Coral Reefs Disappear as Climate Change Warms Greenhouse World

Coral reefs are the rainforests of the sea, containing a diverse range of species concentrated in one location. Fish use them for nurseries while people harvest them for their valuable resources. Now, researchers have taken a closer look at these reefs and have discovered that as the oceans change, these ecosystems may be in danger.

In order to get a better sense of how reefs may react in the future, the researchers took a look at what the oceans were like in the past. Our ancient seas experienced a greenhouse world about 50 million years ago. At that time, levels of greenhouse gases in the atmosphere were much higher than those that have been present during human history. For the past million years, for example, CO2 concentrations have never exceeded 280 parts per million; yet that may be changing. With industrialization, forest clearing and other activities, these gas levels are quickly rising. In fact, CO2 levels exceeded 400 parts per million for the first time in human history this past May.

In the greenhouse world, though, these concentrations were even higher. The gas levels reached between 800 to 1,000 parts per million and tropical ocean temperatures were as high as 95 degrees. Polar waters, in contrast, were a relatively balmy 53 degrees in comparison to today. If CO2 levels in our present world continue to rise, though, levels could exceed greenhouse world concentrations in just 80 years.

The scientists found that in the greenhouse world, a "reef gap" occurred between 42 and 57 million years ago. At that time, complex coral reefs disappeared and the seabed was instead dominated by piles of pebble-like single-celled organisms called foraminifera. In addition, large parts of the tropical and subtropical ocean ecosystems were supported by minute picoplankton instead of the larger diatoms found today. This means that it's likely that large marine animals such as tunas, whales and sharks wouldn't have been able to be supported.

"The tiny algae of the greenhouse world were just too small to support big animals," said Richard Norris, one of the researchers, in a news release. "It's like trying to keep lions happy on mice instead of antelope; lions can't get by on only tiny snacks."

The findings reveal that it's possible our warming world could spell drastic consequences for the world's reefs. While it's unlikely that we'll experience the same warming as during this greenhouse world, there still could be major complications. The scientists recommend a lowering of fossil fuel use in order to curtail the possibility of a greenhouse world occurring. Otherwise, we may be in for a very different Earth.

The findings are published in the journal Science.