Thursday, November 5, 2015

Too Darn Hot! Sex, human fertility and birth rate declines due to #heatwave temperature shocks



This article originally published at nofibs.com.au.

If your not feeling like sex when it's too darn hot, your not alone. Latest research into human fertility and temperature extremes reveals that birthrates suffer a fall nine months after extreme temperatures events, and although there is a partial recovery in subsequent months, this does not make up for the lost fertility.

The research is based upon data of the effects of temperature shocks on birth rates in the United States between 1931 and 2010. It is contained in a working paper published October 2015 by Alan Barreca, Olivier Deschenes, Melanie Guldi from the US National Bureau of Economic Research and is titled Maybe Next Month? Temperature Shocks, Climate Change, and Dynamic Adjustments in Birth Rates.


This reduced fertility during summer months acts to move conception to during cooler months thus increasing the proportion of births during summer months when extreme heat may pose a greater neo-natal and post-natal health risk.

The research reflects the fact that extreme temperatures and Heat waves have been around for many years. But summer heatwaves are now starting earlier, are more frequent, and of greater intensity posing serious health issues. Recent research indicates that 75 percent of heatwaves are influenced by climate change. This latest research strongly suggest that extreme temperatures and heatwaves result in a decline of human fertility and birthrate.

Of course we are already finding ways to adapt to this issue. I won't go into such subjects as fridge sex, but humans tend to be innovative in getting it on.

The study does mention the uptake of air conditioning over recent decades as an adaptation. Which brings in other issues. As standards of living increase there is growing demand for air-conditioning which is adding to peak energy demand in summer. Increased air conditioning in urban areas also boosts the urban heat island effect providing a feedback loop between extreme temperatures and air conditioning use.

The study abstract explains:

"Our innovative approach allows for presumably random variation in the distribution of daily temperatures to affect birth rates up to 24 months into the future. We find that additional days above 80 °F cause a large decline in birth rates approximately 8 to 10 months later. The initial decline is followed by a partial rebound in births over the next few months implying that populations can mitigate the fertility cost of temperature shocks by shifting conception month. This dynamic adjustment helps explain the observed decline in birth rates during the spring and subsequent increase during the summer. The lack of a full rebound suggests that increased temperatures due to climate change may reduce population growth rates in the coming century. As an added cost, climate change will shift even more births to the summer months when third trimester exposure to dangerously high temperatures increases. Based on our analysis of historical changes in the temperature-fertility relationship, we conclude air conditioning could be used to substantially offset the fertility costs of climate change."

April 2016 Update: Queensland birth figures confirm trend


In Queensland birthrates show peaks in March and September. Women's and Family Services acting director Keppel Schafer, in an report by ABC News in April 2016, said winter weather conditions were the reason behind the March baby boom.

"The ongoing trivia that we have amongst the trade is that it's the first cool change that the coast experiences in June or July in the year before," he said. "That probably sees us very busy nine months later in the following March. I think there's a bit more snuggling under the doona and then there's a new baby in a bunny rug nine months later."

The September birth peak aligns well with Christmas festivities.

Over the ten years from 2004 to 2014, the average babies born in Queensland for March was 5,243, almost 200 more than the second most popular birth month in May.




This confirms the study by the American economists. Alan Barreca, an associate professor at Tulane University in New Orleans and an author of the research published in October 2015, commented in the ABC report:

"Around the world there are these really strong seasonal patterns in birth," he said.

"In the United States and Europe, there's actually a pretty big spike in births in the summer months, and if you go back nine months that implies that conceptions are most likely to occur in the colder winter months," Professor Barreca said.

"When you go to Australia, some of the highest birth rates are in March.

"There's also a high birth rate in September in Australia, so that story about holidays influencing fertility decisions that does seem like it's in play.

"But it's the March effect — the fact that there's a sizeable increase in births in Australia in March also suggests that temperature is in play."

"Hot temperature seems to be having the largest impact on births but in the opposite direction," he said.

"In Australia there are about 25,000 births per month across the entire country," he said.

"Our estimates suggest that for each hot day Australia experiences, nine months later we'd see a fall of about 100 births [on a single day]."

So that amounts to each hot day reducing birth rates nine months later by 0.4 per cent, according to the research.

There are two main reasons for extreme heat reducing fertility. One is behavioural: it is just too darn hot to make out and enjoy the experience.

The second is scientific and relates to the reduction in sperm motility and sperm count under high temperatures by most mammals including humans. Thonneau et al (1998) in Occupational heat exposure and male fertility: a review, concluded

"In humans, as in most mammals, spermatogenesis is temperature dependent. This temperature dependence has been clearly demonstrated by several experimental studies showing that artificial increases in scrotum or testicle temperature in fertile men reduce both sperm output and quality.... We concluded that occupational heat exposure is a significant risk factor for male infertility, affecting sperm morphology and resulting in delayed conception."

Alan Barreca gave a projection on climate change and increase in extreme temperatures on future birthrates in the ABC News article: "According to a state of the art global circulation model, there is going to be about 90 hot days per year by the end of the 21st century — that's about 60 more days than we currently experience," he said. "Using our estimates, we project that the number of births will fall by about 107,000 per year in the United States by the end of the 21st century."

Read the ABC News article by Harriet Tatham: Climate change and your birthday: Is it too hot for sex? (9 April, 2016)


Kinsey sex report found sizzling temps a turn off

Early indications of extreme heat impact on human sexual activity was revealed in the seminal Kinsey Sex reports which articulated that average men prefer cooler weather for courting and sex.

