Life expectancy at birth is a statistical measure, internally consistent and useful for comparisons across time. Insofar as it has a real meaning it is the average expected life span of a person born now if medical technology going forward exactly repeated past availability and cost over the life spans of people presently at the end of life. Obviously that won't happen, but nonetheless this is still a useful way to keep track of progress. Since it is a measure from birth it is greatly influenced by childhood mortality and mortality due to infectious disease, and indeed much of the gains in life expectancy over the past two centuries have been due to reductions in causes of death while young. That is no longer the case now in most parts of the world, however, and ongoing gains have more to do with reduction of mortality in later years.
This study confirms other work that shows the ballpark growth in life expectancy at birth is something like one year with every four calendar years. Adult life expectancy is also climbing, but more slowly - perhaps one year each decade. This present pace will change as the research community starts to deliberately target aging for treatment, which has not previously been the case. Past gains in life expectancy at age 30 or 60 due to improvements in medicine have been somewhat incidental, side-effects rather than deliberately obtained results.
Global life expectancy for both sexes increased from 65.3 years in 1990, to 71.5 years in 2013, while the number of deaths [per year] increased from 47.5 million to 54.9 million over the same interval. Global progress masked variation by age and sex: for children, average absolute differences between countries decreased but relative differences increased. For women aged 25-39 years and older than 75 years and for men aged 20-49 years and 65 years and older, both absolute and relative differences increased. Decomposition of global and regional life expectancy showed the prominent role of reductions in age-standardised death rates for cardiovascular diseases and cancers in high-income regions, and reductions in child deaths from diarrhoea, lower respiratory infections, and neonatal causes in low-income regions.
For most countries, the general pattern of reductions in age-sex specific mortality has been associated with a progressive shift towards a larger share of the remaining deaths caused by non-communicable disease and injuries. For most communicable causes of death both numbers of deaths and age-standardised death rates fell whereas for most non-communicable causes, demographic shifts have increased numbers of deaths but decreased age-standardised death rates. Global deaths from injury increased by 10.7%, from 4.3 million deaths in 1990 to 4.8 million in 2013; but age-standardised rates declined over the same period by 21%. For some causes of more than 100,000 deaths per year in 2013, age-standardised death rates increased between 1990 and 2013, including HIV/AIDS, pancreatic cancer, atrial fibrillation and flutter, drug use disorders, diabetes, chronic kidney disease, and sickle-cell anaemias.