John Sweeney is Ireland’s leading expert on climate science, and a Professor of Geography at NUI Maynooth.He was a contributor to the Fourth Assessment Report of the IPCC, which was published in 2007. The IPCC shared the 2007 Nobel Peace Prize. Professor Sweeney was the keynote speaker at a Stop Climate Chaos briefing on the latest IPCC report, which took place in Dublin’s Science Gallery earlier today.You can follow Stop Climate Chaos on Twitter @SCC_Ireland and on Facebook. The Twitter hashtag for the publication of the IPCC report is #IPCCAR5. IN JANUARY 1839, a major winter storm hit Ireland. Homes, shops and farms were destroyed, and several hundred people lost their lives. In Dublin alone, nearly a quarter of houses were damaged, and 42 ships were wrecked. It is said the wind carried seashells as far inland as Athlone.This event was so unprecedented and had such catastrophic consequences that ‘Oíche na Gaoithe Móire’ (the ‘Night of the Big Wind’) became embedded in Irish folklore. More than that – at a time when few births were recorded and illiteracy levels were high – it became a measure by which people could gauge their age. Seventy years later, when the State pension was established and many could not prove their date of birth, they were asked if they could remember the ‘Big Wind’; if they could, they were old enough for the pension.In the 175 years since this event, catastrophic storms – thankfully – have been an infrequent phenomenon in Ireland. In the coming decades, however, if we allow climate change to continue unchecked, extreme weather events will become more common.Extremes of heat and cold – such as we experienced in 2010 and 2011 – will be much more frequent. Summers will be hotter and drier; winters will be warmer and wetter; and a risk of more frequent widespread flooding will occur.IPCC reportThe IPCC report, part of which is published today, is the most comprehensive, authoritative and scrutinised report on climate change ever written. It was prepared by over 800 scientific experts from all over the world, and its findings have been arrived at by exhaustive review processes.What it shows is that scientists are now as positive that climate change is real and caused by humans as they are that smoking causes cancer.In the 250 years since the Industrial Revolution, mankind has emitted half a trillion tonnes of carbon by burning fossil fuels – a process that has caused atmospheric carbon dioxide levels to rise by 40 per cent. We are on track to release another half trillion tonnes in the next few decades, and this would result in a major jump in global temperatures.If this is allowed to happen, parts of the earth that are currently home to hundreds of millions of people will become uninhabitable. Droughts and floods will wreak havoc in many vulnerable regions of the tropics, and there will be mass movements of people trying to escape the consequences.Facing factsBefore I’m attacked as a harbinger of doom and gloom, let me make a few points.First, I’m a scientist: I deal with facts; not opinions and sentiment.Second, I’m an optimist. So, although I know irrefutably that climate change is real and is caused by humans, I also believe we can do something about this.The Irish contextIn Ireland, we often downplay the risks from climate change because we enjoy a temperate climate.We are a small island nation, and we feel we won’t be directly affected. But the truth is that climate change – if unchecked – will severely damage not only our environment, but also our economy and quality of life.If extreme weather becomes commonplace, there will be consequences for major economic sectors such as agriculture and food production. Uncontained climate change will cause major disruption to world trade and the global economy, and Ireland – with our open, export-led economy – will suffer as a result.The phenomenon of ‘climate refugees’ will grow, and – with our temperate climate – Ireland is likely to be viewed as a safe haven. So, in addition to the impact on our economy of climate change disruption in other parts of the world, we could also be looking at unprecedented levels of migration, and at supporting a larger population here.Good newsThe potential economic, demographic and environmental fallout from climate change is not a pleasant scenario.But the good news is we can act now to make sure it doesn’t happen. Governments throughout the world must urgently implement plans to reduce emissions, encourage clean energy and discourage the use of fossil fuels.In Ireland, the Government has published the Heads of a new Climate Action and Low Carbon Development Bill.In advancing this legislation, it is important to ensure there is an effective strategy for emissions reductions and provision for independent oversight and monitoring of progress.Finally, we must remember there’s an opportunity for Ireland here: we should incentivise private investment in a low-carbon economy and encourage our highly-skilled and entrepreneurial tech sector to focus on developing alternatives to fossil fuels.Our current depressed economic state presents a chance to rebuild in a more sustainable way. We are a small, nimble country that can react quickly, take advantage of opportunities and position ourselves to make sure we’re not a big loser because of climate change. We have the talent and the potential to become leaders in a new, low-carbon industrial revolution.Let’s act now, before it’s too late.