Scientists say a massive volcanic eruption in Alaska more than 2,500 years ago triggered a global climate shock on the other side of the Earth that led to the fall of the Roman Republic. The eruption of Mount Okmok on an Alaskan island in the year 43 BC – an event known as 'Okmok II' – spewed ash particles that cooled the planet by shading incoming solar radiation. Scientists say this caused with a spell of extreme cold in the Mediterranean during the European summer – the second-coldest of the last 2,500 years.