Remember that Cole Porter classic song Too Darn Hot for the 1953 film Kiss Me Kate? The movie version altered the lyrics slightly to drop the reference to the Kinsey Report. Here is an excerpt from the original lyrics:

According to the Kinsey report
Every average man you know
Much prefers his lovey dovey to court
When the temperature is low

But when the thermometer goes way up
And the weather is sizzling hot
Mr Pants, for romance, is not

I referred to this possible link between sexuality and extreme heat at the bottom of my April 2014 article on The challenge of adapting to climate change and heatwaves in Melbourne. Ann Miller in the 1953 Film Kiss Me Kate does a great rendition of Too Darn Hot with a fantastic tap dance routine that you can watch embedded in that page.


Global Population and fertility rates


Many economists who plan for continued growth will view this reduced fertility with alarm, yet each new birth in developed countries increases consumption of resources and contributes to carbon emissions causing climate change.

Population growth is a concern with more than 7 billion people on the planet. Demographic projections say another 2.5 billion people may be added by 2100. Fertility rates will be an important determinant on how population actually changes in coming decades. Replacement fertility rates (2.1 children per woman) and mortality rates typical of developed countries will result in about 10.1 billion people by 2100. Half a child above replacement rate then the population will reach 15.8 billion by 2100. Half a child below replacement rate will lead to an early peak in population and a slight decline to 6.2 billion people by 2100. (Barnosky et al 2014)



While population rates in developing countries appear to be the problem, developed countries have a much more substantial carbon foot print per capita. For example, the average US citizen used about 22 barrels of oil per year in 2011, Australia about 17 barrels of oil per capita, whereas the average person in China and India used only about 3 and 1 barrels, respectively. Solutions will require dealing with these disparities while still preserving quality of life. This will require a major transformation in reduction of consumption behaviour that affects rich nations. Science and Technological breakthroughs will help, but our whole model of consumption built on endless growth and resource exploitation needs to end.

About 40 per cent of the global population already live in countries where fertility is close to replacement, and another 42 per cent live in countries where the fertility rate is significantly lower. It is the 18 per cent of the global population that live mostly in economically disadvantaged countries, where people still lack ready access to education and healthcare that fertility rates are sill high. Raising levels of education and women's rights and providing access to safe and effective means of contraception to those who want it, are proven methods to reduce fertility rates substantially.(Barnosky et al 2014)

Population growth is a substantive contributor to climate disruption. Each person on Earth produces on average about 4.9 tonnes of CO2 per year, as of 2011, so as population grows, greenhouse gases and consequent climate disruption increase proportionately.

As population grows, more landscape and resources are used reducing habitat and directly causing biodiversity loss and species extinctions, as well as contributing to indirect impacts on ecosystems through pollution and climate change.

Ecologist and author of The Population Bomb Dr Paul Ehrlich appeared on the ABC QandA program last Monday and stated that Australia was already over-populated and is 'destroying the life support systems'.

There is only one way to keep the population relatively young and that is to keep it growing forever. It is the motto of the faith-based economic system we are all buried in - Professor Paul Ehrlich on QandA

"The ageing issue is very popular with idiotic politicians in Europe. They think that because there is an ageing population, they have got to have imports or higher birthrates in order to keep the population young. There is only one way to keep the population relatively young and that is to keep it growing forever. It is the motto of the faith-based economic system we are all buried in. A very famous economist, Kenneth Boulding, said in 1966: 'Anyone who thinks you can have infinite growth on a finite planet is either a madman or an economist.' You are going to have to stop growth." Ehrlich told the program and live TV broadcast audience.



We should be aiming to peak and then decline human global population this century. It is perhaps ironical that extreme heat events that are increasing in frequency and intensity due to climate change may lend a hand in reducing population fertility.



Based on just the data from the first 9 months of 2015, this year is heading for the hottest ever year recorded, according to the World Meteorological Organisation. With the southern summer heat well on the way in Australia with a positive phase of the Pacific Decadal Oscillation and a monster EL Nino in progress, it just might be Too Darn Hot to get it on when the mercury rises on those really stinking hot days.

Projected Result: less fertility over the heatwave months of summer and a consequent decrease in spring birthrates in 2016. Yes, this was the actual observed result in Queensland with a spike in births in March 2016.

I'll leave you with a song. Ella Fitgerald issued a fantastic version of the 1953 Cole Porter song Too Darn Hot. This was more recently remixed by RAC in a more modern format in 2013.




Sources:
  • Alan Barreca, Olivier Deschenes, Melanie Guldi (2015) Maybe Next Month? Temperature Shocks, Climate Change, and Dynamic Adjustments in Birth Rates, Maybe Next Month? Temperature Shocks, Climate Change, and Dynamic Adjustments in Birth Rates, National Bureau of Economic Research (NBER), Working Paper No. 21681 Issued in October 2015, (DOI): 10.3386/w21681
  • Anthony D Barnosky et al (2014) Introducing the Scientific Consensus on Maintaining Humanity’s Life Support Systems
    in the 21st Century: Information for Policy Makers. The Anthropocene Review 2014, Vol. 1(1) 78–109 DOI: 10.1177/2053019613516290 (Full PDF)
  • Harriet Tatham, ABC News, 9 April 2016, Climate change and your birthday: Is it too hot for sex?
  • Thonneau et al (1998) Occupational heat exposure and male fertility: a review in Hum. Reprod. (1998) 13 (8): 2122-2125. doi: 10.1093/humrep/13.8.2122
  • Photo by Flickr/Bombtwinz Bombtwinz Hawaii 2012 - Creative Commons (CC BY-NC-ND 2.0)