The warming effects of burning coal are well known, and studies have shown that using the dirtiest fossil fuel around can cause cooling, too.

This is not good news, though. A new study, by Singapore scientists, shows that the cooling could result in less rainfall and raise water stress in some countries - especially in developing Asia - where the use of coal looks set to rise.

Burning coal does not release just heat-trapping carbon dioxide but also pollutants such as sulphur dioxide, which reacts with chemicals in the air to form tiny sulphate particles called sulphate aerosol.

If the sulphur dioxide is not removed before gases from burning coal are discharged into the atmosphere, the resulting particles can induce cooling in two ways.

First, the tiny particles reflect sunlight away from the earth and prevent it from reaching the ground.

Second, when water vapour condenses on the sulphate particles, cloud droplets can be formed. This may increase cloud cover, which also prevents the sun's rays from heating up the ground.

This cooling could, in turn, cause monsoons - which bring rain - to weaken or shift away from parched land. This is because monsoons are sensitive to changes in surface temperature patterns. Increased coal use, and hence sulphate aerosols, in Asia could cause widespread cooling of the Northern Hemisphere.

This could cause tropical rainfall to shift southwards, suppressing the monsoons and taking rain away from parched land.

The Singapore study, based on climate modelling, was done by Dr Benjamin Grandey from the Singapore-MIT Alliance for Research and Technology (Smart), in collaboration with Ms Haiwen Cheng, a Singapore-MIT undergraduate research fellow, and Dr Chien Wang from the Massachusetts Institute of Technology (MIT).

The study was published in April in the Journal Of Climate.

Dr Grandey said: "Greenhouse gases such as carbon dioxide have a cumulative effect on the atmosphere and it takes a while to see their impact.

"However, pollutants such as sulphur dioxide can impact the climate almost immediately."

To illustrate this, he and his colleagues investigated two scenarios of sulphur dioxide emissions from Asia, including China and India, using climate models that take into account factors such as surface temperatures, rainfall and emissions from burning coal.

The first scenario depicts high coal use in Asia by 2030, when sulphur dioxide from the region's industrial, energy and domestic sectors is increased to twice its year 2000 values. Year 2000 is a commonly used reference year for aerosol emissions.

The other scenario is based on a future in which Asia experiences less emissions by then, either through the use of renewable energy, cleaner fuels such as natural gas, or the widespread adoption of technology that cuts the amount of sulphur released into the atmosphere.

The results suggest that - unlike in scenario two - the high coal use future and higher sulphur dioxide emissions depicted in scenario one could suppress rainfall in China, India and across South-east Asia.

This is because when rainfall shifts from the Northern to the Southern Hemisphere, it no longer falls on land masses in Asia. Instead, it rains in the Indian Ocean.

Besides leading to more water stress in Asia, the Asian emissions of sulphur dioxide may suppress rainfall in the Sahel region of West Africa, a drought-prone region.

Figures from the US Energy Information Administration show that in 2012, China used the most coal: 47 per cent of the global total. This was followed by the United States at 11 per cent, and then India at 9 per cent.

But Dr Grandey pointed out that countries in the West had already gone through industrial revolutions and that the high use of coal in Asia is understandable as countries in the region seek to develop further.

In order to reduce sulphur emissions, coal power plants should be fitted with "catalytic converter- like" technology that can remove sulphur before it is discharged into the atmosphere.

But ultimately, the amount of coal being burnt should be reduced.

"Not only would this lead to reduced emissions of sulphur dioxide, with immediate co-benefits for air quality and water resources, but it would also lead to reduced emissions of carbon dioxide, with major long-term benefits for climate," said Dr Grandey.

Associate Professor Koh Tieh Yong, a weather scientist at SIM University, said the study did not raise carbon dioxide emissions while increasing aerosol emissions.

He said: "This assumption is not realistic but aids to separate greenhouse-gas effects from aerosol effects to advance scientific understanding," he said.

He added that computational studies such as Dr Grandey's help to highlight the importance of controlling aerosol emissions in efforts to mitigate climate change.

"Ultimately, whether they have any impact on such efforts depends on the decisions of policymakers who weigh environmental concerns together with societal needs and economic feasibility."