The Paris Agreement on Climate Change comes into effect today, November 4. Auspiciously for climate warriors, that is just three days before the next United Nations climate change conference opens in Marrakech, Morocco.

The Marrakech negotiations, held in conjunction with the Conference of the Parties to the U.N. Framework Convention on Climate Change (COP-22), will be the first meeting of the parties to the Paris Agreement, known in UN-speak as CMA1. Countries that have not yet joined the Paris Agreement can attend and participate in the CMA sessions, but only as observers. They do not have decision-making authority.

The goal of the Paris Agreement, adopted last December, is to hold "the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels." Current global temperature hovers around 1°C above the pre-industrial average.

Each party to the agreement has submitted its nationally determined contributions (NDCs) to the United Nations explaining how they plan to help keep the climate from growing excessively warm. The U.S. NDC involves reducing economy-wide greenhouse gas emissions by 26 to 28 percent below its 2005 level in 2025 and making best efforts to reduce emissions by 28 percent.

The really interesting feature of the Paris Agreement is that the nationally determined contribution plans filed by each of its signatories are voluntary. Its legally binding sections are chiefly mandates that countries provide and periodically update the levels of greenhouse gases they are emitting. This reporting requirement is not much different than out obligations under the previously ratified U.N. Framework Convention on Climate Change. Basically, countries are supposed to tell the others how they are doing.

A critical part of President Obama's climate change strategy is the Environmental Protection Agency's Clean Power Plan (CPP), which would require carbon dioxide emissions from electric power generation to fall by 30 percent below 2005 levels in 2030. The U.S. Supreme Court stayed its implementation and a number of states have filed federal lawsuits to stop the program. Meanwhile, thanks largely to massive new supplies of cheap shale gas liberated by fracking, the U.S. has produced the lowest carbon dioxide emissions for the first six months of the year since 1991. (Lots of electric power generators have switched from coal to natural gas, which emits only about half as much carbon dioxide.) As a consequence, greenhouse gas emissions in 2014 were 9 percent below 2005 levels. (In 2010, President Obama pledged to cut U.S. emissions by 17 percent below 2005 levels in 2020. Only four years to go!)

So how likely is the U.S. to fulfill Obama's greenhouse-gas pledges? Keeping firmly in mind that energy modeling is largely an exercise in policy fiction and wishful thinking, let's take a look at some projections of future U.S. energy use and greenhouse emissions.

A new study by the ICF International consultancy, commissioned by the American Petroleum Institute, modeled how the power sector would evolve if market forces determined the fuel generation mix and new capacity additions—as opposed to government-mandated choices under the Clean Power Plan. The analysts found that carbon dioxide emissions from the power sector would drop by 30 percent from 2005 levels in 2030—deeper cuts than those that would result from CPP regulations. This outcome, however, depends on high-end estimates of how much recoverable shale gas there is. In either the market or mandate scenarios, coal continues to fade as a source of energy.

Another analysis—by researchers at the Lawrence Berkeley National Laboratory, published in the October issue of Nature Climate Change—calculated that current policies being pursued by the Obama administration will fall far short of their stated emissions reduction goals. They estimate that emissions would drop by only about 9 percent below their 2005 levels in 2025.

A new report by the economics consultancy Lux Research looks at what might happen to greenhouse emissions were Donald Trump to be president for two terms. Lux Research analysts conclude that the downward trend in U.S. carbon dioxide emissions would reverse and actually be 16 percent higher than they would be if Clinton were president.

Speaking of Trump, the Republican nominee has declared that if elected he will cancel U.S. participation in the Paris Agreement. Earlier this week, China's top climate change negotiator Xie Zhenhua was asked about Trump's promise. "If they resist this trend, I don't think they'll win the support of their people, and their country's economic and social progress will also be affected," Xie said. "I believe a wise political leader should take policy stances that conform with global trends."

Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions, claimed this week in Reuters that "Entry into force only goes one way. It can't be reversed." Is that so?

Once the Paris Agreement is in force, signatories are supposed to wait three years before they can file a notification that they are withdrawing from it. They must then wait another year before the withdrawal takes effect. In other words, the Paris Agreement would apply to the U.S. for the first full term of a Trump presidency. It seems unlikely that Trump would follow this path.

Another option would be for Trump to withdraw from the UNFCCC entirely, a process that would take only one year. Under the terms of the UNFCCC, "Any Party that withdraws from the Convention shall be considered as also having withdrawn from any protocol to which it is a Party." Good-bye, Paris Agreement.

Finally, a Trump administration could simply ignore the promises made by the Obama administration and dismantle any domestic regulations aimed at cutting greenhouse gas emissions. After all, the targets under the Paris Agreement are voluntary.

Will any of that affect next Tuesday's outcome? Most Americans tell pollsters that they are worried about climate change. Nevertheless, the issue was essentially absent from the presidential debates, and concern about pollution and the environment is at rock bottom on polls asking voters to identify the country's most important problems. Upshot: The few one-issue climate voters will not sway this election one way or the other.