What is Obama's plan to tackle global warming?

President Obama's climate plan can ultimately be boiled down to a basic set of numbers. The United States is currently taking part in international talks to address global warming. And as part of those talks, the Obama administration has vowed that US greenhouse-gas emissions will decline 26 to 28 percent below 2005 levels by 2025.

That's... going to be tricky. As of 2013, US greenhouse-gas emissions had fallen just 8.5 percent below 2005 levels, mainly due to the recession, to a natural-gas boom that pushed out dirtier coal power, and to a rise in vehicle efficiency. But that's not enough, and emissions have recently begun creeping upward again:

So, to push emissions down further, the Obama administration has been proposing a slew of new rules and regulations through the Environmental Protection Agency — some of them quite sweeping and some quite controversial.

The list includes tighter fuel-economy standards for cars and trucks, strict carbon-dioxide limits for anyone who wants to build a new power plant, and a crackdown on methane emissions from oil and gas wells. None of this has gone through Congress — it's all being done under legal authority that the Supreme Court granted the EPA back in 2007.

And the most significant policy of all is arguably the Clean Power Plan: a huge new EPA program to reduce carbon-dioxide emissions from hundreds of existing coal- and gas-fired power plants nationwide. Under this plan, every state will get a specific goal for reducing emissions, and state policymakers can draft their own plans for how to get there, by shutting down coal in favor of gas, by boosting renewables and nuclear, improving efficiency, or even pricing carbon. It's up to them.

The administration is hoping that these efforts will spur other countries to respond in kind. Over the past year, China and Brazil have put out their own pledges for curbing emissions, and the goal is for all these proposals to get stitched together into a global climate agreement at UN talks in Paris in December 2015. One important debate, however, is whether all these efforts will be enough. Many environmentalists have questioned whether the US is moving fast enough to avoid 2°C of global warming — the widely agreed-on "limit."

What's more, Obama's plan has garnered plenty of heated opposition at home. Conservatives in Congress have tried to repeal Obama's climate rules at every turn (so far unsuccessfully), and industry groups are continuing to challening them in court. If a Republican wins the White House in 2016, he would likely have a fair bit of latitude to abandon the climate push — and weaken Obama's rules.

Why does Obama want to cut U.S. emissions 26 to 28% by 2020?

Back in 2009, at UN climate talks in Copenhagen, the world's nations agreed to limit global warming to no more than 2°C (or 3.6°F) above pre-industrial levels.

Staying below that 2°C limit will require most countries to cut their greenhouse-gas emissions drastically, but there's still a lot of disagreement on how to divvy up the responsibility. So, as an initial starting point, the Obama administration pledged to cut US emissions 17 percent between 2005 and 2020 — with the hope of negotiating more cuts with Europe, China, and other major emitters later on.

Now the Obama administration is going even further. The world's nations are hoping to negotiate a brand-new global climate agreement by the end of 2015, in which every single country would submit a voluntary pledge for cutting emissions. And as part of this new round of talks, the US government has said it will cut emissions 26 to 28 percent below 2005 levels by 2025.

Other countries have also made pledges, including China, Europe, Brazil, and so on. Some climate experts say these pledges are insufficient so far. Even if you add them all up, an analysis by Ecofys found, the world is likely to heat up more than 3°C (or 5.4°F) above pre-industrial levels by the end of the century.

Why have US carbon dioxide emissions fallen since 2005?

US greenhouse-gas emissions have fallen roughly 8.5 percent between 2005 and 2013:

There are a couple of big reasons for this drop:

There was a massive recession in 2008, which meant less economic activity and less energy use. That drove US emissions down for a few years.

Americans have been driving less since 2005. They've also been buying more fuel-efficient cars and trucks in response to new fuel-economy rules by the Obama administration.

have been driving less Electric utilities have been using less coal to generate power, in part because a domestic boom in shale drilling has led to a glut of cleaner natural gas. (Burning natural gas for electricity produces roughly half the carbon-dioxide that burning coal does.) Cleaner wind power has also become a bigger source of electricity in recent years.

Energy analysts don't expect these trends to last forever, though. As the economy continues to recover, emissions are projected to go back up — unless new policies are put in place.

What are Obama's specific climate policies?

Here's a list of the major actions the Obama administration has taken on climate change. Most of them have been carried out through the Environmental Protection Agency:

The EPA's endangerment finding: Back in 2007, the Supreme Court said the EPA was required to regulate carbon-dioxide under the Clean Air Act so long as there was evidence that the gas endangered public health and welfare. In 2009, the EPA laid out the scientific case for why this was so — the so-called "endangerment finding."

