a strong US stance on cutting emissions can achieve.

International talks on climate change have been in deadlock for about a decade. That鈥檚 largely because of conflict between rich nations 鈥� which historically emitted the most 鈥� and poor ones, which suffer the most because they can鈥檛 protect themselves from things like heatwaves and rising seas.

Some poor nations are now emitting lots of greenhouse gases, and China is now the world鈥檚 biggest emitter. Without a significant commitment from the US, China and these other countries won鈥檛 commit to cutting their own emissions.

In 2009, Obama made an international pledge to cut US emissions by 17 per cent below 2005 levels by 2020. Without a plan to cut pollution from power plants, that pledge will be almost impossible to meet.

OK, so now this plan is in place, we鈥檙e home and dry?
Er, no. It鈥檚 good news for the climate: today鈥檚 announcement is essential for the US to meet its 17 per cent pledge, and other nations are more likely to believe the US has good intentions if they can see real action. But many want to see bigger US cuts.

What鈥檚 next?
The plan now goes to consultation for one year, and will be finalised in 2015.

At this point you might be thinking that the Republicans will just revoke the plan. The thing is, Obama has a veto right that he can use to pass it, and he has said he won鈥檛 be shy with it. To overrule him, both the House of Representatives and the Senate need to drum up a two-thirds majority. With a Democratic majority in the Senate, that鈥檚 unlikely.