Researchers publishing in Science have reported that sea surface temperatures during the last interglacial may have been no warmer than today.
Prof. Andrew Watson FRS, Royal Society Research Professor at the University of Exeter, said:
“This study indicates that, about 125 thousand years ago, global temperatures about the same as those today were associated with sea levels 6 to 10m higher. Sea level responds directly to global temperatures, but slowly, so that the full extent of sea level rise will only be apparent over thousands of years. The study suggests that in the long term, sea level will rise 6 metres at least in response to the warming we are causing. The good news is that with luck it will continue to rise slowly, so that we have time to adapt, but the bad news is that eventually all our present coastal city locations will be inundated.”
Dr Jeffrey Kargel, Department of Hydrology and Atmospheric Sciences at the University of Arizona, said:
“Jeremy Hoffman and others found that the global sea was about as warm during the last interglaciation epoch (129,000 to 116,000 years ago) as it is now. That was when sea levels ranged from 3 to 9.5 m (10 to 30 feet) higher than today’s oceans, according to Michael O’Leary of Manchester Metropolitan University and other researchers.
“One clear implication is that there is a lot of melting of glaciers and ice sheets still in store for Earth, even if temperatures could be magically stabilized. The retreat and thinning of mountain glaciers support this; it takes time for the ice to catch up with temperatures. Compounded with the problem that global temperatures are still zooming upward due to increasing burning of fossil fuels, and the implication is pretty clear that Earth will be losing a lot of ice mass, that sea level will be going up for many centuries to come. Our energy sources today are causing global disruption of climate and the effects are likely to be felt globally, continuously worsening for centuries and even thousands of years to come.
“Scientifically, the devil is in the details, and I find it fascinating that during the last interglaciation, the highest sea levels (most melting of ice) took place toward the end of that period according to work by O’Leary, whose group speculated that a critical ice sheet stability threshold had finally been crossed. Going from fascinating to worrisome, observations and models agree that big parts of the ice sheets in Antarctica appear already to have crossed such a critical threshold and have already begun to dump into the ocean, a process that will unfold over hundreds of years. I wonder what else is in store, considering that global temperatures continue to race upward.”
Prof. Eric Wolff FRS, Royal Society Research Professor at the University of Cambridge, said:
“The paper shows that globally, the last interglacial was no warmer than today. However, what really matters for sea level is the polar temperature, affecting ice sheets. Earlier work suggests that Antarctica and Greenland experienced warm temperatures similar to those they will be facing at the end of the century. That is worrying because sea level was several metres higher than it is today, implying that those conditions, if sustained for a long time, would be dangerous for ice sheets.”
Prof. Piers Forster, Director of the Priestley International Centre for Climate at the University of Leeds, said:
“The study greatly improves our estimate of past temperatures before the last ice age. This work is vital, as such good data from pre-history can be used to thoroughly test our climate models for a much wider set of conditions than they were built to simulate. A model that does well capturing such conditions likely has a good representation of underlying physical processes, making its predictions of future climate more trustworthy.”
Prof. Meric Srokosz, Marine Physics and Ocean Climate Scientist at the National Oceanography Centre (NOC), University of Southampton, said:
“This is an interesting study that shows that during the last interglaciation (129 to 116 thousand years ago) sea surface temperatures rose to be similar to those of today. The authors of this new study also note that during that period sea levels were 6 to 9m higher than the present day. Most significantly they show that the change in temperatures, which occurred over a long time scale (thousands of years) during the interglaciation, is occurring now over a much shorter time scale (a century). This demonstrates humanity’s rapid impact on the planet and raises the possibility of significant longer-term rises in sea level.”
Prof. Richard Allan, Professor of Climate Science at the University of Reading, said:
“The result that present global sea surface temperatures are indistinguishable from those at the last interglacial 125,000 years ago is extremely worrying since sea levels were 6 to 9 metres higher then compared to present.
“There are, however, considerable gaps and uncertainties associated with the indirect observations used in the study and at the last interglacial the Earth’s orbit around the sun was in a different configuration to today’s. Also, due to the length of time it takes to heat up the depths of our vast oceans and to melt giant ice sheets it would take thousands of years before sea level could potentially rise to such levels, so sustained and substantive cuts in greenhouse gas emissions from energy-intensive activities remain vital and beneficial to societies.
“The work further points out some interesting variations between ocean basins and discrepancies between simulations and observations of the last interglacial warm period. These discoveries offer a way to further improve the computer simulations that are pivotal in providing credible, physics-based projections of future climatic change and the resulting impacts on people and the ecosystems upon which we all depend.”
* ‘Regional and global sea-surface temperatures during the last interglaciation’ by Jeremy Hoffman et al. published in Science on Thursday 19 January 2017.