31 January 2013, 13:57 BST
Although many people criticize the ability of corporations or countries to "offset" their emissions by paying for clean energy projects in developing countries, there are now 6000 such projects around the world.
Under the Kyoto Protocol's Clean Development Mechanism (CDM), emission-reduction projects in developing countries - such as conserving high priority forests or developing clean energy projects - apply for certified emission reduction credits, each equivalent to one ton of carbon.
If countries can't meet their carbon reduction targets by cutting emissions alone, they can offset part of that by investing in these projects.
"This mechanism stimulates sustainable development and emission reductions, while giving industrialized countries some flexibility in how they meet their emission reduction limitation targets," says the United Nations, which governs the program.
A 21 megawatt (MW) wind farm in Vietnam is the 6000th project, which displaces fossil-fuel-generated power and reduces emissions by 32,000 ton a year.
In the past 10 years, CDM projects have delivered 110,000 MW of renewable energy capacity, roughly equivalent to Africa's total power generation capacity.
Registered CDM projects are in 83 developing countries and range from replacing inefficient wood stoves to solar projects and increased industrial efficiency.
One example is a forestry project in Ethiopia, which is alleviating poverty as well as cutting emissions and building resilience to climate change. More than 2,700 hectares of degraded land has been restored where just about all the trees had been cleared.
In December, at the international climate summit Qatar, governments agreed to renew the Kyoto Protocol until 2020, which includes market-based tools like the Clean Development Mechanism.
Research shows that the CDM has spurred $215 billion in investments, but low prices for certified emission reduction credits threaten the program. The value of credits is down over 90% in the past year because of weak demand.