Fuel-economy standards: As a first step, the EPA began regulating emissions from vehicles. Under a series of rules, fuel-economy standards will slowly rise until all new cars and light trucks sold in the United States average roughly 35.4 miles per gallon on the road by 2025.

Permitting for large industrial facilities: Any new-or newly upgraded-industrial facility that's likely to emit more than 100,000 tons of carbon-dioxide per year has to first get a permit from the EPA and adopt the best available technology for reducing emissions.

CO2 regulations for new power plants: The EPA has also proposed that anyone who wants to build a new coal- or gas-fired power plant will have to meet certain emissions standards. Modern combined-cycle gas plants already meet the proposed standard. But the rules may make it impossible to build a new coal plant in the United States unless it can capture its own emissions and bury them underground (a still-nascent technology).

The Clean Power Plan: This is a big one. In June 2014, the Obama administration proposed new rules to limit carbon-dioxide emissions from the nation's existing fossil-fuel power plants. The EPA will set individual emissions goals for each state and leave it to state policymakers to decide how to get there — via efficiency, switching from coal to gas, investing in renewables, or other options. The proposed rule was expected reduce power plant emissions an estimated 30 percent below 2005 levels by 2030.

Fuel-economy rules for heavy-duty trucks. The EPA has also put out a series of rules to reduce emissions from heavy trucks, buses, and vans — which account for roughly 20 percent of gasoline use in the United States. These standards will slowly ratchet up between 2014 and 2027.

Methane regulations. The Obama administration has proposed policies to curtail methane leaks from all new oil and gas wells. Methane is a potent greenhouse gas, though the exact scale of the leaks from natural gas infrastructure is still being determined. As yet, the EPA has not imposed regulations on existing wells, which are estimated to be the source of 90 percent of all leaks.

Complementary policies. Meanwhile, the White House is hammering out an agreement with China and other countries to phase out hydrofluorocarbons (HFCs), another set of greenhouse gases used in everything from soda machines to many car air conditioners. The Energy Department has been setting new energy-efficiency standards for appliances and buildings. The Interior Department is trying to speed up wind- and solar-power development on publicly owned lands. And foreign-aid agencies have stopped financing coal plants overseas (except when there are no possible alternatives).

Back in 2013, the White House outlined its climate agenda in full here.

What are the CAFE standards for cars and trucks?

Every year, car manufacturers in the United States have to meet fuel-economy standards for the cars, SUVs, and light trucks they produce. The Obama administration has been ratcheting up these standards over time.

How the standards work now: Companies are free to produce whatever mix of gas-guzzling SUVs and smaller, more efficient cars each year. But the average fuel economy of their entire fleet must meet a certain threshold — or else the manufacturers have to pay a penalty. This is known as Corporate Average Fuel Economy, or CAFE. These standards were first enacted in 1975.

What Obama did: The Obama administration has been steadily raising these CAFE standards over the years. In 2011, the standard was 27.5 miles per gallon for all new cars and light trucks sold that year. The standard will keep rising each year until it hits 54.5 miles per gallon in 2025:

Now, the new cars and light trucks sold in 2025 won't actually average 54.5 miles per gallon on the road. That's because the tests to measure CAFE standards don't always do a perfect job of replicating real-world conditions. On the road, the average fuel economy for new cars and light trucks will be around 35 miles per gallon in 2025.

Oil savings: The Energy Information Administration estimates that the stricter rules will cut US oil consumption by about 2.2 million barrels per day by 2025. (The US currently consumes about 19 million barrels of oil per day.)

How automakers will meet them: Automakers are expected to meet the standard by both reducing the weight of vehicles and by employing "micro-hybrid" technology that automatically conserves fuel when the car is idle. They can also produce more electric vehicles and hybrids to help meet the standard.

Criticisms of the rule: Critics of CAFE standards point out that they make vehicles more expensive. Defenders usually counter that drivers save money on gasoline and come out ahead in the long run. Economists, meanwhile, argue that if you really want a policy that curtails gasoline use, then raising the gas tax is a more cost-effective measure. (A gas tax is, however, far less popular politically.)

What are EPA's carbon dioxide rules for new power plants?

