Earth is spinning at around 1,040 miles per hour so if two points are equidistant from our equator, they should be equally warmed by the Sun. But that isn’t the case, and it could have significant consequences for our planet. A study looking at 24 years of Nasa satellite surveys found that the Earth is actually getting darker, and there are massive differences between the northern and southern hemispheres. So, what’s going on? (Picture: Getty)
A team of researchers used data from the Clouds and the Earth’s Radiant Energy System (CERES) satellite to find that the northern hemisphere (NH) is getting darker than the southern hemisphere (SH), and that it could be a big problem for our planet. The researchers, led by Dr Norman Loeb from the Langley Research Center in Virginia, revealed the northern hemisphere experiences a net loss of radiative energy compared to the southern hemisphere (Picture: Getty)
This means that the northern hemisphere absorbs more light and therefore reflects less light, so if you were to look at the Earth from space, you would see that the northern hemisphere would look dimmer as a result of this lack of reflection. The researchers published their findings in the journal PNAS (Picture: Getty)
But why does this matter?
This could affect our climate. The issue affects the amount of light the planet absorbs and re-emits into space as outgoing longwave radiation. Usually, this would be rectified by the oceanic currents that transport energy from the southern hemisphere to the northern hemisphere but now the balance has changed so much that the ocean currents have not been making up the differences – for the last 20 years (Picture: Getty)
The authors wrote: ‘The emerging darkening of the NH relative to the SH is associated with changes in hemispheric differences in aerosol–radiation interactions, surface albedo, and water vapor changes. How clouds respond to this hemispheric imbalance has important implications for future climate.’ The researchers explain that one of the drivers is albedo – the reflectivity of the Earth’s surface. As the arctic sea ice is rapidly melting, the Earth’s reflective surfaces, such as snow and ice, is being replaced with more light-absorbing surfaces like land and sea water (Picture: Getty)
Another reflectivity source is clouds. And research has found that low-lying clouds have decreased in the recent decades, and this could partly be due to the fact that the northern hemisphere is polluting less than it used to, as aerosols (the tiny particles that make various forms of air pollution) can act as seeds for cloud formation — fewer seeds means fewer clouds. The researchers said: ‘Since the NH darkening (relative to the SH) due to noncloud property changes (aerosol–radiation interactions, surface albedo, water vapor) is not compensated by cloud changes, this suggests that there may be a limit to clouds’ role in maintaining hemispheric symmetry in albedo’ (Picture: Getty)
The team also found that the northern hemisphere is warming relative to the southern hemisphere, and that the northern hemisphere tropics are also getting wetter, suggesting a change in large-scale atmospheric circulation on the planet. The experts say that more research is needed but the northern hemisphere could continue to warm more quickly than the south (Picture: Getty)
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