The United States and the leaders of the planet’s largest industrialized nations said yesterday at the G-8 summit that the earth has to go green by cutting half of all emissions linked to climate change by the year 2050.

There are big barriers, however, both in the United States and in the developing countries that stand in the way.

In the United States, the climate change bill that has passed in the House falls far short of what scientists say is needed to halt a disaster.

China and India, on the other hand, refused yesterday to commit to specific goals for reducing heat-trapping gases by 2050.

President Obama was the leader most responsible for making climate change a big deal at the G-8 gathering. He engineered the climate change meetings outside the main talks, inviting not just the G-8 countries but nine others, that when taken together, are responsible for 80 percent of the world’s greenhouse gases.

Leaders and activists in the clean environment movement in the U.S. were divided over whether to back the Waxman-Markey climate bill, which passed the House on June 26. The division didn’t happen because anyone thought passage of the bill would not be a historic achievement.

After eight Bush administration years of sabotage, denial, opposition, delay and lies when it came to anything having to do with protecting the environment everyone is celebrating the fact that the United States has finally ordered reductions in the emissions that cause global warming.

Many are unhappy, though, that the bill falls so far short of what is actually needed to do the job.

The Intergovernmental Panel on Climate Change says that world-wide emissions must be cut 25 to 40 percent from 1990 levels by 2020. The cap-and-trade provisions of Waxman-Markey will cut them by only 1 percent by 2020.

There are those who argue that the bill cuts emissions by 17 percent but that is only if you get creative with the statistics, others note. Resulting cuts could only reach 17 percent, they argue, by using as the baseline the higher pollution year of 2005.

Another major weakness of the bill is that it allows pollution permits to be given away rather than sold. This is seen as both subsidizing polluters and delaying the transition to low-carbon energy sources.

Waxman-Markey also cancels the president’s authority under the Clean Air Act to regulate greenhouse emissions. This is seen by most environmentalists as a major step backwards.

Some supporters said the weakening of the measure was the only way to garner the votes needed for passage. Even with the compromises it passed, only 219-212.

Other supporters say the main thing was to get Congress on record in favor of emissions cuts so that the U.S. will have credibility at the important climate change negotiations in Copenhagen next December.

Many environmentalists fear that those very arguments will be made again when the Senate takes up the bill, leading to an even weaker end result.

The other big barrier standing in the way of the goals set by the G-8, is of course, the position in which the developing nations find themselves. Led by India and China, they refused to join the G-8 in adopting emissions targets.

They argue, correctly, that the richest countries have produced the bulk of the pollution responsible for climate change. While they acknowledge that they are producing increasing amounts of these gases they say their ascent from poverty should not be slowed by rules requiring them to repair damage done by rich nations.

As the parties tried to draft an agreement to sign by today the disagreement cancelled the specific goals sought by the United States and Europe.

The proposed agreement called for worldwide emissions to be cut 50 percent by 2050, with industrial countries cutting theirs by 80 percent.

Developing countries refused to agree because they wanted industrial powers to commit to midterm goals in the next decade and to follow through on promises of financial and technological help for poorer countries.

“They’re saying, ‘We just don’t trust you guys,’” said Alden Meyer, of the Union of Concerned Scientists, when he spoke to the press about the talks.

Nevertheless, many feel that gains are being made, even if only that all sides are now committed to the need to find a route to adopting specific reductions.

Also, a separate statement approved by the G-8 adopted the 80 percent emissions cut for industrial nations and agreed to work to prevent world temperature from rising no more than 2 degrees Celsius, or 3.6 degrees Fahrenheit.

The climate meetings were also seen as a positive step because they bought together, ahead of time, many of the participants who will need to cooperate in the coming Copenhagen summit.

Jake Schmidt, the international climate policy director at the Natural Resources Defense Council told the press that, despite the disagreements, it was good to see that countries, including the developing countries, are committed to making reductions, and he said that the 2-degree benchmark would be an important yardstick. He noted that every action put forward from any country will now be measured against whether it helps hold global temperature hikes below 2 degrees.