In 2013, the Environmental Protection Agency (EPA) proposed new limits on carbon-dioxide emissions from all future coal and natural-gas power plants built in the United States. The proposed rules would essentially make it impossible to build new traditional coal plants. Here's how the rules break down:

Natural gas plants: Under the proposed standards, all future large natural-gas power plants can produce no more than 1,000 pounds of carbon-dioxide for every megawatt-hour of electricity produced. Most modern combined-cycle gas plants can already meet this standard, so this shouldn't have much impact.

Coal plants: All future coal plants, meanwhile, can emit no more than 1,100 pounds of carbon-dioxide per megawatt-hour. That's a bigger deal, because the average coal plant in the United States currently produces about 1,768 pounds of carbon-dioxide per megawatt-hour — well above the standard.

This means that utilities will only be able to build new coal plants if the plants can capture 20 to 40 percent of the carbon they produce and bury it underground. That technology is still in its infancy. So a lot hinges on whether carbon capture and storage technology will ever become viable. The EPA thinks this is possible — and that this rule will accelerate the technology. The coal industry thinks that carbon capture is still far off and that the rule needs to be modified.

Projected impacts: In practice, this rule isn't likely to have much effect in the short term one way or the other. Electric utilities had stopped building new coal plants anyway — in part because natural gas is currently a cheaper alternative.

The EPA expects this rule to have little effect on either energy prices or US emissions. It basically solidifies the status quo. But there's a catch: If natural gas should become unexpectedly expensive, the proposed rule would make it very hard for utilities to build new coal plants in the future to supply electricity.

What is the Clean Power Plan?

On June 2, 2014, the EPA proposed a new rule to reduce carbon-dioxide emissions from the nation's existing fossil-fuel power plants — the first of its kind.

Under the rule, the EPA will set different emissions targets for 49 states, based on their existing energy profile. (Vermont is exempted because it has no fossil-fuel electric plants.) Each state will then have to reduce their rate of emissions a certain amount by 2030.

When taken together, the EPA estimates these state plans will cut carbon-dioxide emissions from the nation's power sector as much as 30 percent below 2005 levels by 2030. (Power-plant emissions have already fallen about 15 percent between 2005 and 2013, so we're halfway there.)

States will have a lot of flexibility to pursue policies to reach their goals. They can use more efficient technology at coal plants, switching from coal to natural gas, boosting their use of solar or wind or nuclear power, or even joining regional cap-and-trade systems that require companies to pay to emit carbon-dioxide.

The final regulation will take effect in August 2015. States will then have until June 2016 to draw up plans to implement the rule (although they can apply for extensions or get more time if they're working together on regional plans).

There's a lot at stake here. Coal and natural gas plants were responsible for about 38 percent of all US carbon-dioxide emissions in 2012:

Sources of US carbon dioxide emissions 2012

Will Obama actually meet his climate goals?

That's still unclear.

Remember, the Obama administration has set a goal of reducing US greenhouse-gas emissions 17 percent below 2005 levels by 2020 — and then at least 26 percent below 2005 levels by 2025.

We're not quite on track quite yet. So a recent analysis by the World Resources Institute took a look at some of the additional policies that could help hit those goals:

The conclusion? Sure, both Obama and the next president could put the United States on track to hit its target through executive actions alone (i.e., without Congress). But it will take more steps than Obama's taken so far — and a lot depends on the next president.

The key steps: The Clean Power Plan to reduce carbon emissions from power plants would have to get finalized and implemented. The Energy Department would have to strengthen efficiency standards for household appliances and boilers further. Either Obama or the next president would have to strengthen programs to crack down on HFCs. The EPA would also have to begin regulating carbon-dioxide emissions from industrial sources such as refineries and chemical plants. The agency would also have to crack down on methane leaks from existing oil and gas wells and reduce methane leaks from landfills.

That's a lot to do. All of those rules would have to withstand legal challenges from industry. And a lot depends on the 2016 election. If a Republican wins the White House and decides he doesn't want to do any of this, then US greenhouse gas emissions won't neccessarily keep falling.

Is Obama waging a "war on coal"?

Coal has been declining sharply in the United States. Back in 2003, there were 629 coal-fired power plants nationwide. Today, that's down to 491 and falling. And hundreds of additional coal units are at risk of retirement in the years ahead:

There are three big reasons for this:

1) The fracking boom in the late 2000s created a glut of cheap natural gas (a cleaner competitor to coal), and many electric utilities have been switching over. This has undeniably been a major factor.

