Is the sun causing global warming? 

CLAIM

The Sun is causing global warming and climate change. 

FACT

The Sun can influence Earth’s climate, but it isn’t responsible for the recent warming trend. No significant change in the Sun’s energy output has been witnessed since the 1970s but rapid global warming has been recorded during this same period which points to the fact that the Sun is not causing global warming and climate change. 

WHAT THEY SAY

The Sun is the reason behind climate change as solar activity is influencing the global climate by causing the world to get warmer.  They claim that heat energy in the form of radiation from the Sun is affecting the Earth’s atmosphere and this is leading to global warming and climate change. 

WHAT WE FOUND

The Sun is one of the biggest sources of energy in terms of planet Earth and naturally, it has a ‘strong’ influence on the climate of Earth. Thus many believe that it is but only ‘common sense that the Sun is causing temperatures to rise through the heat energy output to Earth which is leading to global warming. In fact, solar activity is often blamed as the reason behind global warming in many skeptical arguments against human-caused climate change by climate change deniers. 

MOVING IN OPPOSITE DIRECTIONS

A study comparing solar activity and climate over more than a thousand years of our past found that global temperatures are quite matching to solar activity during that period. The same study, but, also found that post-1975, global temperatures are on the rise while solar activity has shown no significant rise or a long-term trend, and “studies and climate simulations indicate a nonsolar origin of the most recent warming episode since about 1970.”

There was a slight rise in the incoming sunlight amount between the late 1800s and the mid-1900s. This according to the experts contributed a maximum of 0.1°C of the 1.0°C of warming observed since the pre-industrial era. But importantly, no net change as such in the energy output of the Sun has been observed after the late 1970s to the present. This period is the time when humanity has witnessed the most rapid rise in global warming. 

On the contrary, it has come to light that a slight cooling trend has been shown by the sun since 1960 ‘oppositely coinciding’ with the rapid rise in global temperatures during the same period. According to a study, an analysis of solar trends has revealed that the sun might have actually helped planet Earth in the form of a cooling influence in the last few decades. 

COOLING OF THE STRATOSPHERE 

If the Sun’s energy output would have been the reason behind global warming, it would have heated up all layers of the Earth’s atmosphere. Instead, what we are witnessing is warming at the surface near the lower layers of the atmosphere and cooling in the stratosphere (upper atmosphere). The Stratosphere is cooling due to the loss of the ozone layer (ozone depletion) caused by human-induced actions such as the emission of chlorofluorocarbons (CFCs). The stratospheric Ozone layer absorbs the ultraviolet rays from the sun and its depletion has lessened its ability to absorb that energy. It now passes on to lower layers of the atmosphere.

Satellites and observations clearly show warming in the lower atmosphere (troposphere) and cooling in the upper stratosphere (stratosphere). This correlates with the fact that greenhouse gases are trapping heat in the lower atmosphere leading to a rise in temperatures in the lower layer near the surface of the earth. 

The figure below gives us a clear picture of what has been happening since 1950. A clear cooling trend of the stratosphere is shown in the upper chart and the warming of the troposphere near the surface of the Earth is clearly seen in this chart: 

(Global lower stratosphere (top) and troposphere (bottom) temperatures between 1958 and 2012. Figure from the UK MET Office HadAT. Source: carbonbrief.org)

COSMIC RAYS?

The high-energy protons and atomic nuclei originating from the Sun and also from beyond our solar system are called Cosmic rays. Changes in solar activity lead to changes in the flow of these cosmic rays through Earth’s atmosphere. It has often been claimed that cosmic rays, by creating more ions, might modify cloud formation resulting in big changes in temperatures and climate. 

The effect of cosmic rays on cloud formation is not significant enough to have any impact on the Earth’s climate in a significant way. An IPCC report from 2013 stated, “Cosmic rays enhance new particle formation in the free troposphere, but the effect on the concentration of cloud condensation nuclei is too weak to have any detectable climatic influence during a solar cycle or over the last century.”

The fact that cosmic rays from the Sun are not the reason behind the unprecedented warming we have witnessed over the last few decades is well-established. It has been reported that the opposite might in fact be true as a rise in the amount of cosmic rays coming towards Earth might actually help in cooling the planet. 

HERE’S WHAT EXPERTS SAY

We reached out to our in-house expert, climate scientist, Dr Partha J Das. Here’s what he said on the topic:

“This is an old debate that was resorted to by some scientists to negate the human-induced climate change that we are observing now. However, there is growing evidence now that the observed climate change is being caused by anthropogenic factors, mainly increasing emissions of GHGs.”

“Climate change is not new. It has been a part of the earth’s planetary history for the last 4.2 billion years. It has seen several periods of extreme climate like the Ice Ages as well those with climatic optimum during which biological life was created and evolution of the same flourished. This refers to the natural climatic variability of the earth. Fluctuation of solar radiation entering the earth’s atmosphere is one of those few natural reasons that are responsible for this natural variability of the dynamic climate systems of the earth.”

“However, the present phase of climatic change is due to the enhanced greenhouse effect caused by excessive emission of greenhouse gases since the beginning of the industrial age in Europe. One of the strengths of the IPCC reports so far is that it has gathered enough scientific evidence that has established that the present climatic change is a consequence of human-induced activities, mainly the release of much more GHGs than the planet’s lower atmosphere used to hold for the last 800,000 years.”