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 world’s 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 year’s 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 CDC’s director for climate change and health who co-authored the reports, told HuffPost by phone last week. “That’s 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.

The Lancet Mean summer warming from 2000 to 2016 area weighted and exposure weighted, relative to the 1986-2008 recent past average.

Disease-carrying insects that thrive in warmer temperatures are also seeing an uptick. Two species of mosquito that carry Dengue ― a tropical virus that causes high fever, headache, vomiting and skin rashes ― increased their ability to spread globally by 9.4 percent and 11.1 percent since the 1950s.

In the U.S., warming temperatures helped West Nile virus become the most common mosquito-borne disease over the past 18 years. Between 1999, when the first U.S. diagnosis was made, and 2015, a total of 43,937 cases were reported, though the number varies significantly year to year. The number of Lyme disease cases in the U.S. has tripled over the past two decades to roughly 300,000 Americans per year as warmer winters expand the area where ticks can survive.

Plant pollen is yet another outdoor menace already made worse by climate change. Americans faced significantly longer exposure to ragweed pollen in 2016 compared to 1990. Ragweed season lasted 17 days longer in Bellevue, Nebraska; three weeks longer in Minneapolis, Minnesota; and exactly 23 additional days in Kansas City, Missouri. Allergy sufferers cost the U.S. $6.2 billion each year, and it’s not limited to hay fever. Indoor molds and fungi also risk becoming a bigger threat.

Temperature increases alone are also causing economic ripples. Since 2000, labor productivity around the world plummeted 5.3 percent in rural areas, where people tend to work outside, including a dramatic 2 percent drop between 2015 and 2016. That equates to more than 920,000 people leaving the workforce, with more than 418,000 in India alone, the report noted.

The total cost of climate-related events hit $129 billion 2016, with 99 percent of those losses in low-income countries with little or no insurance policies. The recent spate of hurricanes that wreaked havoc in the Atlantic ― devastating Puerto Rico, the U.S. Virgin Islands and Barbuda, as well as mainland U.S. cities like Houston and Miami ― offered what scientists described as examples of the kinds of storms that climate change will make more frequent.

But the uptick in weather-related events such as floods and storms may not be statistically significant, according to the report. From 2000 to 2013, the Brussels-based Centre for Research on the Epidemiology of Disasters recorded an average of 341 weather-related disasters per year, up 44 percent from the average between 1994 and 2000. But that’s partly because information systems improved dramatically over the past 35 years, and people have become more concerned with disasters in an age of social media and global trade.

The report concludes that shifting to renewable energy and dramatically reducing greenhouse gas emissions are key to preventing heat- and climate-related maladies. On that front, the report offered some hopeful statistics. Renewable electricity generation capacity increased by 20 percent from 1990 to 2013, exceeding new energy capacity added by fossil fuels for the first time in 2015. In places where renewables replaced fossil fuels ― particularly coal, which worsens air quality and is associated with asthma and other respiratory illnesses ― morbidity and mortality decreased.

The Lancet The U.S. is among the countries that have not taken measures to improve health infrastructure to deal with the influx of climate-related maladies.

But 1.2 billion people still lack access to electricity, and 2.7 billion rely on burning unsustainable or inefficient solid fuels, such as coal. In the U.S., shifting to wind or solar energy from coal resulted in between 3,000 and 12,700 avoided premature deaths from 2007 to 2015, the report found. And programs such as the Regional Greenhouse Gas Initiative ― the largest interstate cap-and-trade market in the country, with nine states across the Northeast and Mid-Atlantic ― offer models to shift states away from fossil fuels even as President Donald Trump pushes them.

“This is really good news because the things we have to do to tackle climate change happen to be good things for health anyway,” Frumkin said. Eating less meat avoids cardiovascular diseases and certain cancers, burning less fossil fuel prevents respiratory illnesses, riding bikes instead of driving cars improves aerobic health and sheds weight, he said, highlighting points made in the inaugural Lancet Countdown report last year.

“If we reduce somewhat the amount of meat in our diets, if we switch off fossil fuels, if we switch from motor vehicles to cycling,” he said. “That has to be our goal.”