The Earth's temperature is rising steadily, and by 2050 six countries will be extreme-heat countries, Bangladesh among them. A new study from the University of Oxford says the effects of this extreme heat will be most severe, and warns of the impact of heatwaves on natural life, the economy and public health. The research, led by Oxford researchers, was published in the journal Nature Sustainability on 26 January.

The study says that if the current use of fossil fuels continues, the number of people living in extreme heat could almost double in the next 25 years. It estimates that if global warming reaches 2C above pre-industrial levels, about 41 per cent of the world's people, about 3.79 billion, will be living in extreme heat by the middle of the century. In 2010 the figure was 23 per cent, or about 1.54 billion.

The researchers assessed heat risk using the 'cooling degree days' (CDD) index with high-resolution climate and population models. Areas with more than 3,000 CDD a year were classified as 'extremely heat-prone'. The index shows how much cooling is needed to keep indoor temperatures safe.

By this index, the countries with the most people living in extreme heat include India, Nigeria, Indonesia, Bangladesh, Pakistan and the Philippines. Oxford's lead researcher, Dr Jesus Lizana, said national average temperatures often mask the real risk. In Bangladesh most people actually live in areas where the annual cooling demand exceeds 3,000 CDD, meaning long exposure to dangerous heat that affects people's lives, productivity and health.

The study notes that Bangladesh is already one of the world's most climate-vulnerable countries. While sea-level rise, cyclones and floods have long been discussed, extreme heat is emerging as an invisible but equally deadly threat. Experts say rising heat significantly increases the risk of heatstroke, cardiovascular stress and kidney disease, particularly among older people, children and people on low incomes with limited access to cooling.

The Oxford-led study also found that demand for cooling will rise fastest in low- and middle-income countries in tropical and subtropical regions, while in wealthier northern countries warmer winters will reduce heating demand. The countries worst affected by the rise in cooling degree days per person will be the Central African Republic, Nigeria, South Sudan, Laos and Brazil. By contrast, heating demand will fall in Canada, Russia, Finland, Sweden and Norway as winter temperatures rise.

The researchers also warn that heavy use of cooling in extreme-heat countries could create a 'cooling trap': if it is met with fossil fuels, climate change will accelerate further. The findings make clear that the window for preventing the harmful effects of extreme heat is closing fast. The scientists say that if global warming can be kept close to 1.5C above pre-industrial levels, the number of people exposed to deadly heat can be reduced significantly.

Meanwhile, scientists have identified a new reason for the Earth's rapid warming. They say glaciers are melting and sea-surface temperatures are rising, and last year the planet set a new warming record. Scientists are trying in various ways to understand why the Earth keeps getting warmer. There are several causes, among them the growing use of fossil fuels and natural phenomena such as El Nino. But the speed at which the Earth is warming cannot be explained by these known causes alone. A research report published last Thursday identified a new factor.

The main finding of the report, published in the journal Science, is that clouds play a part in the Earth's rapid warming. The new research found that low cloud cover over the oceans has declined rapidly, which is contributing significantly to warming and could cause various problems in future. Helge Goessling, an author of the report and a climate physicist at Germany's Alfred Wegener Institute, said fewer bright, low clouds mean the Earth has become 'darker'. This relates to albedo, the share of sunlight reflected and scattered from the Earth back into space as short waves.

The research found that the Earth's albedo has been falling since the 1970s. Scientists believe that, among other causes, this is because light-coloured snow and sea ice are melting, increasing the darker areas of ocean and land that retain more of the sun's heat, and so the Earth is warming. For the new research, scientists used NASA satellite data, weather data and various climate models. They found that last year low clouds reduced the Earth's albedo by a record amount, with a notable fall over the North Atlantic.

Goessling told CNN that low cloud cover fell as much in the past year alone as it usually falls in a decade. Why this is happening cannot yet be explained; it is quite hard to explain. The main cause of the rise in global temperatures, however, is human activity, which is increasing greenhouse gases in the atmosphere and warming the Earth.

Source: Jagonews24. First published in Bengali on The Agro News.