How climate change is powering cyclones like Hale
In an alternate world where humans never burned fossil fuels, ex-Cyclone Hale would be less wet and wild. The remnants of the tropical cyclone are forecast to bring heavy rain and strong wind this week. Civil Defence warned the storm is likely to be a significant event with widespread effects. Climate scientist James Renwick said the heating atmosphere is expanding the width of the tropical zone where cyclones form. Theyre forming a little bit further away from the equator... In a sense, the tropics are getting bigger. Tropical cyclones will be able to form over larger areas. Human-produced greenhouse emissions have already heated the planet by an average of roughly 1.2C, compared to the pre-industrial world. This additional warmth is already affecting tropical cyclones, according to the worlds leading climate researchers. In its most recent report on the effects of global heating, the Intergovernmental Panel on Climate Change (IPCC) concluded that tropical cyclones are becoming more costly . Until the world reaches net-zero emissions, weather events will become increasingly extreme, said Renwick an IPCC author and Victoria University researcher. Tropical cyclones havent increased in number. They have increased in intensity, he added. READ MORE: * Summer of cyclones? High sea temperatures put NZ on elevated alert * Is climate change to blame for the summer washout? * Summer of cyclones? Warmer seas and weather phenomenon play into elevated alert level for New Zealand To Tuesday, nearly a months worth of rain fell in Northland and north Auckland in just 24 hours. Thats on top of the moisture brought by last weeks concentrated downpours . When water vapour condenses back into liquid water, forms a cloud and rains that releases a lot of energy into the air, Renwick said. By increasing the temperature, youre increasing evaporation and increasing the amount of water vapour in the air. Thats more fuel for the growth of these storms and that applies to all storms. The heating atmosphere is also warming the ocean. Tropical cyclones get their energy directly from the sea surface, Renwick said. If youve got more energy to work with, youre more likely to get a powerful storm that will grow faster. In general, stronger storms will produce fractionally more powerful winds, he added. If the winds are already blowing at 150kph, another 10% is quite a lot. Once these storms leave the tropics, they are no longer tropical cyclones . The remnants reform over the cooler sub-tropical and temperate oceans though as ex-Cyclone Hale shows, can still unleash strong winds and heavy rain. Well continue to see these storms coming to New Zealand, Renwick said. When they come, because theyve been more powerful in the tropics, chances are theyll be more powerful and damaging. When they do make landfall in Aotearoa, the storms will also meet higher seas at the coastline another effect of the warmer ocean, Renwick said. In parts of New Zealand, sea level rise is being exacerbated by the sinking of land. When you have a big storm, and youve got onshore winds and a storm surge, that extra few centimetres of sea level can make a big difference to how far storm waves can get inland. Our weekly email newsletter, by the Forever Project's Olivia Wannan, rounds up the latest climate events. Sign up here .