Climate change is already taking a major toll on public health and threatening to reverse progress made over the past century in combatting infectious diseases, according to one of the worlds oldest and most respected medical journals.

In a landmark new report released Monday evening, The Lancet found that heatwaves over the past two decades were hotter and lasted longer, vector-borne diseases increased as warmer temperatures spread insects, and allergies worsened as unseasonable weather prolonged exposure to pollen.

The journal discussed the potential health effects of climate change in an earlier version of the report, called the Lancet Countdown, but this years 107-page paper is the first to chronicle the existing impacts. As another new feature, the study included a 10-page companion report focused on the United States.

When you go to the doctor and have high blood pressure or a fever, what the doctor does is take a measurement and track it over the next few days, Howard Frumkin, a former special assistant to the CDCs director for climate change and health who co-authored the reports, told HuffPost by phone last week. Thats really what this is on a global scale.

Global warming has become increasingly undeniable over the past decade, with the past two years being the hottest successive years on record, a title 2017 is now on track to surpass.

Heatwaves are the most tangible effect of that temperature rise. According to the report, the average length of individual heatwaves was 0.37 days longer between 2000 and 2016, with an additional 125 million people exposed to annual heatwaves, compared to the period between 1986 and 2008. A record 175 million people were exposed to 627 heatwaves in 2015 alone.

In the U.S., the number of people age 65 and older at risk from extreme heat rose by 14.5 million more than the population of Pennsylvania and the average temperature to which Americans were exposed increased by 1.1 degrees Fahrenheit during that same 16-year period.