In 2005, global carbon dioxide (CO2) increased 2.1 parts per million to 378.9 ppm compared to the same period in 2004. That means "that for every one million air molecules there were slightly more than two new CO2 molecules in the atmosphere," the report read.

The Earth's CO2 level during the pre-industrial period was approximately 278 ppm, according to the report.

The increase is largely due to an increase in carbon dioxide emissions from automobile exhaust and coal-fire power plants, as well as nitrous oxide (N20) coming from agricultural industrial activities, it added.

There was a counterbalancing effect from the decrease in methane gas emissions and in emissions of chlorofluorocarbons used widely as refrigerants and in aerosols, the study also found.

On April 27, 10 US states and two cities sued the US government to force it to regulate gases blamed for global climate change, said environmental groups who joined the suit.

The suit demands the Environmental Protection Agency regulate greenhouse gases like carbon dioxide, which the EPA under President George W. Bush has so far avoided, the groups said in a statement.

The EPA does not regulate carbon dioxide, the most plentiful of the greenhouse gases, because the agency, on direction from the White House, does not consider it pollution, the groups said.

While carbon dioxide is not toxic -- humans exhale it in large quantities -- it does contribute to the greenhouse effect, where certain gases in the upper atmosphere allow sunlight in while preventing heat from escaping Earth, not unlike a greenhouse.

The greenhouse effect has always been with us, but scientists say that as cars and power plants release increasing amounts of gases like carbon dioxide, temperatures rise faster and have already begun to disrupt weather patterns.

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US National Oceanic and Atmospheric Administration