The organizing committee of the Sochi Olympics has claimed that the carbon dioxide emissions associated with running the games have been offset by reducing emissions elsewhere—making these the first ever carbon-neutral Olympic games.

But some experts say that not all of the emissions have been accounted for, and that the net environmental impact of the games may be worse than for previous ones. “Without a doubt, the Sochi Olympics are not carbon-neutral games,” says Allen Hershkowitz, who directs the sports greening project at the Natural Resources Defense Council.

The Sochi Olympics are emitting a lot of carbon dioxide. According to official estimates, putting on the Olympics directly emits 360,000 tons of carbon dioxide. Travel for spectators and judges add another 160,000 tons. Altogether, that’s the equivalent of providing electricity from a coal plant—the most carbon-intensive source of power—to about two million people for the duration of the games.

These estimates account for the fact that the organizing committee made efforts to lower emissions by choosing efficient technology for heating and lighting Olympic venues. It also installed solar panels on some buildings to reduce power plant emissions.

The Sochi organizers partnered with Dow Chemical to find ways to offset carbon dioxide emissions, and turned to the sustainability consultancy ERM to verify them. Dow says it has offset more than 500,000 tons of carbon dioxide by installing energy efficiency technologies and improving manufacturing practices in Russia (Dow purchased carbon credits for the balance of offsets). For example, working with about 50 contractors, Dow introduced insulating foam into about 20,000 homes. Dow reformulated the foam to withstand the extreme cold found in much of Russia, and changed the way it’s made in Russia to use less potent greenhouse gases.

Yet Russia’s preparation for the Olympics, which cost about $51 billion, involved massive new construction. The Sochi carbon emissions estimates don’t include emissions from construction activities, says Irina Komissarova, a project manager for environmental projects for the Sochi 2014 Olympic Organizing Committee. (In contrast, this video on Dow’s website makes it sound as if contruction emissions were included.)

When you count the emissions associated with the rapid construction of Olympic venues, housing, and new roads and railways, the Sochi Olympics might be worse in terms of net emissions than previous ones, says Robert Engelman, president of the Worldwatch Institute.

In addition to the direct emissions from manufacturing building materials and operating equipment, construction can also cause indirect emissions. Cutting down trees and disturbing soil can release stored carbon dioxide into the atmosphere. Fast-paced construction damaged 30 square kilometers of pristine forest in a national park in the Sochi area, according to the World Wildlife Fund in Russia. (Russian legislators passed a law to allow the cutting down of previously protected rare trees during Olympic construction.)

Hershkowitz, who has overseen carbon offset programs for events such as the Oscars, says that the sheer size of the Olympics means that it’s impossible to account for everything—for example, the energy used to grow food and make paper programs. For some building materials, such as plastic pipes, the total emissions of making and disposing them aren’t even known, and would take years of study to determine. “There’s no way in the world you can document all of the carbon emissions,” he says.

While Engelman says the games aren’t carbon neutral, he praises the organizing committee for promoting energy efficiency technologies, which could have a positive legacy beyond the games (see “Putting Building Science into Practice”).

Michael Mazor, a building scientist in Dow’s Energy and Climate Change business, hopes the Olympics have opened a new market for energy efficiency technology that could lead to more carbon emission reductions in the future. “The 20,000 [homes we upgraded] didn’t put a dent in the market,” he says. “We hope to do two million, or 20 million.”

Some environmentalists in Russia are skeptical that energy efficiency technology will take off. “The potential of energy efficiency is huge,” says Alexander Tsygankov, the energy unit head of Greenpeace Russia. “But there is no real progress in it.”