Rising Seas and Declining Species

Oceans Away

Phytoplankton comprise the most level of the food chain in the oceans. Credit: The University of Liverpool

One of the most disturbing aspects of climate change is the impact on the oceans, which are a tremendous source of nutrients for life on land. Acidification, ice melt, and surface temperature increases are impacting sea life in a myriad of ways.

How much can the ecosystems take?

An editorial in the September 2010 edition of the journal Nature Geoscience points out that the oceans may be floundering at their most basic level of the food chain: phytoplankton. The microscopic, photosynthesizing basis of ocean life accounts for half the production of organic matter on Earth. One estimate, published in the August edition of Nature, indicates a 1 percent decline of the global median of phytoplankton, based on observations dating back to 1899, in eight out of 10 ocean regions due to sea temperature rise.

The reason? The editorial points out that with higher temperatures, the ocean becomes more stagnant. Less mixing of nutrient -rich deep water occurs, cutting off phytoplankton food supplies. With the concentrations of phytoplankton dropping, it’s easy to imagine what happens to the rest of the food chain.

A decade-long Census of Marine Life, put out by researchers from more than 80 nations, was released on Oct. 4 in London. It aims to create a “roll call” of species in 25 “biologically representative” regions, from polar waters to tropical seas, in an effort to get a handle on what’s left out there.

With phytoplankton declines and other climate related impacts forcing change on the sea of life, we’ll finally have a baseline to track where our oceans are headed. This information could be essential in understanding how changes in the oceans could affect the future habitability of our planet.

The seas are rising, but how much?

We know the seas are rising, but by how much? Photo: Franklin O’Donnell

As the mercury continues to rise, we all know that the sea level is also going up. But by how much? Scientists do the best they can to model the impacts, and based on that policy makers have come up with the 2 degree Celsius limit to how much hotter the Earth can get and still be in the safety zone.

But what if they’re wrong? A paper published in the September Journal of Quaternary Science synthesized ice, marine, and terrestrial data from the last interglacial event, some 125,000 years ago, which was mainly driven by orbital changes in the Earth.

University of Exeter geographers Chris Turney and Richard Jones came up with a revised estimate of average global temperatures of 1.9 degrees C warmer than pre-industrial levels, which resulted in a whopping sea level rise of 6.6 to 9.4 meters higher than today. That breaks down to about 60 to 90 centimeters per decade, double that observed in recent years.

Consider our current projection on a CO2 low emissions scenario and the comparison is startling. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change considers a 2 degree C temperature rise, resulting in a 0.18 to 0.38 meter sea level rise to be a best case scenario, and one increasingly unlikely given little attempt to curb the planet’s appetite for carbon. This estimate on sea level rise we know is low, since it excludes ice sheet flow due to the lack of data in published literature.

If the last interglacial is any indicator of what 2 degrees C gets us, we could be in for much higher seas than we ever imagined.

This story has been translated into Portuguese.