climate change sex drive birth rates orig mg mss_00010706.jpg
climate change sex drive birth rates orig mg mss_00010706.jpg
Now playing
01:21
Study: Climate change is killing our sex drive
Commanding General District of Columbia National Guard Major General William J. Walker testifies before the Senate Homeland Security and Governmental Affairs/Rules and Administration hearing to examine the January 6, 2021 attack on the US Capitol on Capitol Hill on March 3, 2021 in Washington, DC. (Photo by Greg Nash / POOL / AFP) (Photo by GREG NASH/POOL/AFP via Getty Images)
PHOTO: GREG NASH/POOL/AFP via Getty Images
Commanding General District of Columbia National Guard Major General William J. Walker testifies before the Senate Homeland Security and Governmental Affairs/Rules and Administration hearing to examine the January 6, 2021 attack on the US Capitol on Capitol Hill on March 3, 2021 in Washington, DC. (Photo by Greg Nash / POOL / AFP) (Photo by GREG NASH/POOL/AFP via Getty Images)
Now playing
03:01
DC National Guard commander: 'Unusual' Pentagon restrictions slowed response to Capitol riot
Supporters of President Donald Trump hold up their phones with messages referring to the QAnon conspiracy theory at a campaign rally at Las Vegas Convention Center on February 21, 2020 in Las Vegas, Nevada.
PHOTO: Mario Tama/Getty Images
Supporters of President Donald Trump hold up their phones with messages referring to the QAnon conspiracy theory at a campaign rally at Las Vegas Convention Center on February 21, 2020 in Las Vegas, Nevada.
Now playing
03:00
Hear why QAnon supporters believe Trump will be president on March 4th
FBI Director Christopher Wray testifies before the Senate Judiciary Committee on the January 6th insurrection, in the Hart Senate Office Building on Capitol Hill in Washington, DC on March 2, 2021. (Photo by MANDEL NGAN / POOL / AFP) (Photo by MANDEL NGAN/POOL/AFP via Getty Images)
PHOTO: MANDEL NGAN/POOL/AFP via Getty Images
FBI Director Christopher Wray testifies before the Senate Judiciary Committee on the January 6th insurrection, in the Hart Senate Office Building on Capitol Hill in Washington, DC on March 2, 2021. (Photo by MANDEL NGAN / POOL / AFP) (Photo by MANDEL NGAN/POOL/AFP via Getty Images)
Now playing
02:55
Watch FBI director debunk conspiracy theories pushed by Trump supporters
WASHINGTON, DC - FEBRUARY 10: Neera Tanden, nominee for Director of the Office of Management and Budget (OMB), testifies at her confirmation hearing before the Senate Budget Committee on February 10, 2021 at the U.S. Capitol in Washington, DC. Tanden helped found the Center for American Progress, a policy research and advocacy organization and has held senior advisory positions in Democratic politics since the Clinton administration. (Photo by Anna Moneymaker-Pool/Getty Images)
PHOTO: Anna Moneymaker-Pool/Getty Images
WASHINGTON, DC - FEBRUARY 10: Neera Tanden, nominee for Director of the Office of Management and Budget (OMB), testifies at her confirmation hearing before the Senate Budget Committee on February 10, 2021 at the U.S. Capitol in Washington, DC. Tanden helped found the Center for American Progress, a policy research and advocacy organization and has held senior advisory positions in Democratic politics since the Clinton administration. (Photo by Anna Moneymaker-Pool/Getty Images)
Now playing
01:33
Neera Tanden releases statement on pulling her nomination
PHOTO: KCAL/KCBS
Now playing
01:41
Multiple people killed in crash after SUV and semitruck collide
nigeria kidnapped schoolgirls released Busari pkg intl ldn vpx_00000423.png
nigeria kidnapped schoolgirls released Busari pkg intl ldn vpx_00000423.png
Now playing
02:09
Tears of joy and relief as 279 Nigerian schoolgirls return home
New satellite images taken by Maxar show that North Korea sometime in the past year built a structure that may be intended to obscure entrances to an underground facility where nuclear weapons or nuclear weapons components are stored.
PHOTO: Courtesy Maxar
New satellite images taken by Maxar show that North Korea sometime in the past year built a structure that may be intended to obscure entrances to an underground facility where nuclear weapons or nuclear weapons components are stored.
Now playing
01:47
See images US intelligence claims is a secret weapons site
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
PHOTO: Jeenah Moon/Getty Images
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
Now playing
02:29
NYT: Third woman comes forward against Gov. Andrew Cuomo
PHOTO: Courtesy Penguin Random House
Now playing
01:00
These 6 Dr. Seuss books won't be published anymore
John King Magic Wall 0301
PHOTO: CNN
John King Magic Wall 0301
Now playing
03:00
US coronavirus numbers coming down, but not enough
FILE - In this Jan. 29, 2011 file photo, Saudi journalist Jamal Khashoggi speaks on his cellphone at the World Economic Forum in Davos, Switzerland. Saud Al-Mojeb, Saudi Arabia's top prosecutor, is recommending the death penalty for five suspects charged with ordering and carrying out the killing of Saudi writer Jamal Khashoggi. Al-Mojeb told a press conference in Riyadh Thursday, Nov. 15, 2018,  that Khashoggi's killers had been planning the operation since September 29, three days before he was killed inside the kingdom's consulate in Istanbul. (AP Photo/Virginia Mayo, File)
PHOTO: Virginia Mayo/AP
FILE - In this Jan. 29, 2011 file photo, Saudi journalist Jamal Khashoggi speaks on his cellphone at the World Economic Forum in Davos, Switzerland. Saud Al-Mojeb, Saudi Arabia's top prosecutor, is recommending the death penalty for five suspects charged with ordering and carrying out the killing of Saudi writer Jamal Khashoggi. Al-Mojeb told a press conference in Riyadh Thursday, Nov. 15, 2018, that Khashoggi's killers had been planning the operation since September 29, three days before he was killed inside the kingdom's consulate in Istanbul. (AP Photo/Virginia Mayo, File)
Now playing
02:52
3 names mysteriously removed from Khashoggi Intel report
Protesters take cover behind homemade shields as tear gas is fired during a demonstration against the military coup in Yangon on March 1, 2021. (Photo by STR / AFP) (Photo by STR/AFP via Getty Images)
PHOTO: STR/AFP/AFP via Getty Images
Protesters take cover behind homemade shields as tear gas is fired during a demonstration against the military coup in Yangon on March 1, 2021. (Photo by STR / AFP) (Photo by STR/AFP via Getty Images)
Now playing
02:16
Footage shows tear gas, flash bangs used on protesters in Myanmar
New York Gov. Andrew Cuomo speaks during a news conference at a COVID-19 vaccination site in the Brooklyn borough of New York, Monday, Feb. 22, 2021. (AP Photo/Seth Wenig, Pool)
PHOTO: Seth Wenig/Pool/AP
New York Gov. Andrew Cuomo speaks during a news conference at a COVID-19 vaccination site in the Brooklyn borough of New York, Monday, Feb. 22, 2021. (AP Photo/Seth Wenig, Pool)
Now playing
01:12
Gov. Andrew Cuomo responds to allegations of sexual harassment
 Psaki biden White House Khashoggi Saudi Arabia sotu bash vpx _00011629.png
PHOTO: CNN
Psaki biden White House Khashoggi Saudi Arabia sotu bash vpx _00011629.png
Now playing
03:42
Bash to Psaki: Why hasn't Saudi Arabia been held accountable for murder of Khashoggi?
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
PHOTO: Jeenah Moon/Getty Images
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
Now playing
04:04
NYT: Second former aide accuses Gov. Andrew Cuomo of sexual harassment
PHOTO: CNN Weather
Now playing
02:23
Over 25 million people under threat for severe storms and flash flooding

