more than 3 billion people could potentially end up living in unbearable heat in the next 50 years, a new study published in the proceedings of the national academy of sciences of the united states of america showed.  while the worst-case scenario says 3 billion people may be impacted, the associated press reported that the more likely scenarios from the study show that at least one billion people will be affected.  the number of people impacted depends on what action is taken to reduce carbon emissions.  there are currently 20 million people impacted by extremely high temperatures.  visit business insider's homepage for more stories.  as many as half of the current world's population could be dealing with "unlivable heat" by 2070, a new study published in the proceedings of the national academy of sciences of the united states of america showed.  in the next 50 years, somewhere between 1 to 3 billion people are expected to be inflicted with unbearable heat, according to the study. by 2070, that could be about a third of the overall global population at that time.  marten scheffer of wageningen university in the netherlands, an ecologist and co-author of the study, told the associated press the projections are "unlivable for the ordinary, for poor people, for the average world citizen."  the actual number of people affected will depend on how fast the global population grows and the levels of carbon emissions, the ap reported.  while the worst-case scenario expects over 3 billion people to be impacted, more likely scenarios from the study show that at least 1 billion people will be affected, the ap reported.  "it's a huge amount, and it's a short time. this is why we're worried," cornell university climate scientist natalie mahowald told the ap.  mahowald wasn't apart of the study but told the ap that "the new study makes sense and conveys the urgency of the man-made climate change differently than past research."  scheffer told the ap that for every 1.8 degrees fahrenheit increase in global average annual temperature "from man-made climate change," about a billion people will end up in areas too warm to live.  greenhouse gas emissions have to be reduced so average annual temperatures don't rise beyond the approximately 52 to 59 degrees fahrenheit yearly average that humans have been able to thrive in for the past 6,000 years, usa today reported.  "we show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 years than it has moved (in the past 6,000 years)," the study said.  the ap reported that the range was found after scientists looked at "humans like they do bears, birds, and bees to find the 'climate niche' where people and civilizations flourish." while humans can live in hotter and colder weather, the further away from that range the harder it is.  the researchers looked at areas most likely to experience the change in range and estimated that around 2 billion people will be living there in the next 50 years.  the study found that large parts of africa, asia, south america, and australia are likely to increase their temperature similar to what 20 million people are already experiencing in places like the sahara desert where the annual average temperature is more than 84 degrees fahrenheit, the ap reported.  "large areas of the planet would heat to barely survivable levels and they wouldn't cool down again," scheffer told usa today. "not only would this have devastating direct effects, it leaves societies less able to cope with future crises like new pandemics. the only thing that can stop this happening is a rapid cut in carbon emissions."
3 billion people — up to half the current global population — could be living in unbearable heat in 50 years