Throughout history, the Earth’s climate has warmed and cooled in cycles because of changes in the Earth’s orbit, ocean currents, and other natural factors.

But since the 1970s, the global temperature in the air, the oceans, and on land has risen extremely quickly. Glaciers worldwide are retreating. And in the past ten years, sea levels have risen at twice the rate they did last century. Scientists say a natural cycle could not cause these dramatic changes.

Broccoli: “When we look back at records of climate, particularly long records of climate that have been reconstructed from things like tree rings, and ice cores, and coral reefs in the ocean, we see that the variability that has occurred in the past is too small to be responsible for the size of the change in climate that has occurred over the last several decades.”

That’s Dr. Anthony Broccoli of Rutgers University. He says computer models of the climate show that the observed rapid warming cannot be explained by natural causes alone.

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So climate scientists are confident humans have already caused global warming, and if we continue to release heat-trapping pollution, we’re on the path to an even hotter future.

Reporting credit: ChavoBart Digital Media.
Photo: Copyright protected.

More Resources
Causes of Climate Change
Global Temperature
Climate change: How do we know?
Natural Variability of Climate
Effects of Natural Variability
Long-term Natural Variability and 20th Century Climate Change

Bud Ward

Bud Ward is Editor of Yale Climate Connections. He started his environmental journalism career in 1974. He later served as Assistant Director of the U.S. Congress's National Commission on Air Quality,...