Story highlights

Really hot days stifle baby making, a new study suggest

Climate change models predict enough warm to days to lead to about 100,000 fewer births per year

Research suggests that heat can hurt sperm health and dampen testosterone

(CNN) —  

There are so many things that can dampen your sex drive: You have a headache, you’re tired, it’s too hot outside.

According to a study, the last of those mojo-killers – and the climate change that is causing more scorching hot days – could be bringing down the birth rate in the United States.

Although the number of births in the United States went up last year for the first time since 2007, the U.S. birth rate has mostly been on the decline for at least a century. More couples have access to birth control and work opportunities for women have increased. Economic downturns, such as the recent 2007 recession, also contribute to baby busts. But the new study suggests that really hot days could also take a toll.

Researchers used historical vital statistics and other sources to look at the number of babies born about nine months after really hot days, which they defined as above 80 degrees, based on National Climate Center Data from weather stations across the United States.

The researchers found that, for every day that soared above 80 degrees – and in many cases above 90 degrees – between 1931 and 2010, there were 0.4% fewer births nine months later. The impact of one of these scorching days was that about 1,165 fewer babies were born across the United States.

Over a larger period, this could mean about 100,000 fewer births in the United States every year, based on climate change models that predict the number of these really hot days will increase from the current number of about 30 a year to about 90.

“I wouldn’t say it is the end of human civilization, but I would suggest it is going to add to the cost of climate change,” said Alan Barreca, associate professor of economics at Tulane University. Barreca is the lead author of the study, which was published Wednesday by the National Bureau of Economic Research, a nonprofit economic research organization.

Although previous research has supported the idea that heat hurts fertility, one of the advances of the current study, Barreca said, is that it asks the question whether fertility ramps back up when temperatures cool down. The answer? Not much.

There was an uptick in babies born between 11 and 13 months after heat spells, suggesting that couples put off their procreation by a couple of months, but this increase only made up for 32% of the decline at nine months.

“People might be constrained to conceiving in certain calendar months because they have time off work,” Barreca said. And if those precious few days in the month that a woman is fertile are thwarted by hot weather, that could be it for the year, he added. The authors did not look at whether birth rate rebounded more than the initial 32% in the years after a heat spell.

The fact that birth rates drop nine months after temperatures spike suggests that hot weather is having a direct effect on fertility, Barreca said. Although the study notes that rising temperatures can wreak havoc on income levels and food prices, both of which could discourage couples from having children, these factors would probably have more of a delayed effect on birth rate. It might take several months, for example, before a heat spell affects harvest and drives up food prices, for example.

It is easy to guess how things could cool down in the bedroom as they heat up outside. Just feeling uncomfortable could decrease, as the authors call it, “coital frequency.” But studies suggest high temperatures can also hurt reproductive health, by impairing sperm function, reducing testosterone levels and interfering with menstruation.

However, temperature probably has a lot less effect on when people have children than it did decades ago, when fewer people had air conditioner units and more people worked outside, said Kevin Bakker, a graduate student in ecology and evolutionary biology at the University of Michigan, who was not involved in the current study.

Instead, factors such as the type of work people do have probably had more of an effect on decreasing the U.S. birth rate, Bakker said.

Barreca agrees with this assessment.

“Temperature’s role has probably been pretty negligible compared to other things like access to birth control (and) increasing labor opportunities for women … but it would suggest that, if anything, it’s adding on to the other things going on,” he said.