How Climate Change Affects Our Brains

(Editor’s note: This article from a past issue of Brain World magazineIf you enjoy this article, consider a print or digital subscription!)

Call it what you want — global warming or climate change — but we can all agree that it isn’t beneficial for anyone. In fact, the latest studies are beginning to show just how much of an impact climate change has had in the past, is currently having, and may have on the way human beings evolve in the future.


In case you haven’t noticed, we have big heads — and that’s no joke. Human beings have unusually large brains, with capacity for language, abstract thought, and consciousness. Until now, scientists and academics have struggled to find the reason for this, but lately a new theory suggests that the mystery behind these big-brained heads of ours lies in climate change.

Mark Maslin, geography professor at University College London, introduced the idea in 2009 and elaborated on it in a recent paper. Millions of years ago, slow changes in the Earth’s orbit dramatically impacted the east African climate, and may have played a vital role in driving human evolution, according to what’s known as the pulsed climate-variability hypothesis. “It seems modern humans were born from climate change,” Maslin said in a press statement, “as they had to deal with rapid switching from famine to feast — and back again. The climate of east Africa seems to go through extreme oscillations, from having huge, deep freshwater lakes surrounded by rich, lush vegetation to extremely arid conditions — like today — with sand dunes in the floor of the Great Rift Valley. These changes resulted in the evolution of a new species with bigger brains and also forced humans to disperse out of east Africa.”

The co-author of the study, Dr. Susanne Shultz of the University of Manchester, said, “We found that around 1.9 million years ago a number of new species appeared, which we believe is directly related to new ecological conditions in the East African Rift Valley, in particular the appearance of deep freshwater lakes. Among these species was early Homo erectus, with a brain 80 percent bigger than its predecessor.”


The recent ecological shifts in Africa might have made our brains larger, but they also might have made our tempers shorter. If you’ve stood in line for concert tickets on a hot, muggy day and almost punched someone in the face because they tried to wriggle their way in front of you, you know what we’re talking about. Turns out, temperatures can often alter our moods and behaviors; extremely high temperatures can be blamed for the aggressiveness that sometimes bubbles away inside of us. Hotheaded? Literally, some scientists believe.

In fact, a recent study conducted by researchers at the University of California, Berkeley, with Princeton University revealed that “Shifts in climate are strongly linked to human violence.” Even minor changes in temperature or rainfall showed a 4 percent increase in the likelihood of personal violence and crimes such as murder, assault, rape, and domestic violence, and a 14 percent increase in the likelihood of intergroup violence such as riots, ethnic violence, and civil wars.

In a media interview, U.C. Berkeley’s Marshall Burke stated, “This is a relationship we observe across time and across all major continents around the world. The relationship we find between these climate variables and conflict outcomes are often very large.” Researchers looked at 60 studies from around the world with data spanning hundreds of years. Their findings include an increase in domestic violence in India during droughts, and a spike in assaults and rapes during heat waves in the U.S. “You don’t want to attribute any single event to climate in particular,” Burke told the media. “But there are some really interesting results.”

Scientists are still not sure why the threat of violence increases with rising temperatures. But climate change could lead to intensified droughts and higher rainfall, resulting in floods that could potentially cause food and water scarcity, displacement, loss of homes, and loss of incomes, which could all impact the health of society and lead to heightened crime.

To find out the exact impact of climate change on violence, economist Matthew Ranson, part of a social-policy think tank called Abt Associates in Massachusetts, decided to put together some data. He studied monthly figures from the FBI’s Uniform Crime Reports database, which collects crimes recorded by police from nearly 3,000 U.S. counties between 1980 and 2009. He combined them with daily weather information to figure out how the crime rates varied and how they correlated with maximum daily temperatures.

The study, which was published in the Journal of Environmental Economics and Management, predicted that between 2010 and 2099 climate change will lead to an extra 22,000 murders, 180,000 rapes, 1.2 million aggravated assaults, 2.3 million simple assaults, 260,000 robberies, 1.3 million burglaries, 2.2 million cases of larceny, and 580,000 vehicle thefts in the U.S. alone. The cost of these increased rates of violence? Roughly $38 billion to $115 billion.

“There are many other factors that affect crime, ranging from the economy to culture to changes in socioeconomic factors,” Ranson told the media in interviews, adding that a warmer world would still be a force playing in the background. “There has been a strong historical relationship between temperature and crime, and that is likely to continue in the future. Climate change is going to affect our lives in a variety of ways. It is going to affect the social fabric of the places where we live.”

The broader context, he said, is that climate change could influence our lives in a number of ways beyond how much water we can spare for farming and such. “Now, there is reason to believe it will also impact social connections in our neighborhoods, the amount of time we allow our children to spend outside, and how much we are willing to spend on law enforcement.”


Scientists increasingly believe that rising temperatures are contributing to a wide variety of diseases that are spreading and becoming common across different parts of the world. In 2009, the Natural Resources Defense Council released a report that stated, in part, “Global warming threatens to further exacerbate the spread of many infectious diseases because increases in heat, precipitation, and humidity can foster better conditions for tropical and subtropical insects to survive and thrive in places previously inhospitable to those diseases.”

Dengue fever, it said, was on top among those diseases. Also known as breakbone fever, dengue fever has had an alarming rise in recent years, particularly in hot and humid countries like Brazil and India. It claims thousands of lives each year and is treated like an epidemic. Once considered a disease exclusive to the tropics, dengue fever has increased by thirtyfold in the last five decades and has spread to wider regions, including 28 states in the U.S.

“Warmer temperatures boost the speed of development of adult mosquitoes, increasing their numbers,” the report said. “Female mosquitoes bite more frequently in hotter temperatures, and warmer winters enable mosquitoes to survive in areas that were formerly too cold. Higher temperatures also shorten the time it takes for the virus inside the mosquito to develop and become infective.” While dengue fever may be the biggest of our worries, it’s not the only one.

Another unpleasant creature that thrives in warmer waters and has been spotted more frequently in recent years is the Naegleria fowleri, or N. fowleri, which, according to the Centers for Disease Control and Prevention (CDC), is “a heat-loving amoeba. As water temperatures go up, it thrives. In future decades, as temperatures rise, we’d expect to see more cases.” N. fowleri is particularly nasty. Lurking in water and inhaled during a swim on a hot summer’s day, it travels through the nasal passage of the victim and into the brain, where it feeds on cerebral fluid and gray matter, eventually leading to the victim’s death.

Then there’s valley fever, which infects more than 150,000 people per year. It was historically found only in the dry regions of the Southwest but has now been spotted in eastern Washington as well. Tick season seems to last longer too, starting earlier and ending later.

In fact, there are a number of organisms that are exhibiting changed behaviors as a result of climate change that could affect human health in the years to come. Global warming is responsible for doubling bark-beetle mating, which leads to an increase in tree attacks as much as 60 fold. It results in other huge environmental impacts, such as a decline in shelled creatures that could trigger an explosion in jellyfish populations.

Recently, scientists at Harvard have been worried about how climate change will make invasive plant species even more dominant in the landscape. Charles C. Davis, researcher and assistant professor at Harvard’s Department of Organismic & Evolutionary Biology said, “Invasive species can be intensely destructive to biodiversity, ecosystem function, agriculture and human health,” According to him, “In the United States alone, the estimated annual cost of invasive species exceeds $120 billion. Our results could help in developing predictive models to assess the threat of future invasive species, which may become greatly exacerbated in the face of continued climate change.”

(Editor’s note: This article from a past issue of Brain World magazineIf you enjoy this article, consider a print or digital subscription!)


Be the first to comment

Leave a Reply

Your email address will not be published.