Finland introduced a carbon tax (or CO2 tax) based on the carbon content of fossil fuels in January 1990 as an instrument for climate change mitigation.
Source: UNCSD Secretariat (2010) Questionnaire for the Member States on Experiences, Success Factors, Risks and Challenges with Regard to Objective and Themes of UN Conference on Sustainable Development (UNCSD)

"The tax rate evolved from 1.12/t CO2 in 1990 to ?20/t CO2 in 2010. Some deviations existed: natural gas met a reduced rate, and peat was exempted in 2005-2010. In 1994-1996 a combined tax base of carbon+energy content was applied. Since 1997 the carbon tax was imposed only on traffic fuels and heating fuels; electricity was taxed per kWh and the fuels were exempted. CO2 tax revenues in 2010 were approximately 500 million (some 15% of total energy taxes). "