If global warming increases rainfall, could the extra clouds block sunlight and help cool the Earth? © Getty Images

If global warming increases rainfall, could the extra clouds block sunlight and help cool the Earth?

Asked by: Tristin Quinn, Tullamore, Ireland

The link between clouds and global temperature is complicated. On one hand, clouds block sunlight and reflect it back into space, cooling the Earth. On the other, they trap warmth radiating from the Earth’s surface, increasing temperatures.

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The balance between these two opposing effects varies from cloud to cloud. Low clouds, for example, tend to be quite opaque, meaning that they cool the planet more than they warm it.

In contrast, wispy, high-altitude clouds allow most sunlight through but are effective at preventing heat from escaping, creating a warming effect. When you add up these effects on a global scale, clouds currently have a net cooling effect on the planet, lowering global temperatures by around 5°C.

Scientists predict that climate change will increase evaporation, leading to an increase in rainfall globally – although there will be considerable variation on a regional level. But increased rainfall does not simply translate into more clouds. Instead, changing conditions will affect how and where clouds form and how they behave.

In some areas, climate change will probably cause more low clouds to form, which could offset a rise in global temperature. In mid-latitudes, however, low cloud cover is expected to decrease.

Meanwhile, the paths followed by tropical, mid-altitude storm clouds are expected to shift towards the poles, into regions with less sunlight, dampening their cooling effect. Plus, high-altitude clouds are predicted to increase in altitude, which would have a heating effect. This is because higher clouds are colder, and absorb heat radiating from Earth just as well, but retransmit more of this heat back to Earth (rather than out into space).

It’s hard to predict how much these processes might warm the planet, as they could trigger positive feedback loops, accelerating a rise in temperature. Clouds are notoriously difficult to predict with certainty, but most climate models agree that changes in clouds will have the net effect of amplifying rising temperatures.

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