Hotter summers will drive a spike in violence, suicide and self harm, the authors of a major study into the health impacts of climate change have warned. More than 150 experts from fields including climate science, health, engineering, agriculture and transport have assessed the implications of global warming on populations and warned that sweltering summers could have unexpected side effects. The new Countdown on Health and Climate Change report published in The Lancet warns that climate change ‘aggravates’ risks to mental health and wellbeing and increases aggression, violence, self-harm and suicide. Extreme events could also spark psychological problems such post traumatic stress disorder (PTSD), adjustment disorder, and depression. Speaking at a briefing in Central London Dr Nick Watts, Executive Director of the Lancet Countdown, said: “Heat also has effects in terms of what it does to our mental health. “We know that in periods of hot weather there are spikes in violence, suicide and depression. “This is most evident in a few countries like Australia but we’re now developing ways of considering that across the world.” How hot is 2018 compared to previous summers? Research suggests that extreme heat can seriously impact brain chemistry, damaging neurotransmitters which regulate emotion.  Heat is also known to increase testosterone production, which can promote aggression. Studies in the US and Australia have found that increases in mean temperature by just 1C can see suicides rise more than two per cent and increase the number of people attending A&E through self harm by 0.7 per cent. Adelaide researchers also found rising temperatures led to significant increases in admissions to A&E for assaults and an increase in ambulance call-outs by four per cent, while mental health admissions increased by six per cent. A study in 2015 found droughts lead to an increase in farmers committing suicide while last year soaring temperatures was linked to collective violence. This week a climate change report from the Met Office warned that heatwave summers such as experienced in Britain this summer would become normal in the coming decades, with temperatures rising by more than 5C. Heatwave | Read more Professor Helen Stokes-Lampard, Chair of the Royal College of GPs, said: “When it comes to heatwaves in the UK, a sense of triviality often prevails – ‘bumper summer temperatures’ or ‘barbecue weather’ are more likely headlines than any focusing on the threat to our health. “GPs and our teams witnessed the effects of this summer’s heatwave first-hand, and they are anything but trivial.” The report found that on average, everyone on Earth was exposed to an additional 1.4 days of heatwave between 2000 and 2017 compared with the period 1986-2005. And while average global temperatures rose by 0.3 per cent between 1986 and 2017 the impact on human populations was much greater. The average temperature increase people were exposed to over the same period was 0.8C. Heat rising above physiological limits also made sustained work more difficult or impossible, the authors said. In 2017, 153 billion hours of labour were lost due to heat exposure, an increase of 62 billion hours since 2000.