Heatwaves are becoming 'more intense' and more frequent due to climate change
Climate change is 'unequivocally' linked to some extreme weather events such as heatwaves, but its effect on others, such as severe droughts may be overestimated, a new study suggests. In the last three months, monsoon rains unleashed disastrous flooding in Bangladesh, and brutal heatwaves seared parts of South Asia and Europe. Meanwhile, prolonged drought has left millions on the brink of famine in East Africa. A review of extreme weather hazards shows that climate change is making heatwaves more intense and more likely, and the impact in terms of lives lost and financial costs is being underestimated. For others, including tropical cyclones, there are variations between regions and the role that climate change plays in each event. But severe droughts in many parts of the world are not due to climate change, according to the review by scientists from University of Oxford, Imperial College London and the Victoria University of Wellington, New Zealand. Study co-author Friederike Otto, of Imperial College London, said the impact of global warming on extreme weather events was often 'overestimated'. 'I think on the one hand we overestimate climate change because it's now quite common that every time an extreme event happens, there is a big assumption that climate change is playing a big role, which is not always the case,' she told the . 'But on the other hand, we really underestimate those events where climate change does play a role in what the costs are, especially the non-economic costs of extreme weather events to our societies.' The researchers looked at information from the latest reports from the UN's Intergovernmental Panel on Climate Change (IPCC) and results from the growing body of attribution studies, which use weather observations and climate models to identify the role of global warming in specific events. Dr Otto said it was 'absolutely' the case that climate change was already making heatwaves more likely and intense. 'We can very confidently say that every heatwave that is occurring today is made more intense and more likely because of climate change. 'There are local factors like land use changes that might change how much more likely, but there's no doubt climate change is really an absolute gamechanger when it comes to heatwaves around the world,' she added. However, in other extremes, such as drought, the role of climate change is less clear. Dr Otto pointed to East Africa, which has a naturally highly variable climate that contributes to drought, and warned that disaster there was linked to poverty and lack of health care systems and infrastructure. The study authors say there is a need to record the impact of extreme weather far more systematically around the world, as a lack of data on previous events makes it harder to cope with future extremes. Lead author Ben Clarke, of the University of Oxford, said: 'The rise of more extreme and intense weather events such as heatwaves, droughts and heavy rainfall have dramatically increased in recent years, affecting people all over the globe. 'Understanding the role that climate change plays in these events can help us better prepare for them. It also allows us to determine the real cost that carbon emissions have in our lives.' In general, a heatwave that previously had a 1 in 10 chance of occurring is now nearly three times as likely and peaking at temperatures around 1 degree Celsius higher than it would have been without climate change. An April heatwave that saw the mercury climb above 122F (50C) in India and Pakistan, for example, was made 30 times more likely by climate change, according to the climatologists leading the international research collaboration World Weather Attribution. Heatwaves across the Northern Hemisphere in June from Europe to the US show that 'the frequency of heatwaves has gone up so much,' Dr Otto said. Overall, episodes of heavy rainfall are also becoming more common and more intense because warmer air holds more moisture, so storm clouds are 'heavier' before they eventually break. However, the impact varies by region, with some areas not receiving enough rain, the study suggests. Last week, China saw extensive flooding, following heavy rains, while Bangladesh was hit with a flood-triggering deluge. Scientists have a harder time figuring out how climate change affects drought. Some regions have suffered ongoing dryness, with warmer temperatures to the west of the US melting the snowpack faster and driving evaporation. And while East African droughts have yet to be linked directly to climate change, scientists say the decline in the spring rainy season is tied to warmer waters in the Indian Ocean. This causes rains to fall rapidly over the ocean before reaching the Horn. Heatwaves and drought conditions are also worsening wildfires, particularly megafires which are those that burn more than 100,000 acres. Fire raged across the US state of New Mexico in April, after a controlled burn set under 'much drier conditions than recognized' got out of control, according to the US Forest Service. The fires burned 341,000 acres. On a global scale, the frequency of storms hasn't increased, the researchers said, but cyclones are now more common in the central Pacific and North Atlantic. They are less common in the Bay of Bengal, western North Pacific and southern Indian Ocean, the study added. There is also evidence that tropical storms are becoming more intense and even stalling overland, where they can deliver more rain on a single area. So while climate change might not have made Cyclone Batsirai any more likely to have formed in February, it probably made it more intense, capable of destroying more than 120,000 homes when it hit Madagascar. The new research has been published in the journal .