Does the Sun influence climate regionally?

When the Sun is most active it is covered in dark sunspots. During this period of high solar activity the Sun's overall energy output increases.

Figure 1: When the Sun is most active it is covered in dark sunspots. During this period of high solar activity the Sun’s overall energy output increases.

In climate science, uncertainties can hide in the brightest of places. We are just now beginning to understand that the Sun’s effect on our planet may be even more complicated than we thought before. It may even affect the climate not just globally, but on a regional scale too.

Climate change is considered the greatest risk to civilization faced by man. The issue is thrust into our lives on a daily basis from every media outlet. While science is the foundation of all these claims, it comes with the caveat: there are some things that are simply unknown. That does not mean that science is wrong, but without knowing every fact, scientists cannot make an exact prediction. Like a novice darts player from eight feet away: he is going to hit the board, but just where exactly is where the uncertainty lies.

So when scientists say that climate change is the result of mankind altering the make-up of Earth’s atmosphere, the theory and the evidence is overwhelmingly robust. But, Britain has, in recent years, experienced some of the coldest winter months since records began. In a time when the world is supposedly warming, it raises the question of what is really going on.

Disentangling all the elements that affect Earth’s climate is a major task that thousands of scientists from many disciplines undertake. It is a complex issue with many influences: carbon dioxide levels, oceanic heat, water vapour and the Sun, to name just a few. The Sun is an object of which we still have much to learn. New data is continually being acquired so we can better understand how the Sun impacts our planet.

The Sun is the source of all energy on Earth. Without the heat it provides there would be no wind or clouds, no rain or rivers. It is natural to assume that changes in the energy arriving from the Sun will drive climate change. The Sun had been a main player in changes to the climate until James Watt’s steam engine was set to work in Britain’s textile factories in the 18th century. Since then temperature records have shown a rapid increase in line with the growth of human civilization. How the temperature will change over the next century is the focus of much research.

It is known that the Sun gets brighter over an 11-year “solar cycle” and manifests this change, counter-intuitively, with dark blemishes on its surface: sunspots (see Fig. 1). Indeed a sixty-year sunspot drought has been linked to the little ice age of the 17th century when fairs were held on a frozen river Thames. The Sun has been brighter and covered in more sunspots than usual over the past century and is now returning to a quieter state. Climate records agree. Since the beginning of the 21st century, global temperature rises have levelled off, though they are still some of the highest ever recorded.

So, to what degree does the Sun influence the climate? To answer this the Sun must be understood in great detail. Knowing the total energy output of the Sun is one facet of the investigation, but that is not enough to account for all the variation observed on Earth. When you break the “total” energy down into its spectrum of constituent parts – just like creating a rainbow with a prism – solar researchers have found that each part varies by different amounts. Atmospheric scientists know that different kinds of light reach different depths in our atmosphere and so drive chemical reactions and winds in different ways. To round off the problem, the Sun does not just vary over 11 years, but over centuries and millennia.

Scientists have been observing sunspots as an indicator of changes in the Sun for centuries, but the only part of the spectrum that has been well-isolated is the ultra-violet portion – the invisible region beyond blue – and only then for less than four decades. However, research into the ultra-violet region has led to some interesting discoveries. Research has revealed that the period of cold weather back in the 17th century may not have been a global cooling [1]. Instead it was likely an effect isolated to Europe and was the outcome of redirected weather patterns nudged by a change to the Sun’s ultra-violet output. Such localised behaviour as connected to one part of the Sun’s spectrum tells us how complex climate is.

Continuous observations of other regions of the Sun’s spectrum, the visible colours and the infra-red ‘heat’, only began last decade. This means there is very much less data over just a fraction of a solar cycle with which to draw conclusions and make predictions. Work is now being done to address these unknown facets of the Sun so that we better understand its influence on the Earth.

There is still a lot to learn. The Sun must influence climate globally, and likely in complex ways on a regional level. However, the evidence is undeniable that the Sun is not the cause of current global warming. The research underway into spectral changes of the Sun will lead to a deeper understanding of both how the Sun works and the effect it has on localised weather patterns and the climate as a whole. Ultimately, scientists will be able to aim the dart at the board more precisely as our understanding deepens of how the Sun varies.

[1] M. Lockwood, R. G. Harrison, T. Woollings and S. K. Solanki (2010): Are cold winters in Europe associated with low solar activity? Environmental Research Letters, doi:10.1088/1748-9326/5/2/024001


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Will Ball

I am a PostDoc at Physikalisch-Meteorologische Observatorium Davos (PMOD) World Radiation Centre in Davos, Switzerland. My research interests lie in two main areas: total and spectral solar irradiance variability, on all timescales from the solar rotation to millenia; and variability in the Earth's stratosphere, in particular the Sun's influence on stratospheric ozone and temperature and understanding how that may influence our weather and climate.
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