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The Earth's sixth mass extinction?

As human populations have grown and become more technologically advanced, we've taken a larger toll on the rest of the natural world. We've encroached on (and sometimes wiped out) the habitats of other species; we've released pollutants into the air, soil, fresh water, and oceans; and we've even changed the atmosphere and climate. These changes are beginning to disrupt Earth's systems at global scales — and are occurring rapidly. Because of our burning of fossil fuels, carbon dioxide levels are rising faster than they ever have at any point in Earth's history.10 It's no surprise then that extinction rates have risen substantially in the last 500 years.

Extinction rate
The graph at left shows that rates of bird extinctions have increased over time due to human impacts.11 The graph at right shows that if extinctions continue at high rates, we will have officially caused a mass extinction.12

In this module, we've seen that mass extinctions also involve a sharp increase in extinction rates over normal levels. So how bad is our current situation? Have humans pushed the Earth into its sixth mass extinction? The answer appears to be, "Not yet." But we are currently losing species at a rate far higher than normal background extinction rates, and the situation is dire. We are rapidly approaching a loss of diversity similar to that seen during mass extinctions. Biologists predict that unless we change course and begin preserving more species, within the next few hundred years, we will become the cause of Earth's sixth mass extinction.11

The good news is that we can stop this mass extinction. While there's no way to deflect an unforeseen asteroid strike or put a plug in a volcanic eruption, the current extinction rate is being pushed ever higher by human activity — and that means that human activity can also reverse this trend. We can reduce the extinction rate through policy changes that increase conservation efforts and curb our production of greenhouse gases to slow climate change. Studies of the Earth's history may play a surprisingly important role in this effort. If we can understand the chain of events that led to past mass extinctions, we will be in a better position to break that chain today. And if we can understand what traits make a species particularly vulnerable during a mass extinction, we may be able to better focus our conservation efforts. Investigating Earth's past extinctions may be one of the keys to preserving biodiversity for the future.


Want to learn more about how climate change affects life on Earth? Check out the following resources:


10Kiehl, J. 2011. Lessons from Earth's past. Science 331:158-159.

11Pimm, S., Raven, P., Peterson, A., Şekercioğlu, Ç. Ehrlich, P.R. (2006). Human impacts on the rates of recent, present, and future bird extinctions. Proceedings of the National Academy of Sciences USA. 103: 10941-10946.

12Barnosky, A.D., N. Matzke, S. Tomiya, G.O.U. Wogan, B. Swartz, T.B. Quental, … and E.A. Ferrer. 2011. Has the Earth's sixth mass extinction already arrived? Nature 471:51-57.

More details

Learn more about fossil fuels on the Understanding Global Change site.

Learn more about habitat loss on the Understanding Global Change site.

Learn more about pollutants and waste on the Understanding Global Change site.