Like other stars, our Sun is a nuclear furnace which means its solar radiation (that warms the Earth) is constantly increasing. The Sun will die in about 5 billion years when it runs out of fuel (helium and hydrogen). The solar radiation increases about 1% every 100 million years and it is estimated that the Sun’s solar radiation has increased 37% since the birth of the planet. As the Sun’s radiation increases over time the Earth must constantly evolve in order to maintain a stable temperature for sustaining life. How has the Earth been able to maintain a stable temperature for life for over 3 billion years?
The Gaia Hypothesis proposed by James Lovelock and Lynn Margulis in 1974 is a theory that explains long-term climate stabilization. In this theory the Earth is a self-regulating system composed of physical, chemical and biological (including humans) components. This theory proposes that the biota (all living organisms) play an important role in maintaining a stable temperature for life. For example photosynthetic organisms extract carbon dioxide from the atmosphere and use sunlight to create organic matter (carbon-rich material that all organisms contain) followed by carbon burial of this organic matter in sediment on land and in the ocean (my posting entitled Carbon Cycle). The evolution of the biota and the environment are tightly coupled together as a single inseparable process. The biota evolves to counteract changes in the environment such as the increasing solar radiation the Earth receives from the Sun.
Physical factors like rock weathering are also involved in counteracting the increase in solar radiation. Through rock weathering, atmospheric carbon dioxide is converted to calcium carbonate and is eventually buried in the ocean floor (my posting entitled Carbon Cycle). Atmospheric carbon dioxide is also absorbed by the ocean and this carbon dioxide helps the ocean maintain a stable pH (my posting entitled Atmospheric Levels of Carbon Dioxide and Ocean Acidification). The Earth’s biota along with the ocean and the process of rock weathering are part of the planet’s natural, self-regulating system. They lower the atmospheric level of carbon dioxide to counteract the gradual increase in solar radiation and thus help maintain a stable temperature for life. This self-regulating system has been extremely effective for over three billion years. Life evolved as the environment underwent several glacial/interglacial 100,000 year cycles. The Milankovitch Cycles varied the Sun’s radiation from a low incidence during glacial periods to a high incidence during interglacial periods (my posting entitled Role of Milankovitch Cycles and Sunspots in Climate Change). Through the Earth’s self-regulating system the carbon dioxide levels during glacial periods were 190-200 ppm and about 280 ppm during interglacial periods. The combined effect of the Milankovitch Cycles and the removal of atmospheric carbon dioxide by the self-regulating system helped lower the global temperature to 48-50o F during glacial periods and raised the global temperature to about 60o F during interglacial periods. During these 100,000 year cycles some species adapted, others became extinct while new species evolved.
Anthropogenic forces (induced by humans) such as burning of carbon-based fossil fuels, deforestation and methane/nitrous oxide emissions from agriculture are placing a tremendous burden on the Earth’s ability to control the level of atmospheric carbon dioxide. Anthropogenic forces are creating an unnatural atmospheric carbon overload. The atmospheric carbon dioxide level in 2009 was 390 ppm (up 73% from preindustrial revolution levels). The current global warming trend is now occurring in decades while natural cycles take 100,000’s of years (my posting entitled Carbon Cycle). We do not know how the Earth’s self-regulating system will respond to this rapid temperature change but it most likely will have a negative impact on the climate and our way of life.