The Science of Modern Climate Change

Modern climate change differs from natural climate change — also known as geologic climate change — because it is caused by humans and is occurring much faster than geologic climate change. Modern climate change is primarily driven by the effects of greenhouse gases, and is directly linked with human activities. Because modern climate change is occurring at a more rapid pace than geologic climate change, many animals, plants, and human communities are struggling to adapt.

The Greenhouse Effect

When the sun heats the Earth, some of that heat is naturally released back into space. When that excess heat is trapped by the atmosphere, that is known as the greenhouse effect. This is a natural process. By trapping some of the sun’s warmth, our atmosphere keeps the Earth at a livable temperature. Without the greenhouse effect, the Earth would not be able to support life as we know it.

Earth’s climatic system has been relatively balanced, with CO₂ concentrations of about 289 parts per million (ppm) for thousands of years. Since the Industrial Revolution, however, carbon emissions began to rise quickly due to combustion of fossil fuels and accelerated land use changed. In January 2015, the concentration of CO₂ in Earth’s atmosphere exceeded 400 ppm. With higher CO₂ concentrations come expectations of a stronger greenhouse effect and therefore warmer global temperatures.

Carbon dioxide, methane and other heat-trapping gases are known as greenhouse gases, because they contribute to the greenhouse effect. Learn more about carbon dioxide, methane and the greenhouse effect.

Tipping Points and Feedback Loops

The impacts of climate change are extremely difficult to predict, partially because the global climate system includes a number of tipping points and feedback loops.

Tipping points — the point of no-return for a particular impact — may occur very quickly, for example. Imagine a glass of milk that is slowly tipped to the side. Each slight shift sideways has relatively little impact — the milk sloshes sideways in the glass, but does not spill — but the glass eventually reaches a tipping point, when the contents spill onto the table.

Feedback loops can either accelerate (positive feedback loops) or slow (negative feedback loops) climate change. For example, warmer temperatures have caused Arctic sea ice to melt earlier in the season. Without that bright, reflective surface, the Arctic Ocean absorbs more solar heat than it previously did. This solar heat warms the water even more, and melts additional ice. This would be considered a positive feedback loop. Further, the chemical equilibrium of the Earth’s carbon cycle will shift in response to anthropogenic carbon dioxide (CO2) emissions. The primary driver of this is the ocean, which absorbs anthropogenic CO2 via the so-called solubility pump. At present this accounts for only about one third of the current emissions, but ultimately most (~75%) of the CO2 emitted by human activities will dissolve in the ocean over a period of centuries. However, the rate at which the ocean will take it up in the future is less certain.

Learn more about tipping points and feedback loops, and how both may affect the speed and intensity of climate change.