Paleoclimate Research Suggests CO2 target ‘not safe’
An analysis of geological records that preserve details of the last known period of global warming has revealed ‘startling’ results which suggest current targets for limiting climate change are unsafe.
The study by climate change experts at the University of Exeter has important implications for international negotiators aiming to agree binding targets for future greenhouse gas emission targets.
Professor Chris Turney and Dr Richard Jones, both from the University’s Department of Geography, have reported a comprehensive study of the Last Interglacial, a period of warming some 125,000 years ago, in the latest issue of the Journal of Quaternary Science.
The results reveal the European Union target of limiting global temperature rise to less than 2°C above pre-industrial levels shouldn’t be considered ‘safe’.
From their analysis, the scientists found 263 estimates of the conditions when sediments and ice were laid down during the Last Interglacial, allowing them to reconstruct past temperatures around the globe. To compare the reconstructed estimates with today, they took the Last Interglacial values away from modern temperatures averaged over the period 1961 to 1990.
The results show temperatures appear to have been more than 5˚C warmer in polar regions while the tropics only warmed marginally; strikingly similar to recent trends. Not only this, but taken together, the world appears to have been some 1.9˚C warmer when compared to preindustrial temperatures. Critically, the warmer temperatures appear to have resulted in global sea levels some 6.6 to 9.4 metres higher than today, with a rate of rise of between 60 to 90 centimetres per decade — more than double that recently observed.
[Ed. note: I believe the “decade” is a typo and what was meant is “century”, as the current observed rate is around 30 cm per century, and double that would be 60 cm per century.]
The higher temperatures seen during the Last Interglacial are comparable to projections for the end of this century under the low emission scenarios contained within the recent Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).
Professor Turney said: “The results here are quite startling and, importantly, they suggest sea levels will rise significantly higher than anticipated and that stabilizing global average temperatures at 2˚C above pre-industrial levels may not be considered a ‘safe’ target as envisaged by the European Union and others. The inevitable conclusion is emission targets will have to be lowered further still.”
The actual journal article is here:
Prof Turney has a blog, and a recent entry covered this topic:
The most recent super-interglacial took place between 130,000 and 116,000 years ago and has a string of monickers around the world. A common title is the Last Interglacial but if you’re north European, you may have heard this period labelled the ‘Eemian’, in North America, the ‘Sangamonian’, in Russia, the ‘Mikulino’ … you get the idea. Regardless of its name, the crucial point is at this time, the amount of sun’s heat falling on the northern hemisphere was marginally higher at summertime than it is today and this appears to have triggered a cascade of changes that drove the planet to significantly warmer temperatures, with several major knock-on effects. We know, for instance, that at this time there was a dramatic decrease in polar sea ice coverage while large parts of the Antarctic and Greenland ice sheets melted.[…]
Since the 1970s, a number of efforts have been made in gauging the temperature of the Last Interglacial, some more comprehensive than others. When the often handful of numbers have been crunched, estimates have ranged from no significant difference to today, to global annual temperatures being warmer by more than 2˚C. This is a huge uncertainty, given the rise in sea level that we know took place at this time. To try and resolve this conundrum, Dr Richard Jones (a friend and colleague at the University of Exeter) and I looked at more than 450 reports on the Last Interglacial. We were particularly interested in attempts to reconstruct temperature at individual sites using known relationships between the makeup of natural archives and modern temperatures. From this analysis, we were fortunate to find 263 estimates of the conditions when sediments and ice were laid down during the Last Interglacial, allowing Richard and I to reconstruct past temperatures around the globe. To compare the reconstructed estimates with today, we took the Last Interglacial values away from modern temperatures averaged over the period 1961 to 1990. The results were startling and our findings have just been published in the Journal of Quaternary Science under the title ‘Does the Agulhas Current amplify global temperatures during super-interglacials?’. Temperatures appear to have been more than 5˚C warmer in polar regions while the tropics only warmed marginally; strikingly similar to recent trends. Not only this, but taken together, the world appears to have been some 1.5˚C warmer when compared to the 1961 to 1990 average. If we take into account the rise in temperature that has happened since industrialization, we find the Last Interglacial was around 1.9˚C warmer. Furthermore, this period also shows the warming in the Indian and Southern oceans took place before that of the northern hemisphere, suggesting these regions may cause further global warming beyond that directly forced by increasing greenhouse gas levels.
The upshot of all of this is that Prof. Turney as with Dr. Hansen at NASA and a host of others are pointing out that the last interglacial (“Eemian”) was only slightly warmer than today and that caused huge ice melts.
From the records of the past there is sufficient evidence to show that the Earth’s climate is highly sensitive to the changes of the scale that we humans are now undertaking.
We are already around .5C above the 1961-1990 baseline, which means we’ve only got about 1C more to go before the Earth’s surface temperature starts to be Eemian-like. Thus, we don’t have much margin to play with when it comes to further changes to the climate.