As other countries struggle to cut greenhouse gas emissions, two ex-Soviet industrial powerhouses have found themselves heirs to an unlikely windfall.

Russia and Ukraine head into the Copenhagen summit with credits for billions of tons of carbon dioxide they no longer belch, thanks to the collapse of the Soviet industrial machine that gave them favorable terms under the 1997 Kyoto Protocol.

The situation allows the two countries not only to pollute more but also sell carbon credits to other countries for millions of dollars.

Now environmentalists and some European countries are urging Moscow and Kiev to give up those credits and strengthen efforts to slash global carbon production. Both countries say they won't do so without a fight.

President Dmitry Medvedev said in a video blog posted this week that Russia is committed to limiting greenhouse gases by 2020 by expanding the use of nuclear power and promoting energy efficiency. "This is a question of existence itself," he said.

But he also pointed out that Russia's carbon emissions today are about 34 percent lower than they were in 1990. He said the Kremlin plans to allow emissions to grow over the next decade, although by 2010 they will still be 25 percent below 1990.

Alexander Bedritsky, a Kremlin adviser, told reporters last week that European nations are calling on Russia to slash its output of carbon dioxide at a time when the European Union hasn't been able to meet its own goals under Kyoto. He said the EU's emissions have risen steadily since 1990, unlike Russia's.

"They take on certain commitments, don't fulfill them and then go out there shouting about new and more ambitious ones," he said.

In 1990 the antiquated Soviet military-industrial complex was still churning along at full speed as smokestacks belched hot gases and soot across the U.S.S.R. But the Soviet Union collapsed a year later and by the mid-1990s many of these factories were shuttered and rusting.

Under the Kyoto treaty, emissions cuts are measured against 1990 levels, meaning that on paper, former Soviet states have made steep cuts over the past 20 years. This gave them billions of tons of carbon allowances that they could sell on to other countries, mainly in Europe, which needed them to meet their own commitments under Kyoto.

Many Kyoto participants have complained of the alleged injustice of this provision. But a key priority for both Russia and Ukraine at the current climate talks in Copenhagen is to hold on to these credits after Kyoto expires in 2012.