"There is such a thing as being too late when it comes to climate change," Pres. Barack Obama said in unveiling the administration’s Clean Power Plan at the White House on August 3. "The science tells us we have to do more."

An analysis by Scientific American suggests that the president is right: the Clean Power Plan alone is not enough. The plan, which goes into effect in 2022 and aims to reduce U.S. greenhouse gas emissions by 32 percent by 2030, will lock in an energy transition that is already underway. But the roughly 1,000 fossil fuel–fired power plants in the U.S. will largely continue to operate as usual, using some combination of efficiency improvements, emissions trading and offsets to meet Clean Power Plan state targets.

"Coal and natural gas will remain the two leading sources of electricity generation in the U.S." the plan admits. Together, the fossil fuels are anticipated to provide roughly 60 percent of U.S. electricity in 2030, or just 7 percent less than the amount generated from those same fuels in 2014. The U.S. Environmental Protection Agency expects natural gas to predominate, displacing coal as the number-one fuel for power generation.

But natural gas has already displaced coal over the past decade, cutting U.S. CO2 emissions from the electricity sector by roughly 16 percent. That's half of the ultimate total reduction the Obama administration expects under the Clean Power Plan—a full seven years before the program even begins. In other words, the plan is really a way to ensure that the U.S. power industry doesn’t backslide into more polluting forms of electricity generation.

The plan relies on three basic options to lock in and drive future reductions: improving the efficiency with which power plants burn coal; swapping natural gas for coal; or replacing electricity generated from burning fossil fuels with electricity generated from renewable resources, such as the wind, water, sun and geothermal heat. Such shifts lead the EPA to project the full 32 percent reduction in CO2 emissions from 2005 levels by 2030. "The nerdier way to say that is that we'll be keeping 870 million tons of carbon dioxide pollution out of our atmosphere," Obama said.

That is significant. But it is also not enough. Here’s what the plan delivers versus what climate scientists say we need:

OVERALL EMISSIONS

Clean Power Plan: Assuming the Clean Power Plan is fully implemented in all 47 affected states, U.S. CO2 emissions just from generating electricity will still add more than 1.7 billion metric tons to the atmosphere each year in 2030—more than the combined emissions of the entire economies of Germany and the U.K. today.

Scientists say: To avoid 2 degree Celsius of warming the world should restrict total emissions of CO2 to no more than one trillion metric tons before 2050 and not exceed atmospheric concentrations of 450 parts per million. There are already nearly 600 billion metric tons of extra CO2 in the atmosphere because of fossil fuel burning, forest clearing and other human activities—a number that increases by roughly 50 billion metric tons per year. These figures suggest that pollution must peak before 2020, a full two years before the plan even comes into effect. Atmospheric CO2 concentrations are already higher than 400 ppm. The cuts included in the plan are a first step but will not be enough to combat climate change.

THE ROLE OF NATURAL GAS

CPP: Natural gas will become the single largest fuel for electricity generation, and gas-fired power plants will run more often—75 percent of the time, up from roughly 50 percent today. Existing nuclear plants do not help states meet emission-reduction targets. Only "uprated" or new nuclear power plants, like those under construction in Georgia and South Carolina, can help ensure compliance. And in case the electricity supply falters, the plan offers exemptions in the form of a so-called "reliability safety valve"—a 90-day period when emissions will not count against a state's reduction goals in the event of emergency, such as extreme weather or a nuclear power plant that must unexpectedly shut down.

Scientists: Natural gas is better than coal—when gas replaces coal as a fuel to generate electricity, CO2 emissions are cut in half—but it still produces CO2 when burned. And when the methane it contains leaks into the atmosphere, it acts as a potent greenhouse gas itself. When natural gas replaces nuclear power, however, CO2 emissions rise, and cheap natural gas can prevent renewable power from being built in the absence of mandates or other policies. Natural gas power plants will still be emitting 771 pounds of CO2 per megawatt-hour of electricity at the end of the Clean Power Plan in 2030, adding yet more to the thickening blanket of atmospheric greenhouse gases and potentially slowing the shift to even cleaner forms of electricity generation, such as renewables or nuclear. "I usually compare natural gas to reduced-fat Oreos," says environmental scientist Steven Davis of the University of California, Irvine. "They may have less calories than the regular ones but if you are morbidly obese, you should be looking for an apple."

THE FATE OF “CLEAN” COAL

CPP: Capturing and storing CO2 pollution from coal-fired power plants is too expensive, says the EPA in the plan, although it is "technically feasible" and "adequately demonstrated." To meet the Clean Power Plan’s emission standard for coal (1,305 lbs/MWh) a new coal-fired power plant would have to capture roughly 20 percent of its CO2—which is why operators are more likely to simply switch to burning natural gas in a combined-cycle turbine than install CO2 capture.

Scientists: All CO2 pollution from coal-fired power plants must be kept out of the atmosphere by 2050 and global pollution must peak around 2020.

CAP AND TRADE

CPP: Individual states will have to craft plans to meet the EPA's new CO2 reduction targets. States that fail to submit a plan by 2018 or submit an inadequate one will be placed into a national cap-and-trade program. Multistate trading regimes, like the Regional Greenhouse Gas Initiative of nine northeastern states, are the preferred option per the EPA. States or generators that exceed mandated reductions can sell those reductions to other states or generators that are struggling to replace coal.

Scientists: Pollution markets can be gamed, especially when subject to a patchwork of rules. Such gaming has been found in international carbon markets, such as the Clean Development Mechanism or the European Union Emissions Trading Scheme as well as regional markets like the Acid Rain Program.

THE NEED TO ACT QUICKLY

CPP: The Clean Energy Incentive Program, a component of the plan, encourages states to make changes early by offering extra emission credits. "We'll reward states that take action sooner instead of later, because time is not on our side here," Obama explained. The EPA will provide pollution allowances or emission-reduction credits for those states that take early action, up to a cap of 272 million metric tons of CO2 among all 47 affected states.

Scientists: It is cheaper to act sooner than later to reduce CO2 pollution. The faster pollution goes down, the less risk of catastrophic climate change.

The Clean Power Plan also cannot encompass other looming challenges from climate change, such as more acidic oceans or tipping points that could lock in the meltdown of ice sheets in Greenland or Antarctica, raising sea levels by many meters this century. These kinds of "important impacts" cannot be monetized, according to the EPA, and therefore suggest that the $20 billion in anticipated climate benefits of the plan are an underestimate. "I don't want to fool you here. This is going to be hard, dealing with climate change," Obama added. "It's exactly the kind of challenge that's big enough to remind us that we're all in this together."

As the plan notes, climate change has become the most pressing environmental problem facing the U.S., especially since "the full warming from any given concentration of CO2 will not be realized for several centuries, underscoring that emission activities today carry with them climate commitments far into the future." This plan is likely the most the U.S. can do given current political realities and therefore is an important step, but that doesn’t mean it’s sufficient.