Heatwaves significantly impact male fertility, says huge study

As the world gets hotter, men may have fewer and fewer viable sperm

  • New research on beetles shows that successive exposure to heatwaves reduces male fertility, sometimes to the point of sterility.
  • The research has implications both for how the insect population will sustain itself as well as how human fertility may work on an increasingly hotter Earth.
  • With this and other evidence, it is becoming clear that more common and more extreme heatwaves may be the most dangerous aspect of climate change.

When we hear that climate change causes "extreme weather events," our minds jump to hurricanes ripping palm trees out of the ground or snowstorms burying cars. But one of the most dangerous kind of extreme weather event is much less visible than, say, a tornado tearing the roof of a house. Heatwaves kill more people than all other weather events combined, and they're on the rise.

During the summer of 2003, an estimated 70,000 Europeans died when a deadly heatwave swept through the region. As the globe continues to warm, 150 Americans are projected to die every summer day by the mid-2040s. Aside from directly causing death from heatstroke, dehydration, other heat-related conditions, high heat also weakens cognition. Violent crimes, too, tend to spike on hotter-than-average days.

Now, a new study has uncovered another threat posed by heatwaves. It turns out the prolonged exposure to high heat reduces male fertility, and repeated exposure to successive heatwaves can even cause sterility.

Studying reproductive performance under heatwave conditions

Wikimedia Commons

This image shows the temperature anomalies across Europe during the devastating 2006 heatwave.

The study, recently published in Nature, examined the sperm viability of red flour beetles under heatwave conditions. In a corresponding blog post, study co-author Matthew Gage wrote, "a wealth of research since the start of last century, mainly on warm-blooded mammals (including humans), has shown that environmental or experimental warming by even a few degrees can cause declines in sperm quality and male ability to fertilise."

He points out that most of these studies have been conducted on endothermic, or warm-blooded, animals, but very few studies have been conducted on exothermic, or cold-blooded, animals like insects. Given that the vast majority of animals are ectothermic and that insects serve as food or pollinators for many animals and plants, understanding how climate change affects these creatures is critical to preserving our ecosystem. What's more, studying sperm viability in insects serves as a model for how heatwaves will affect other animals—like humans.

What did they find?

The researchers exposed red flour beetles (like this one) to high-heat conditions to observe their reproductive performance. (Wikimedia Commons)

The researchers exposed their beetles to heatwave-like conditions over the course of five days. Male red flour beetles like temperatures at about 35 degrees Celsius, or 95 degrees Fahrenheit. The experiment exposed them to an environment that was 42 degrees Celsius, or 107.5 degrees Fahrenheit. Depending on where you live, that may sound like an unlikely temperature, but the authors noted that over 90 countries experience heatwaves in that temperature range or higher.

After their extended sauna session, the beetles were given the chance to mate with a female of the species. Compared to male beetles in the control group, the heat-exposed beetles didn't do so well. They produced 75% less sperm, and only one third of their sperm was viable. Overall, the heat-exposed beetles' reproductive performance was cut in half.

But nature is adaptable, right? One might expect the beetles to eventually get over the initial shock of their new, hot environment and perform better. This research showed that, if anything, the opposite is true, at least in the short term. A second exposure to heatwave conditions made the beetles almost completely sterile.

It gets worse; not only did the heat-exposed male beetles do worse than their cooler peers, their male offspring were also less fertile than the offspring of the control beetles. Even when this new generation of beetles was not exposed to heatwave conditions, they had a 25% reduction in mating success. What's more, they lived significantly shorter lives than the control beetles, too.

We've known for a while that certain environmental conditions can affect the health and fertility of offspring, but usually this is in response to irradiation, exposure to toxic chemicals, or stress. When an animal is exposed to an unhealthy environment, the genetic material contained in their sperm becomes damaged, hamstringing the next generation's ability to reproduce. This research suggests that exposure to high heat damages offspring's reproductive ability in the same way.

The environmental impact

While this study looked specifically at beetles, evidence suggests heatwaves will affect mammals in much the same way. Exposing mice to hotter temperatures reduced fertility by 75%, for instance. Overall, "this work reveals that sperm are very sensitive to heat," writes Gage. "Environmentally-relevant experimental heatwaves damage sperm function, leading to reduced fertility and a decline in offspring performance."

If this effect is widespread enough, it could throw a serious monkey wrench into the inner workings of our ecosystem. The importance of insects in the diets of large animals cannot be overstated. As the globe continues to warm, insect populations are crashing. One study in Germany found that the local insect population had dropped by 78% in just 24 years, which appears to be part of a global trend. While it can't be said that this is entirely due to increasingly common and extreme heatwaves, this research suggests that they may play a major role.



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Maps show how CNN lost America to Fox News

Is this proof of a dramatic shift?

Strange Maps
  • Map details dramatic shift from CNN to Fox News over 10-year period
  • Does it show the triumph of "fake news" — or, rather, its defeat?
  • A closer look at the map's legend allows for more complex analyses

Dramatic and misleading

Image: Reddit / SICResearch

The situation today: CNN pushed back to the edges of the country.

