Global ChangeIntersection of Nature and Culture

What happened to sea level in the past when the planet warmed 1-2 degrees?

Sunday, December 20th, 2009

A powerful tool that scientists use to determine impacts of climate warming is historical records from ice cores, ocean and lake sediments, fossil reef terraces, and tree rings.   These records have helped us determine that we are in a current warm (interglacial) phase—called the Holocene— of the Pleistocene Ice Age, a period spanning the last 2 million years, when Northern Hemisphere ice sheets advanced and retreated more than a dozen times.

In this week’s issue of Nature (subscription required), Robert Kopp and colleagues examined¹ the previous warm interglacial phase, the Eemian, which happened about 125,000 years ago.  The historical records suggest that global temperature was about 1-2 degrees C warmer than today, and maybe as much as 3-6 degrees C warmer at the poles.

The question they asked was this:  How much did global sea level rise with the 1-2 degrees C  global warming in the Eemian?  Using the geological record to estimate past sea level changes, they came up with a startling answer:

• 95% chance that sea level was 6.6 meters (22 feet) higher than today
  
• 67% chance that it was 8 meters (26 feet) higher
• 33% chance it was 9.4 meters (31 feet) higher

It’s important to remind ourselves that a 1-2 degree global warming is not some kind of scientific doomsday prediction—it’s actually the lower end of warming scenarios, pushing the limit of what is technologically and politically achievable.  If we continue a business as usual scenario, IPCC models suggest a global average warming of 4 degrees C by 2100.

¹Kopp, R et al. (2009) Probabilistic assessment of sea level during the last interglacial stage. Nature 462: 863-868.

_____

Photo credit:  http://www.flickr.com/photos/softpixtechie/ / CC BY 2.0