Solar activity is at best responsible for a third of the rate of global warming

A new study tries to examine whether variations in solar radiation or man-made are the cause of climate change

The sun provides energy for all processes on Earth since life began, including an effect on the climate. The sun also provides an annual and seasonal influence and changes the character of each of the hemispheres, when their direction relative to it changes. Since the beginning of the industrial revolution, a new force has been added to assume a significant influence on the Earth's climate.

For the past 20-30 years, we believe that greenhouse gases have had a dominant effect on recent climate change," says Robert Callahan, a climatologist at the Goddard Space Flight Center in Maryland. During the last three decades, NASA scientists have studied the unique relationship between the sun and the earth using instruments in space such as the SORCE satellite (the Solar Radiation and Climate Experiment) and through them they have studied how much of the sun's energy illuminates the earth, and they have also studied what happens to energy This is after it penetrates through the atmosphere.

The amount of energy reaching the Earth's outer atmosphere is called the total solar energy. This amount changes over different periods of time, from seconds to hundreds of years due to changes in the activity of the sun. The sun has an 11 year cycle from storm to calm and back again. Solar activity often creates sunspots, dark areas on the sun's surface that are formed as a result of concentrated magnetic fields. The measured solar radiation rate is very large around the peak of the cycle, when the number of sunspots is large and the sun's activity is high, compared to the solar minimum, when the sun is quiet and usually there are no sunspots.

"The fluctuations in the solar cycle affect the average temperature of the Earth by 0.1 degrees Celsius, with the temperature being slightly higher during the solar maximum and cooler during the minimum," says Thomas Wood, a scientist who studies the sun at the University of Colorado at Boulder. "The sun is currently at its minimum, the next maximum is expected towards the year 2012."

Using Sources, the scientists learned that approximately 1,361 watts per square meter of solar radiation reach the Earth's outer atmosphere during quiet periods, but when the sun is active, another 1.3 watts of solar radiation per square meter (0.1 percent) is added. "This figure is important for models that try to estimate the human impact on climate change." Callahan said.

During the last century, the average temperature on Earth increased by about 0.6 degrees Celsius. Solar radiation is responsible for 0.15 degrees Celsius or about 25% of the total change, according to computer models published in 2004 by researcher David Ring of Goddard. The Earth's climate depends on the delicate balance between the incoming solar radiation, the outgoing thermal radiation and the composition of the Earth's atmosphere. Even a small change in these parameters can affect the climate. About 30% of the solar energy reaching the earth is returned to space. Clouds, atmospheric aerosols, snow, ice, sand, ocean surfaces and even rooftops play a role in reflecting the sun's rays. The remaining 70% of the energy is absorbed by the earth, the oceans and the atmosphere.

"The greenhouse gases trap about 40% of the outgoing thermal radiation emitted by the earth" says Wood. This disrupts the balance between incoming solar radiation and outgoing thermal radiation, which will cause the Earth to warm over the next century, and accelerate the melting of the ice caps at the poles, which in turn will cause sea levels to rise and increase the likelihood of violent weather events.

Non-human impacts on climate change. Before the industrial age, the sun and volcanic eruptions had the greatest influence on the Earth's climate. The earth warmed and cooled in cycles. Relatively cold periods were the ice ages, the last of which ended 11 thousand years ago.

"Currently, we are between two main ice ages, in the period known as the Holocene. Callahan says. "During the last decades we have moved to a climate influenced by man and some call it the Anthropocene. The main change in the Earth's climate is greatly influenced by human activity, something that has not happened in the past."

According to Doug Rabin, a solar physicist at Goddard, the Sun is relatively calm compared to other stars. "We don't know what the sun is going to do in the next few hundred years, but it is possible that it will be much more active and therefore have a greater influence on the Earth's climate."

Or it will be calmer and create a colder climate on Earth similar to what happened in the 17th century. Almost no sunspots were formed between the years 1650-1715. A long period of inactivity may also be responsible for the Little Ice Age that Europe experienced, and may also reflect irregular changes in solar output over hundreds of years. During this period the winters in Europe were longer and colder by about 1 degree Celsius on average compared to today.

Since then, there has been a slow but steady increase in solar activity. Only if we find a way to reduce the amount of greenhouse gases emitted such as the carbon dioxide produced by burning fossil fuels (oil, coal, gas). The influence of the sun is not expected to be central to climate change. However, the changes in solar radiation will continue to cause alternating warming and cooling on the scale of 0.1-0.2 degrees Celsius over many years.

Future measurements of solar radiation variability

Over the past thirty years, a suite of NASA and European Space Agency satellites have provided scientists with important multi-instrument measurements of total solar radiation. The device Total Irradiance Monitor or TIM for short was launched in 2003 as part of the SORCE mission and provided measurements with great accuracy. A second device of this type has already been built and will be integrated into the Glory spacecraft planned for launch in 2009. The satellite and instrument are expected to provide a 30-year record of solar radiation measurements reaching the Earth's atmosphere, to help researchers better understand the sun's direct and indirect effects on climate. GLORY will also collect data on aerosols, one of the lesser-known pieces of the climate puzzle.