Over the course of no more than a decade, America has radically switched favorites when it comes to cable news networks. As this sequence of maps showing TMAs (Television Market Areas) suggests, CNN is out, Fox News is in.

The maps are certainly dramatic, but also a bit misleading. They nevertheless provide some insight into the state of journalism and the public's attitudes toward the press in the US.

Let's zoom in:

  • It's 2008, on the eve of the Obama Era. CNN (blue) dominates the cable news landscape across America. Fox News (red) is an upstart (°1996) with a few regional bastions in the South.
  • By 2010, Fox News has broken out of its southern heartland, colonizing markets in the Midwest and the Northwest — and even northern Maine and southern Alaska.
  • Two years later, Fox News has lost those two outliers, but has filled up in the middle: it now boasts two large, contiguous blocks in the southeast and northwest, almost touching.
  • In 2014, Fox News seems past its prime. The northwestern block has shrunk, the southeastern one has fragmented.
  • Energised by Trump's 2016 presidential campaign, Fox News is back with a vengeance. Not only have Maine and Alaska gone from entirely blue to entirely red, so has most of the rest of the U.S. Fox News has plugged the Nebraska Gap: it's no longer possible to walk from coast to coast across CNN territory.
  • By 2018, the fortunes from a decade earlier have almost reversed. Fox News rules the roost. CNN clings on to the Pacific Coast, New Mexico, Minnesota and parts of the Northeast — plus a smattering of metropolitan areas in the South and Midwest.

"Frightening map"

Image source: Reddit / SICResearch

This sequence of maps, showing America turning from blue to red, elicited strong reactions on the Reddit forum where it was published last week. For some, the takeover by Fox News illustrates the demise of all that's good and fair about news journalism. Among the comments?

  • "The end is near."
  • "The idiocracy grows."
  • "(It's) like a spreading disease."
  • "One of the more frightening maps I've seen."
For others, the maps are less about the rise of Fox News, and more about CNN's self-inflicted downward spiral:
  • "LOL that's what happens when you're fake news!"
  • "CNN went down the toilet on quality."
  • "A Minecraft YouTuber could beat CNN's numbers."
  • "CNN has become more like a high-school production of a news show."

Not a few find fault with both channels, even if not always to the same degree:

  • "That anybody considers either of those networks good news sources is troubling."
  • "Both leave you understanding less rather than more."
  • "This is what happens when you spout bullsh-- for two years straight. People find an alternative — even if it's just different bullsh--."
  • "CNN is sh-- but it's nowhere close to the outright bullsh-- and baseless propaganda Fox News spews."

"Old people learning to Google"

Image: Google Trends

CNN vs. Fox News search terms (200!-2018)

But what do the maps actually show? Created by SICResearch, they do show a huge evolution, but not of both cable news networks' audience size (i.e. Nielsen ratings). The dramatic shift is one in Google search trends. In other words, it shows how often people type in "CNN" or "Fox News" when surfing the web. And that does not necessarily reflect the relative popularity of both networks. As some commenters suggest:

  • "I can't remember the last time that I've searched for a news channel on Google. Is it really that difficult for people to type 'cnn.com'?"
  • "More than anything else, these maps show smart phone proliferation (among older people) more than anything else."
  • "This is a map of how old people and rural areas have learned to use Google in the last decade."
  • "This is basically a map of people who don't understand how the internet works, and it's no surprise that it leans conservative."

A visual image as strong as this map sequence looks designed to elicit a vehement response — and its lack of context offers viewers little new information to challenge their preconceptions. Like the news itself, cartography pretends to be objective, but always has an agenda of its own, even if just by the selection of its topics.

The trick is not to despair of maps (or news) but to get a good sense of the parameters that are in play. And, as is often the case (with both maps and news), what's left out is at least as significant as what's actually shown.

One important point: while Fox News is the sole major purveyor of news and opinion with a conservative/right-wing slant, CNN has more competition in the center/left part of the spectrum, notably from MSNBC.

Another: the average age of cable news viewers — whether they watch CNN or Fox News — is in the mid-60s. As a result of a shift in generational habits, TV viewing is down across the board. Younger people are more comfortable with a "cafeteria" approach to their news menu, selecting alternative and online sources for their information.

It should also be noted, however, that Fox News, according to Harvard's Nieman Lab, dominates Facebook when it comes to engagement among news outlets.

CNN, Fox and MSNBC

Image: Google Trends

CNN vs. Fox (without the 'News'; may include searches for actual foxes). See MSNBC (in yellow) for comparison

For the record, here are the Nielsen ratings for average daily viewer total for the three main cable news networks, for 2018 (compared to 2017):

  • Fox News: 1,425,000 (-5%)
  • MSNBC: 994,000 (+12%)
  • CNN: 706,000 (-9%)

And according to this recent overview, the top 50 of the most popular websites in the U.S. includes cnn.com in 28th place, and foxnews.com in... 27th place.

The top 5, in descending order, consists of google.com, youtube.com, facebook.com, amazon.com and yahoo.com — the latter being the highest-placed website in the News and Media category.
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