2) New EPA rules from the Obama administration on pollutants like mercury, sulfur-dioxide, and particulates are also putting pressure on utilities. Many coal plant operators are choosing to shutter their older units rather than install costly new control technology. And that's before the Clean Power Plan to reduce carbon-dioxide emissions from coal plants takes effect, which will impose further costs.

3) On top of this, the Sierra Club has been waging an effective campaign to persuade local utility regulators to retire their coal plants by 2020 rather than incur endless cleanup costs.

Republicans and industry groups often focus on Obama's environmental rules, arguing that he's waging a "war on coal." But that's only part of the story. As several analyses have found, many of these plants would be at risk even without these rules — the shale boom has made them uneconomical.

How are Republicans reacting to Obama's climate policies?

Most Republicans in Congress are sharply opposed to Obama's climate policies (as are a number of Democrats from coal states, like Sen. Joe Manchin of West Virginia).

House Republicans have tried multiple times to block the Environmental Protection Agency from regulating carbon dioxide. Those resolutions haven't yet made it through the Senate, and Obama has vowed to veto them, but the GOP will likely keep trying.

The arguments against the rules vary. Many in the GOP deny that climate change is even real. Others argue that these rules will continue to cripple the coal industry. Still others point out that the Obama administration's CO2 standards would require new coal plants to adopt a technology — carbon capture and storage — that isn't even commercially viable yet.

Republicans have also charged that Obama isn't doing enough to spur fossil-fuel development in the United States. Among other things, they've called for more drilling on public lands and the approval of the Keystone XL pipeline.

What is the Keystone XL pipeline?

The Keystone XL pipeline is a controversial pipeline system to transport oil from Canada's oil sands down to refineries in the Gulf Coast.

The Obama administration is still mulling whether to approve the northern leg of the project, which would transport 730,000 barrels of oil per day from Alberta, Canada, to Steele City, Nebraska. Since the pipeline would cross the US-Canada border, the State Department has to approve it first.

Arguments for the pipeline: Oil companies and the Canadian government want the pipeline approved. Over the last decade, they’ve started extracting oil from Alberta’s tar sands — a gooey mix of sand, clay, and oil. But they’re finding it difficult to ship all that oil to refineries who can turn it into usable fuel. The pipeline would help with that, by offering cheaper connections to refineries down in Texas.

Labor unions also back the project: A State Department review estimated that the pipeline would support 42,000 jobs over its two-year construction period (that's about 35 permanent jobs, 3,900 temporary construction jobs, and the rest support jobs or indirect jobs resulting from employee spending). The project would contribute roughly $3.4 billion to the economy.

Meanwhile, one 2013 poll found that 66 percent of Americans support the project.

Arguments against the pipeline: Green groups, on the other hand, are asking Obama to block the pipeline. They point out that producing oil from Canada's tar sands is a particularly energy-intensive process that leads to 17 percent more carbon dioxide than regular oil production does over the entire life-cycle.

That, in turn, will exacerbate global warming — especially at a time when the world will likely need to leave much of its existing oil, gas, and coal reserves underground if we want to avoid drastic climate change. Better to block tar sands development, green groups say say, and start shifting toward cleaner energy alternatives.

Obama's position: President Obama has said that he would only approve Keystone XL if the project does not "significantly exacerbate" carbon-dioxide emissions, which arguably leaves him some wiggle room. It's not clear when a final decision will come. For more on this debate, see our comprehensive Keystone XL explainer.

Could Obama's climate plan get blocked in courts?

Parts of it could, yes. Industry groups and various states have been suing the EPA every time it puts out a new rule on carbon dioxide. So far, the agency has fended off all of these challenges, but it's unlikely that the lawsuits will end anytime soon.

The Clean Power Plan, which will regulate carbon dioxide from power plants, is likely to come under heavy scrutiny. Because it's such a novel program under the Clean Air Act, there's always some legal risk involved.

Nathan Richardson of Resources for the Future has written a nice primer on the issues here. The short version: there's a chance that the Supreme Court could uphold the entire rule, strike down the entire rule, or weaken the emissions goals that the EPA sets for individual states. The Obama administration is confident that the rule will survive, but we'll have to see.

Are there other ways to reduce emissions?

Yes. Many economists would say that putting a price on carbon-dioxide and letting the market figure out how best to cut emissions is the ideal policy for tackling global warming.

That could include a carbon tax, where the government sets a fee tax on oil, gas, and coal — giving companies an incentive to use less or seek out alternatives. It could also include a cap-and-trade system, which is more elaborate. Congress would need to approve any policies like these, however, and Congress doesn't seem inclined to do much about climate change right now. (A cap-and-trade bill failed in the Senate in 2010.)

