When I first started investigating climate change, I found the linked five-part 2011 article by Steve Brown in clarifying the limits and advantages of comparing the Eemian (LIG or MIS 5e) with the Holocene and future projections for the Anthropocene. While the article makes many different points, I like the conclusions of the fifth article the opines that: a. MIS 11 (the Holsteinian), with its relatively high climate sensitivity, may provide a better paleo-case to calibrate state-of-the-art climate models against, and that b. the current exceedingly high rate of radiative forcing is taking us collectively into uncharted waters w.r.t. future Earth System responses:
Title: "The Last Interglacial - An Analogue for the Future?" Part I
https://skepticalscience.com/LIG1-0706.htmlExtract: "The Last Interglacial, also known as the Eemian in Europe and broadly corresponding to the global interglacial record of Marine Isotope Stage 5e (MIS 5e), was a period with significantly higher temperatures in many parts of the Northern Hemisphere compared to the present day (IPCC AR4) and similar to some predictions for the next century by current research. The Last Interglacial offers several benefits for comparison with the present day in that continental configuration, flora and fauna are near identical to today, as well as being a recent enough period to provide a range of high-resolution palaeoenvironmental proxy indicators. The Last Interglacial was also a period with higher global sea-level and a corresponding reduction in ice sheet area and volume, which are consistent with IPCC predictions for responses to future global warming. The period also had an atmospheric CO2 level of up to 300 ppm; similar to the pre-industrial era."
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Title: "The Last Interglacial Part Two - Why was it so warm?"
https://skepticalscience.com/LIG2-1906.htmlExtract: "The most important terrestrial controls of climate relate to albedo effects and changes in land surface, which determine the reflectivity of the Earth and how much energy from the Sun can be absorbed. For example, reduction in ice-sheet extent can expose lower albedo soil, rock and vegetation, which enhances surface warming. There was less glacial ice on Earth during the Last Interglacial compared to the present day, which suggests a significant reduction in the size of the Greenland and Antarctic Ice Sheets (IPCC AR4). This would support the view that an increase in land area exhibiting a lower albedo might have played some part in increased warming during the Last Interglacial."
Title: "The Last Interglacial Part Three - Melting Ice and Rising Seas:
https://skepticalscience.com/LIG3-1207.htmlExtract: "Ocean circulation is pivotal in its role for transferring heat around the globe, as well as being a significant factor in regional climate and weather patterns. Did the large volume of cold freshwater that returned to the ocean from the melting ice sheets affect this circulation and influence changes to climate and weather patterns?"
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Title: "The Last Interglacial Part Four - Oceanic Influences"
https://skepticalscience.com/LIG4-3008.htmlExtract: "Surface freshwater plays an important role for ocean circulation by its influence on the formation of deep water masses. A stronger deep circulation may increase northward heat transport by the AMOC, while a weaker deep circulation may promote less northward heat transport (Born et al., 2009). Barreiro et al. (2008) found that northern Atlantic waters have freshened rapidly in the past few decades and heat transported northward by the thermohaline circulation has decreased. It's expected that this freshening could increase further through intensified high-latitiude precipitation and glacial melt-water related to global warming. Vellinga et al. (2008) examined various model results that attempt to quantify how the AMOC responds to different melt-water fluxes from Greenland. In one model a large enough flux, or rate of flow, of melt-water to shutdown the AMOC was created, which resulted in a cooling of surface air temperature in excess of 15oC over the Norwegian and Barents Seas, with a lesser degree of cooling over the whole hemisphere. Most models that investigate increasing greenhouse gas scenarios predict that the AMOC will slow down as a result of such forcing (Driesschaert et al., 2007; Meehl et al., 2007). However, other model results suggest that anthropogenic aerosols may have delayed a greenhouse gas induced weakening of the AMOC by reflecting inbound solar radiation and partially offsetting greenhouse gas warming."
Title: "The Last Interglacial Part Five - A Crystal Ball?"
https://skepticalscience.com/LIG5-1110.htmlExtract: "Comparing the influences on the Last Interglacial climate with those assumed in future climate projections is problematic owing to fundamental differences, especially orbital forcing, seasonal warming, and greenhouse gas concentrations. Palaeoclimate studies show that differences in the manner in which the Earth orbited the Sun during the Last Interglacial are sufficient to explain the higher temperatures over most parts of the Northern Hemisphere, particularly due to greater axial tilt and eccentricity compared with the present day orbital configuration. This greater axial tilt provided stronger insolation (solar heating) at high latitudes and weaker insolation at low latitudes. Perihelion, when the Earth is nearest the Sun, occurred during summer in the Northern Hemisphere, which amplified seasonal insolation, while perihelion occurs in winter during the present day.
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The difference in greenhouse gas concentration combined with significantly different orbital parameters and seasonal insolation may limit the validity of using the Last Interglacial as an analogue for predicted future changes to the climate system. The proxy coverage of the period in the Southern Hemisphere and large parts of the Northern Hemisphere is poor, giving a bias towards Europe and the North Atlantic region. The value of the Last Interglacial in aiding prediction of future climate change is restricted to mainly Europe and the North Atlantic. To improve our ability to predict the potential impacts of future climate change it is essential that the search for proxy data in new locations with a more comprehensive geographical spread are sought out in order to get a more global picture of ancient climate with better resolution.
Acknowledging the problems and benefits of using the Last Interglacial as an analogue for a future warming climate begs the question of whether there may be a more suitable analogue in the past. Loutre and Berger (2002) suggest that Marine Isotope Stage 11 (MIS 11) from 405 to 340 ka would make a better analogue for future climate than the Last Interglacial, due to it being a warmer interglacial period, but with an orbital insolation signal that correlates closely with the recent past and future, giving a much better comparison of orbital forcing. MIS 11 also appears to have been possibly the warmest and longest interglacial of the past 5 million years and had an extended period with little or no continental ice, which is projected to occur under some future global warming scenarios.
Because the observed and predicted rate of increase in greenhouse gas concentrations and global warming is faster than seems to have happened during the Last Interglacial may mean that we are heading into uncertain territory."