1. United States: The US has been the largest historical emitter of CO2, responsible for approximately 25% of global emissions since the late 1800s.

2. China: China has become the largest current emitter of CO2, surpassing the US in recent years. China's rapid economic growth and reliance on coal-fired power plants have contributed to its high emissions.

3. European Union (EU): As a collective entity, the European Union is among the largest historical emitters of CO2. Several European countries, such as Germany, the United Kingdom, and France, have significant industrial histories that have contributed to their carbon emissions.

4. Russia: Russia's historical carbon emissions stem from its substantial use of fossil fuels, particularly natural gas and oil, for energy production and industrial activities.

5. India: India's carbon emissions have been increasing in recent years due to its growing economy and expanding energy demand. India relies on coal-fired power plants for a large portion of its electricity generation.

6. Japan: Japan's emissions are attributed to its highly industrialized economy and dependence on imported fossil fuels for energy.

7. Brazil: Brazil's emissions are primarily due to deforestation, as well as the expansion of agriculture, particularly in the Amazon rainforest region.

8. Indonesia: Indonesia's carbon emissions are largely a result of deforestation, peatland degradation, and the extraction and use of fossil fuels.

9. Iran: Iran's historical emissions are primarily linked to its substantial oil and natural gas reserves and its reliance on fossil fuels for domestic energy consumption and exports.

10. South Africa: South Africa's carbon emissions are mostly attributed to its energy-intensive industries, particularly coal-fired power plants and mining activities.

It's worth noting that while these countries contribute a significant portion of global CO2 emissions, the per-capita emissions may vary significantly among nations. Additionally, some countries have made notable progress in transitioning to renewable energy sources and reducing their carbon footprint in recent years.

Addressing climate change requires global cooperation, as the cumulative impact of emissions from various nations contributes to the overall level of greenhouse gases in the atmosphere. Mitigation efforts, such as reducing fossil fuel dependency, transitioning to renewable energy sources, and enhancing energy efficiency, are crucial for tackling the global climate crisis.