The White House has said it would be open to alternative policies to tackle global warming. President Obama has, for instance, proposed a clean energy standard that would require utilities to get a greater portion of their electricity from renewables. And Joseph Aldy, a former White House adviser, has said that Obama would be open to a carbon tax if Republicans were willing to negotiate. So far, however, those proposals have gone nowhere.

Can the US solve global warming on its own?

No. The United States is only responsible for about 17 percent of the world's annual greenhouse gas emissions. So even if Americans stopped polluting altogether, that wouldn't be enough to stop climate change.

One way to see this is through coal exports. Right now, the United States is using less and less coal each year — thanks to an abundance of cheap natural gas and new pollution regulations. But that coal isn't just sitting in the ground. Instead, mining companies are shipping it off to Asia, where it's getting burned in Chinese power plants.

So any serious attempt to mitigate global warming would have to involve all the major emitters — not just the United States, but Europe, China, India, and so forth. That's the aim of ongoing international climate talks.

Obama administration official officials have suggested that setting a goal of cutting emissions 26 to 28 percent below 2005 levels by 2025 could help push those global talks along. Among other things, they cite the fact that China made its own promise to curb emissions by around 2030 earlier this year.

Yet other groups are skeptical that the United States — or any country — is doing enough. Consider this analysis from the Climate Action Tracker, which keeps tabs on commitments on emissions by various countries. That group finds that the United States would need to cut emissions more like 40 percent by 2025 if the world wants a shot at keeping global warming below 2°C. (And developing countries would have to respond with their own significant reductions.)

Will the US need to adapt to global warming?

Yes. Even if the world could zero out its emissions tomorrow, we've already loaded enough carbon-dioxide into the atmosphere to raise global temperatures by more than 1°C over pre-industrial levels. And even a mild temperature increase will likely mean things like more heat waves and higher sea-level rise. So that means adaptation.

Climate-change adaptation can take a variety of forms. In the United States, Louisiana has written up a plan to restore and protect its coastline from further erosion at the hands of sea-level rise over the next 50 years. Texas is trying to improve its drought-response plans. Governors out West have begun talks on how global warming might affect water allocation in the Colorado River. New York City has to think about how to deal with fiercer storm surges in the years ahead as ice sheets melt and sea levels rise.

But, so far, many countries aren't very far along. A comprehensive survey from October 2012 finds that some states and cities around the United States are beginning to draw up plans, but they're nowhere near adequate. "Most adaptation actions to date appear to be incremental changes," the survey notes, "not the transformational changes that may be needed in certain cases to adapt to significant changes in climate."

The White House has set up a "task force" that's supposed to help state and local agencies prepare for the impacts of climate change that are lurking in the near future, such as sea-level rise or flooding or extreme weather. One example: All federally-funded rebuilding after superstorm Sandy will have to take the risks of future flooding into account.

Does the US have a climate plan for after 2025?

Not at the moment.

Right now, the Obama administration is hoping to cut US greenhouse-gas emissions 26 to 28 percent below 2005 levels by 2025. It's unclear whether the US can meet that goal. And it's especially unclear what happens after that.

If the world were serious about limiting global warming to below 2°C, then the US would likely need to cut emissions 80 percent by mid-century. (This is assuming other countries like China and India also agreed to cut.) And, right now, there's no plan for those longer term cuts.

A recent open letter by the Clean Air Task Force, a US think tank, noted that future cuts in emissions would require more than EPA regulations alone. Clean-energy technology will have to improve vastly as well. "Ultimately," the letter notes, "we will need to capture the carbon from gas-fired power plants as well. Renewable energy faces challenges of scale, cost and intermittency; carbon capture and storage faces cost challenges at full scale; and current forms of nuclear power are challenged by safety, waste management, weapons proliferation and cost risks."

What else should I read about Obama's climate plan?

Here's the full list of climate proposals the White House has laid out.

The Environmental Protection Agency has a full list and description of all the regulations that it is taking on climate change here.

For a liberal view, Jonathan Chait has argued in New York Magazine that Obama's climate-change agenda is far more ambitious than most people think. For a conservative view, here are criticisms of Obama's agenda from the Heritage Foundation.

Ryan Lizza wrote a long feature in The New Yorker on Obama's thinking on the Keystone XL pipeline that offers a good sense of how the White House thinks about climate change.