How long a person can live with emphysema is determined by several factors, including how far their disease has progressed, whether they've stopped the behaviors or ended the exposure to toxic substances that caused the disease, and what treatment they receive.
More Info: Survival rate for any individual is impossible to predict definitively. Studies on survival rates exist but are limited. Physicians use several standards for measuring the stages of emphysema that can help with patient prognosis. The two most widely used are the GOLD emphysema staging system and the BODE emphysema staging system.
The GOLD Emphysema Staging System
This staging system was created by group the Global Initiative for Chronic Pulmonary Lung Disease. The system groups individuals into stages based on airflow obstruction using pulmonary function testing. During the testing, the patient exhales forcefully through a tube that measures airflow capacity in one second. The results are a percentage of forced expiratory volume, or FEV1.
The four stages of emphysema under this system are mild, moderate, severe, and very severe. People with mild emphysema have an FEV1 of 80% or greater. Moderate emphysema patients have an FEV1 between 50%-80%. Severe emphysema patients have an FEV1 between 30%-50%. Very severe emphysema patients have an FEV1 below 30%. 
Life Expectancy: Some studies have suggested that more than half of the patients with an FEV1 below 35% will not survive beyond four years. 
Though this staging system is effective at providing doctors with a standard measurement that can help with treatment recommendations, it cannot accurately predict individual life expectancy.
The BODE Emphysema Staging System
To fill the need to determine a prognosis that incorporates individual's health and habits, some feel that the BODE emphysema staging system does a better job than the GOLD system. The BODE system also measures Body mass index, airflow Obstruction, Dyspnea, and Exercise capacity. The BODE index will measure a low BMI, how far a person can walk in six minutes, and the degree of dyspnea, or shortness of breath. 
Life Expectancy: Based on living more than four years following prognosis as a group these are general observations that will vary greatly between individuals. The higher the risk, such as low BMI and inability to perform daily activities without shortness of breath, the lower the life expectancy.
Mild Emphysema: More than 80% of those categorized in this group live beyond four years.
Moderate Emphysema: 60%-70% of those categorized in this group live beyond four years.
Severe Emphysema: 50% of those categorized in this group live beyond four years.
Most cases of emphysema are caused by smoking or exposure to environmental or occupational airborne pollutants. The best way to halt the progression of the disease and extend life expectancy is to quit smoking or end the exposure to pollutants as quickly as possible. The damage already done is not reversible, but this one single act has the ability to radically slow the progression of the disease if it is still in the primary stages.
Unfortunately, emphysema is currently incurable, and treatment options focus primary on relieving symptoms and improving quality of life. There is some research to indicate that supplemental oxygen can extend the life expectancy of patients with low oxygen levels. Research indicates that while pulmonary rehabilitation does not extend life expectancy in emphysema patients, it does improve quality of remaining life. Avoiding exposure to respiratory illnesses can also significantly increase the life expectancy of emphysema patients.