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Climate change reduces male fertility

November 13, 2018

Researchers are honing in on a little-studied but significant consequence of climate change: male infertility. Could this potential cause of extinction and biodiversity loss also threaten the human species?

Image: picture-alliance/dpa/LEHTIKUVA/M. Kainulainen

Men have long understood the dangers of exposing their reproductive glands to excessive heat. More than a decade ago, celebrity chef Gordon Ramsey publicly admitted that all that time near hot stoves ultimately caused him fertility loss and a low sperm count. "My balls were burning," he said, with typical bluntness.  

From sitting too long with a laptop, to boiling saunas and hot cellphones in tight jean pockets, burning issues around the midriff have become a pressing fertility enemy for modern men.

Recent research is implicating rising heat due to climate change as an extinction threat for certain species — so what about our own?

Read moreNo help for the infertile in Africa

The world warms, births decline

While day-to-day thermal threats to male reproductivity can be combated with common sense, what happens when there is little escape from a world that is warming due to climate change?

Two young men cooling off with a fan at a window in Milan
Sweltering — and less fertile?Image: picture-alliance/ROPI/Piaggesi/Fotogramma

This past July, Alan Barreca, an environmental economist from the University of California in Los Angeles released a study showing that "temperature shocks" linked to climate change were reducing birth rates, despite increased sexual activity in summer months.

Derived from 80 years of birth and weather data out of the United States, the study confirmed a higher number of babies being born in August and September (nine months after the depths of winter), while fewer babies were conceived in summer due to higher temperatures.

The researchers warned that the higher frequency and severity of heat waves — which is expected as climate change carries on — will hasten this decline in fertility.

"Climate change projections show dramatic increases in hot weather," Barreca told DW. "This increase in hot weather will harm our reproductive health in the future."

Damaging the seed of life

This human dimension to the problem of decreased fertility in a warming world is just one part of a significantly more far-reaching problem.

A study by researchers at the University of East Anglia,published today in Nature Communications, shows "clear evidence" that heat-wave stress reduces "sperm number and viability" in insects, those most ubiquitous of living creatures.

Male and female symbols made of beetles
Climate change is affecting reproduction among insectsImage: M. Gage/M. Taylor

"In warm-blooded systems, heat is not a good thing for male fertility," Matthew Gage, a professor of evolutionary ecology at the University of East Anglia and lead researcher on the study, told DW.

However, humans and other warm-blooded animals are able to regulate their internal reproductive systems, meaning that their sperm is somewhat protected under heat stress, Gage explained.

Yet as heat waves become more frequent, few have looked at "cold-blooded organisms [such as insects] that comprise the majority of biodiversity on Earth," he added.

Read more: Beetle mania: The planet's most successful creatures?

After exposing beetles that thrive in tropical environments to heat stress, the research not only confirmed a hunch about fertility loss in the planet's most common species, but also noted "male reproductive damage" and "transgenerational impacts" that could help clarify increasing species extinction rates.

It's the first such study to reveal a link between heat-wave stress and long-lasting genetic or DNA damage — and the potential for heat stress to create permanently sterile males.

Read moreBiodiversity collapse imminent in world's tropics, study says

Explaining biodiversity loss

"Could this be one of the reasons why populations decline and go extinct under climate change?" Gage asked. "Obviously, if you're not very good at reproducing, that's not going to help your population viability," he pointed out.

A heat wave will ultimately pass and a creature may survive it — but, added Gage, "this can't undo the problem of damaged sperm."

Why do we need diversity of species?

Upon examining insects that had suffered a heat wave, "their offspring showed shortened lifespan and lower reproductive fitness," said Gage, pointing out that this represents a transgenerational defect.

The significance of this linkage is potentially devastating for biodiversity loss on a warming planet.

Read moreScientists race to name unknown species before biodiversity disappears

That could be taken a step further as all living organisms ultimately depend on each other for survival. For instance, without pollinating insects, the human diet would be far poorer. 

Read more'We cannot survive without insects'

Taking the heat

A 2017 review of studies into rapidly declining sperm counts in men went as far as to warn of human extinction if the trend of a recorded 50 to 60 percent drop in sperm count in males from North America, Europe and Australia from 1973 to 2011 continues.

The study cited "multiple environmental and lifestyle influences" that might explain the declining sperm count. These included prenatal endocrine disruption caused by exposure to chemicals, or maternal smoking — while exposure to pesticides could be a prime culprit in adult life. 

Yet conclusive evidence linking declining fertility to any specific environmental problem is lacking.

New research on the correlation between increased male infertility and climate change could therefore prove to be especially instructive. Moreover, if this link is contributing to broader biodiversity loss, the consequences will again be devastating for all life.

This is why Gage and his team are starting to trace the link between heat stress and loss of male fertility — and transgeneration DNA defects — in a host of other insects and cold-blooded animals, including fish that spawn in very cold waters.

"It adds up to a pretty hard time for populations that are already suffering stress from all sorts of other things like habitat loss, or chemicals being put into the system," noted Gage of the latest death knell for threatened species across the planet.

If further research proves that a warming world is impairing the seed of life, the revelation could be the ultimate inspiration to double down on fighting climate change.

Read moreTo save species, limit global warming

Stuart Braun | DW Reporter
Stuart Braun Berlin-based journalist with a focus on climate and culture.
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