Back in 2005, the U.S. Energy Information Administration projected that, under current policies, U.S. energy-related carbon dioxide emissions would increase nearly 18 percent by 2015.

They did not.

In fact, emissions fell – by more than 12 percent. So we were off by 30 percent.

As Yogi Berra may have said: It’s tough to make predictions, especially about the future. We didn’t know then the impact a variety of market and policy factors would have on our energy mix. And we don’t know now all of the factors that could help us meet, or exceed, our Paris Agreement pledge – to reduce our net emissions 26-28 percent below 2005 levels by 2025.

U.S. emissions have fallen over the last 10 years due to factors that include:

• Growth in renewable energy
• Level electricity demand
• Improved vehicle efficiency
• A shift in electricity generation from coal to natural gas.

An unanticipated abundance of cheap natural gas has transformed the U.S. electricity mix. Coal-fired generation has fallen from 50 to 33 percent of the mix, while less carbon-intensive, natural gas-fired generation has risen from 19 to 33 percent.

The last 10 years also included a major economic downturn, which in 2009 drove electricity sales below 2005 levels. Despite a return to positive economic growth in the following year that continues through today, electricity sales have remained flat. Declines in manufacturing; improvements in energy efficiency, including in buildings, lighting, and appliances; warmer winters; and increased use of on-site generation like rooftop solar panels are the likely drivers.

What will happen in the next 10 years?

Certainly, the electric power sector will continue to decarbonize. It is not unreasonable to assume that natural gas will play an even larger role, while coal will play a substantial albeit diminishing role in the electricity mix.

Here are some other factors that are hard to quantify now, but could affect how quickly we transition to a clean energy future:

More zero-emission electricity

Increased clean and renewable electricity production, spurred by the Environmental Protection Agency’s Clean Power Plan and congressional tax credit extensions for wind and solar, could reduce renewable power costs, which have already been dropping. In other words, economies of scale could lead to higher deployments and lower emissions than currently forecast.

Wind and solar generation have grown nearly twelve-fold since 2005, nearly eight times greater than what was expected back then. In the 2016 Annual Energy Outlook, wind and solar generation are projected to increase 2.5 times by 2025. Historical precedent would tend to suggest that this is a highly conservative estimate.

However, sustained low prices in wholesale power markets from low natural gas prices and a proliferation of renewable electricity sources could harm another zero-emission source: nuclear. In particular, we could see natural gas continue to replace zero-emission merchant nuclear plants, moving us in the wrong direction, unless remedies are implemented. Also, low wholesale prices would tend to discourage new renewable generation.

More zero-emission vehicles

Electric vehicles (EVs) make up less than 1 percent of new U.S. car sales. But as their prices drop and range expands, the adoption rate could accelerate over the next 10 years, spurring important reductions from what is now the largest emitting sector. In one sign of growing demand, more than 400,000 people have put down a deposit for a Tesla Model 3 EV that won’t even be on the market until 2018.

Advances in battery storage could drive the transformation of the transportation sector and would provide obvious benefits to the electric power sector as well.

Meanwhile, automakers are exploring alternative fuels: natural gas, hydrogen fuel cells, and biofuels. And more than a dozen states and nations have formed a Zero-Emission Vehicle (ZEV) Alliance to encourage ZEV infrastructure and adoption.

City action

Action by cities, the magnitude of which is not easily captured by national macroeconomic models, could lead to greater than anticipated emission reductions. Starting with the groundbreaking Mayors Climate Protection Agreement in 2005, initiatives are evolving to connect cities with each other to exchange knowledge and achieve economies of scale for new technologies.

More cities are exploring ways to generate additional reductions by 2025. These include: more energy-efficient buildings; better tracking of electricity and water use, innovative financing for more efficient generation, appliances and equipment; and improved public transportation and promotion of electric vehicles.

Business action

Last, but not least, steps taken by companies beyond regulatory requirements could produce greater emission reductions than we can foresee. Companies are investing in clean energy projects, reducing emissions throughout the supply chain, establishing internal carbon pricing, and helping customers reduce their carbon footprint. More than 150 companies have signed the American Business Act on Climate Pledge.

C2ES and The U.S. Conference of Mayors are teaming up to encourage city and business leaders to work together to reduce greenhouse gas emissions. Imagine how effective we can be when we coordinate climate action.

A 2015 UNEP report suggests that beyond each countries’ individual commitments to the Paris Agreement, actions by sub-national actors across the globe can result in net additional contributions of 0.75 to 2 billion metric tons of carbon dioxide emissions in 2020.

The United States has significantly reduced its greenhouse gases over the past decade, and has put in place policies ensuring continued reductions in the years ahead. With so many resources and tools at our disposal, it is clear that we can meet or exceed our climate goal. The only uncertainty is how we will do it.

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Event: Innovation to Power the Nation

Technology, policy, and business experts discuss how innovative technology and policy can help us reach our climate goals at Innovation to Power the Nation (and World): Reinventing Our Climate Future at 1 p.m. ET on Wednesday, June 29. Watch the livestream.

Speakers include Patent and Trademark Office Director Michelle K. Lee; C2ES President Bob Perciasepe; Dr. Kristina Johnson, CEO of Cube Hydro Partners; Nate Hurst, Chief Sustainability & Social Impact Officer at HP; and Dr. B. Jayant Baliga, inventor and director of the Power Semiconductor Research Center at North Carolina State University.