Climate Change and Reciprocity
The Short Story
The atmospheric greenhouse effect keeps Earth warm. Carbon dioxide is a major contributor to this effect. Thus, increasing carbon dioxide in the atmosphere increases the greenhouse effect, which in turn warms Earth. Burning fossil fuels adds carbon dioxide to the atmosphere and, thus, via the greenhouse effect causes the planet to warm. Since the industrial revolution, Earth has warmed by 2 degrees Fahrenheit due to the burning of fossil fuels. Future burning of fossil fuels will continue to warm Earth, which will lead to the melting of more sea-ice and the Greenland and Antarctic ice sheets. Projected changes over the next 80 years will create major disruptions to life on Earth.
A Longer Explanation
The current warming of Earth is a direct result of human activity that is altering Earth’s greenhouse effect. The greenhouse effect is due to certain gases in the atmosphere that efficiently absorb heat (infrared) radiant energy emitted by Earth’s surface. All bodies emit heat and that includes Earth’s surface. Most of the gases that compose our atmosphere do not absorb much of the solar energy reaching us from the Sun. This solar energy travels through the atmosphere and warms the planets surface. You can experience this by lying on the ground on a sunny day. As the surface warms it emits radiant energy back towards the atmosphere. This emitted heat (infrared) energy eventually makes its way to outer space. For a stable climate system the amount of solar energy absorbed by the Earth system equals the amount of heat energy emitted to space. This balance of inflowing and outflowing energy determines the global temperature of the planet.
For over 150 years we have known that the primary gases in the atmosphere regulating the amount of heat energy escaping to space are water vapor and carbon dioxide with a few other gases playing a minor role. The interesting fact is that the concentration of these two gases in the atmosphere is quite small (less than a few hundredths of a percent). These very potent greenhouse gases essentially determine the planets temperature and lead to a planet hospitable to life.
We know that over many millions of years geologic processes have changed the amount of carbon dioxide in Earth’s atmosphere. When atmospheric carbon dioxide is high, the planet warms. When it is low, the planet cools. Thus, Earth’s deep history tells us that changes in atmospheric carbon dioxide regulate the planet’s temperature.
Ever since the Industrial revolution humans have altered this slow, geologic cycling of atmospheric carbon dioxide. Through the burning of fossil fuels (which are rich in carbon) we have increased the amount of carbon dioxide in the atmosphere by 43% since the early 1800s. This has led to an increase in the greenhouse effect, which, in turn, has caused the planet to warm by almost 2 degrees Fahrenheit.
If we continue to rely on fossil fuels as our major source of energy, then by 2100 we will have more than tripled the amount of carbon dioxide in the atmosphere since pre-Industrial times. Earth’s atmosphere has not contained this much carbon dioxide for at least 45 million years, which was a time of great warmth with no polar ice caps and very high sea levels.
It is important to realize the time scale of this change. Natural cycling of carbon dioxide takes hundreds of thousands to millions of years to occur. Human activity is dramatically increasing atmospheric carbon dioxide levels on time scales of decades to centuries. Earth’s biosphere is sensitive to how quickly change occurs for it must adapt to these changes. The more rapid the changes, the more difficult it is for life to adapt.
If we continue to increase carbon dioxide in the atmosphere, then within 80 years the planet will most likely warm by 6 degrees Fahrenheit. This may seem like a small number, but we are talking about a global average. Temperature changes at higher latitudes will be much greater than this. Six degrees is actually a very large warming compared to what we see from the historic and geologic record.
We are already witnessing the changes associated with global warming. Arctic sea ice has dramatically declined in the summer, Greenland and Antarctic ice sheets are melting, sea level is rising, snow cover over continents is declining, winter seasons are shortening, storms are becoming more intense, plants and animals are responding to the changes. Our oceans are also becoming more acidic due to the fact that one quarter of the emitted carbon dioxide from the burning of fossil fuels is taken up by the world’s oceans.
These changes will continue to increase and intensify into the future. An important aspect of global warming is time. The world’s oceans serve as the storage place for much of the additionally trapped energy (85%) from the increased greenhouse effect. The oceans hold heat for a long time. Think of how long a pot of hot boiling water stays hot even after you have turned off the heating element on your stove. Water has the capacity to store heat for a long time. Thus, we have already committed Earth to future change by adding energy to the oceans. If we were to magically fix the atmospheric concentration of carbon dioxide right now, the ocean surface will continue to warm because of this stored heat. It is estimated that there is an additional 1 degree Fahrenheit of warming already stored in the oceans. This is one reason we must act now to stop burning fossil fuels. The longer we use these fuels, the more heat we will be storing in the oceans. The other reason is that, as mentioned, Earth’s process to remove atmospheric carbon dioxide works very slowly. If we allow atmospheric carbon dioxide levels to increase over the next 80 years and then stopped using these fossil fuels, then it would take nature over 100,000 years to reduce the carbon dioxide back to pre-Industrial levels. This is the other reason we must transition off of fossil fuels as soon as possible. If we don’t, we are committing human society and all life on Earth to dramatic long-term environmental change.
The basic science of global warming is well understood. 97% of scientists agree that Earth is warming and the major cause for the warming is the burning of fossil fuels. The science of global warming was well established over one hundred years ago. Over the past century continuing scientific research has confirmed and strengthened our understanding of global warming. Our understanding of this problem is rooted in observations and basic physics and is incontrovertible.