When we have a hot spell such as we experienced over recent days, I have always secretly hoped that the highest temperatures would be recorded in an appropriately named Irish weather station, such as Newport Furnace in Co Mayo or Ovens in Co Cork. However, Shannon Airport took the prize on Tuesday last with a maximum temperature of 30.6 degrees, thus for the second day in a row breaking the almost 30-year record of the hottest day in May previously held by Ardfert in Kerry. But what was remarkable about last week was that these temperatures did not just break previous records by the usual 0.1 or so degrees but demolished them by a full 2 degrees or more. Something exceptional was occurring.The mechanics of the hot spell were fairly similar to previous events. A large stationary anticyclone was facilitating a plume of hot air reaching Ireland from the near continent and ultimately from North Africa. The heat dome this descending air produced effectively trapped heat close to the surface rather like putting a lid on a saucepan being heated from below. But other ingredients were also apparent. Somewhat unusually, the air higher up in the atmosphere was coming in for a time from a rather cold source, namely the western Atlantic and even eastern Canada. As this made its way across the Atlantic it was forced to descend under the European anticyclone, compressing and heating it up, and ultimately adding further to the heat dome at the surface.Extreme temperatures such as we had last week cannot be seen to be other than a consequence of Ireland’s warming climate. Although Ireland has warmed by around 0.7 degrees over the past 30 years, such a change in average conditions provokes a much greater change in extremes. Most recently we have seen this with rainfall extremes in an Ireland 7 per cent wetter than 30 years ago. The Intergovernmental Panel on Climate Change estimates that the kind of extreme temperature that in the past occurred maybe once in 10 years will occur once in four years as the world approaches 1.5 degrees of warming.All this would be less unexpected if it was happening in June or July. But to have such a hot spell in May is quite astonishing. Across western Europe the temperature records tumbled. London hit 35 degrees, as did many parts of France and Spain. Europe as a whole is now warming twice as fast as the global average.Such extreme temperatures have health consequences. Nine out of 10 deaths from extreme weather events in Europe are caused by heat. The heatwaves of last summer drove an estimated 16,500 additional deaths across 854 European cities. People aged 65 and over made up 85 per cent of the estimated deaths. A particularly brutal heatwave in Paris in August 2003 killed 15,000 people and 70,000 elsewhere on the continent. As a result many countries have since developed heat-health action plans, something that will have to be implemented also in Ireland. [ Recent record temperatures ‘rose 10 times faster than expected in stable climate’Opens in new window ]In Ireland most temperature-related excess deaths have historically occurred in winter, a consequence of a poorly insulated housing stock. But in some work I was associated with, years back, more than 100 excess deaths were recorded during an Irish heat event, and it is clear that, as temperatures rise, the balance will increasingly swing to summer mortality increases. Of course this will be particularly the case for vulnerable populations, such as the elderly, very young and unborn. What was also noted in that work was the tendency for Irish excess mortality to begin to increase at temperatures less than in other countries. Put simply, we are not acclimatised to higher temperatures than we normally experience, unlike our continental neighbours. In addition, warm conditions stress the natural environment in many ways. They also tend to exacerbate water borne and food borne diseases such as salmonella. Good weather brings out the barbecues and increased risks associated with undercooking of poultry and other meats.Looming over the next few months is another phenomenon, this time a natural event: El Niño. Already the eastern Pacific Ocean has warmed by up to 3 degrees and a warm tongue of water is beginning to develop westwards across the equatorial zone. This will ultimately rearrange the climate deck of cards in many parts of the tropics, provoking droughts in Australia and northern Brazil, summer droughts in southern Africa, floods in Ecuador and Peru and increased rainfall in south western parts of the US. While the signal is much weaker in mid latitude locations such as Ireland, there will be unforeseen consequences in the interconnected world we now inhabit. Thankfully, oceans act as the world’s great climate buffer, absorbing more than 90 per cent of the excess heat generated by human-driven greenhouse gas emissions. But, partly as a result of the already warmer global ocean, this coming El Niño is expected to be much more pronounced than normal, causing a spike in global warming from 1.5 degrees to 1.73 degrees.The key question is: “If Ireland has a hot spell this bad in May, what will July and August bring?” That’s impossible to answer, but rolling the climate dice suggests more frequent, more extreme events will continue to occur until the world ends its reliance on fossil fuels. Former Nasa director James Hansen estimated in 2012 that the energy disturbance to the Earth’s climate system from greenhouse gas accumulations was equivalent to exploding 400,000 Hiroshima atomic bombs per day, 365 days per year. But this was 14 years ago and updating those figures suggest at least a doubling is now appropriate.So we have chosen to live in a climate on steroids in which extremes such as last week will become the norm and not the exception. Some of the aforementioned Irish placenames may prove very appropriate.John Sweeney is emeritus professor of geography, Maynooth University and a climatologist