This paper discusses the irreversible climate change caused by carbon dioxide emissions. It shows that climate change due to increased carbon dioxide concentrations is largely irreversible for 1,000 years after emissions stop. Even if emissions cease, atmospheric temperatures do not drop significantly for at least 1,000 years. Irreversible impacts include dry-season rainfall reductions in several regions and inexorable sea level rise. Thermal expansion of the warming ocean provides a conservative lower limit to irreversible global average sea level rise of at least 0.4–1.0 m if 21st century CO₂ concentrations exceed 600 ppmv and 0.6–1.9 m for peak CO₂ concentrations exceeding approximately 1,000 ppmv. Additional contributions from glaciers and ice sheets to future sea level rise are uncertain but may equal or exceed several meters over the next millennium or longer. The paper highlights that the atmospheric temperature increases caused by rising carbon dioxide concentrations are not expected to decrease significantly even if carbon emissions were to completely cease. Future carbon dioxide emissions in the 21st century will lead to adverse climate changes on both short and long time scales that would be essentially irreversible. The paper illustrates two aspects of the irreversibly altered world that should be expected: irreversible dry-season rainfall reductions in several regions and inexorable sea level rise. These aspects are among reasons for concern but are not comprehensive; other possible climate impacts include Arctic sea ice retreat, increases in heavy rainfall and flooding, permafrost melt, loss of glaciers and snowpack with attendant changes in water supply, increased intensity of hurricanes, etc. The paper uses models to show how different peak carbon dioxide concentrations that could be attained in the 21st century are expected to lead to substantial and irreversible decreases in dry-season rainfall in a number of already-dry subtropical areas and lower limits to eventual sea level rise of the order of meters, implying unavoidable inundation of many small islands and low-lying coastal areas. The paper also discusses the longevity of an atmospheric CO₂ perturbation, showing that CO₂ equilibrates largely between the atmosphere and the ocean, with approximately 20% of the added tonnes of CO₂ remaining in the atmosphere while approximately 80% are mixed into the ocean. The paper also discusses the irreversible climate change due to carbon dioxide emissions, including the effects on precipitation and sea level rise. The paper concludes that the contribution from the ice sheets could be large in the future, but the dependence upon carbon dioxide levels is extremely uncertain not only over the coming century but also in the millennial time scale.This paper discusses the irreversible climate change caused by carbon dioxide emissions. It shows that climate change due to increased carbon dioxide concentrations is largely irreversible for 1,000 years after emissions stop. Even if emissions cease, atmospheric temperatures do not drop significantly for at least 1,000 years. Irreversible impacts include dry-season rainfall reductions in several regions and inexorable sea level rise. Thermal expansion of the warming ocean provides a conservative lower limit to irreversible global average sea level rise of at least 0.4–1.0 m if 21st century CO₂ concentrations exceed 600 ppmv and 0.6–1.9 m for peak CO₂ concentrations exceeding approximately 1,000 ppmv. Additional contributions from glaciers and ice sheets to future sea level rise are uncertain but may equal or exceed several meters over the next millennium or longer. The paper highlights that the atmospheric temperature increases caused by rising carbon dioxide concentrations are not expected to decrease significantly even if carbon emissions were to completely cease. Future carbon dioxide emissions in the 21st century will lead to adverse climate changes on both short and long time scales that would be essentially irreversible. The paper illustrates two aspects of the irreversibly altered world that should be expected: irreversible dry-season rainfall reductions in several regions and inexorable sea level rise. These aspects are among reasons for concern but are not comprehensive; other possible climate impacts include Arctic sea ice retreat, increases in heavy rainfall and flooding, permafrost melt, loss of glaciers and snowpack with attendant changes in water supply, increased intensity of hurricanes, etc. The paper uses models to show how different peak carbon dioxide concentrations that could be attained in the 21st century are expected to lead to substantial and irreversible decreases in dry-season rainfall in a number of already-dry subtropical areas and lower limits to eventual sea level rise of the order of meters, implying unavoidable inundation of many small islands and low-lying coastal areas. The paper also discusses the longevity of an atmospheric CO₂ perturbation, showing that CO₂ equilibrates largely between the atmosphere and the ocean, with approximately 20% of the added tonnes of CO₂ remaining in the atmosphere while approximately 80% are mixed into the ocean. The paper also discusses the irreversible climate change due to carbon dioxide emissions, including the effects on precipitation and sea level rise. The paper concludes that the contribution from the ice sheets could be large in the future, but the dependence upon carbon dioxide levels is extremely uncertain not only over the coming century but also in the millennial time scale.