How Climate Change Affects Our Brains

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.

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