Why are temperatures lower in winter? Because the sun feels farther away and is unable to warm our skin, many assume that the sun is further away from the earth during the winter, but this is not the case for those of us who live in the northern hemisphere. On average, the earth is about 93 million miles away from its stellar solar source, and it takes about 8.33 minutes for sunlight escaping the sun to reach the earth’s surface. However, in January, sunlight reaches the earth a little earlier due to perihelion. On January 4, 2022, the earth will be only 91,406,842 miles (147,105,052 km) away from the sun, making it the closest it will be to the sun in the entire year of 2022. As the earth moves around the sun, it follows an elliptical orbit. The average distance from the earth to the sun during this annual journey is 93 million miles, but at perihelion it is about 1.4 million miles closer than average, causing sunlight to reach the earth about 9.65 seconds earlier.
Helios is the Greek name for the Sun, one of about 100 trillion stars in the Milky Way galaxy, and the most important star for us on Earth. The root word “peri” means close, so perihelion translates as “near the Sun”. Later the Romans replaced the word Helios with Sol, the Latin name for the Sun, the origin of words such as solar, solstice, and parasol. At perihelion the Earth is about 91.4 million miles away from the Sun, and at aphelion (ap = away) the Earth is about 3.1 million miles further away from the Sun. In 2022, aphelion is on July 4, when the Earth is 94,509,598 miles (152,098,454 km) away from the Sun, and in summer the Northern Hemisphere tilts towards the Sun, despite the greater distance.
In January, the Earth’s North Pole moves away from the Sun, causing people in the Northern Hemisphere to experience a lack of sunlight and mid-winter. The Southern Hemisphere is on average nearly 1.4 million miles away from the Sun, so it receives a concentrated amount of solar energy, resulting in higher insolation at southern latitudes. Notice that the blue line in the insolation vs. latitude graph has slightly higher average insolation than the red line. This is because the Earth is closer to the Sun during the Southern Hemisphere summer. Insolation is “incoming solar radiation” and can be measured at the top of the atmosphere and at the Earth’s surface, where we experience it as heat energy transferred to objects. That heat energy is absorbed, reflected, and dispersed by air, land, life, and water.
The Sun has the most important influence on Earth’s climate. If the Sun stopped shining tomorrow, weather and life processes would slowly and violently grind to a halt. Insolation plays a leading role in Earth’s temperature variations and is therefore one of the most important climate forcing variables (or climate drivers) of the Earth. As the amount of sunlight reaching the Earth’s surface changes over time, the temperature of the atmosphere and surface changes, and Earth’s systems adapt to the changing temperatures… and the sum of these countless changes is climate change. Insolation is constantly changing, and therefore the climate is constantly changing over decades, centuries, millennia, and millions of years. The map below is a net radiation map showing the variations in radiation/energy on Earth that affect climate.Click on the link to see a time-lapse map of radiation changes on Earth..
Climate is very complex and every aspect of nature influences it. Changes include solar activity (due to changes inside the sun), the rate of volcanic activity (due to changes inside the earth), the composition of the atmosphere (due to the addition and removal of elements to the atmosphere), the orbital patterns of the earth (Milankovitch cycles)… just to name a few. It is hard to find an aspect of nature in this small corner of the universe that does not directly or indirectly affect the climate of the earth. The only constant is change, as the climate is the sum of all natural processes that are constantly changing. Humans are part of the natural processes on earth and are now the main climate forcing variable. Human unchecked energy use is disrupting the normal climate change patterns by trapping more solar radiation.
today, The AnthropoceneThe Earth’s average atmospheric temperature is rising due to increasing concentrations of greenhouse gases produced by human activities. Greenhouse gases absorb infrared, i.e. heat energy. If you put on infrared goggles you would see sources of heat energy such as body heat and surfaces warmed by the sun. I often call greenhouse gases “heat gobblers” because they absorb the infrared/heat energy and keep it from escaping into space. In the future, we will see more heat being released due to increased solar radiation due to our orbital period (perihelion!) and increased solar output due to increased solar activity (Solar Cycle Bottom graph), much of the incoming solar radiation is retained in the Earth’s atmosphere because it is absorbed by greenhouse gases. The Sun is currently moving into a more active part of its solar cycle, resulting in a slow increase in insolation. Meanwhile, humans are emitting more and more greenhouse gases into the atmosphere.
The atmosphere and oceans absorb the extra heat, changing evaporation rates and weather patterns as aspects of the climate (i.e. nature) re-equilibrate to hotter temperatures. All of the natural cycles that influence climate change are still at work, and humans are disrupting the composition of the atmosphere and surface temperatures, changing the climate more dramatically and rapidly as it attempts to re-equilibrate to the increased heat retention.
2022 began with Earth relatively close to the Sun, which is why winter storms are raging in the Northern Hemisphere. We see that Earth’s atmosphere is warming, and deviations from once-normal weather patterns reflect a rapid process of climate re-equilibration. If humanity chooses to take responsibility for our role in Earth’s ever-changing climate, we can minimize the amount of re-equilibration the climate must undergo. We must foster equilibrium in perpetuity, recognizing that it takes time for the climate to re-equilibrate, and that while we cannot change the planet’s orbital period, the energy that comes from the Sun, or when major volcanic eruptions occur, we can change the impact we have on the climate, how we use energy, and how much pollution we emit. We can recognize that humanity has the power and choice to change the planet’s climate in ways that benefit life and human civilization. A species that travels space, cures diseases, makes pizza, and invents artificial intelligence certainly has the ability to wisely manage the Earth’s climate on which we depend.
