Explanation:

1. Correct: Carbon credits in voluntary markets are often more expensive than those in compliance markets. This is because entities in voluntary markets often seek credits that offer additional benefits, like supporting biodiversity or social upliftment, which can command higher prices.
2. Incorrect: Not all carbon offset projects directly remove carbon dioxide from the atmosphere. Some might prevent further emissions (e.g., renewable energy projects) or capture and store carbon (e.g., reforestation). Direct removal is only one method among several.
3. Incorrect: The Clean Development Mechanism (CDM) is not an American initiative. It is one of the Kyoto Protocol's flexible mechanisms, an international treaty aimed at combatting climate change. The CDM allows developed nations to invest in emission-reducing projects in developing countries as a way to meet their own emission-reduction targets.
4. Incorrect: Carbon markets do not only operate on a national level. They have significant international implications, with credits being traded across borders. International mechanisms like the CDM are clear examples of the global nature of carbon markets

?So, only 1 out of the 4 statements is correct.