The Climate Change Commitment

Even if atmospheric composition were fixed today, global-mean temperature and sea level rise would continue due to oceanic thermal inertia. These constant-composition (CC) commitments and their uncertainties are quantified. Constant-emissions (CE) commitments are also considered. The CC warming commitment could exceed 1°C. The CE warming commitment is 2° to 6°C by the year 2400. For sea level rise, the CC commitment is 10 centimeters per century (extreme range approximately 1 to 30 centimeters per century) and the CE commitment is 25 centimeters per century (7 to 50 centimeters per century). Avoiding these changes requires, eventually, a reduction in emissions to substantially below present levels. For sea level rise, a substantial long-term commitment may be impossible to avoid. Two climate models indicate that even if stabilization of greenhouse gases at 2000 or 2005 levels were possible, sea level would still rise 30 cm from thermal expansion alone and much more from glacial melting. Two climate models indicate that even if stabilization of greenhouse gases at 2000 or 2005 levels were possible, sea level would still rise 30 cm from thermal expansion alone and much more from glacial melting.