Intro to the Mid-Pliocene:
“During the Middle Pliocene, the Earth experienced greater global warmth compared with today, coupled with higher atmospheric CO2 concentrations. …In accordance with palaeobotanical data, all model simulations indicate a generally warmer and wetter climate, resulting in a northward shift of the taiga–tundra boundary and a spread of tropical savannahs and woodland in Africa and Australia at the expense of deserts… the Greenland ice sheet was reduced by at least 30%.” Climate and environment of a Pliocene warm world Salzmann et al, 2011
“The global average temperature in the mid-Pliocene (3.3 Ma–3 Ma) was 2–3 °C higher than today, global sea level 25m higher and the northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma. ” [Ma = a million years ago] Wikipedia/Pliocene Climate
“As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades.” Pliocene and Eocene provide best analogs for near-future climates Burke, Williams, et al (2018)
“…[During the mid-Pliocene Warming Period], trees remained a dominant feature of the landscape.” Regional climate and vegetation response to orbital forcing within the mid-Pliocene Warm Period: A study using HadCM3 Prescott, Dolan, et al (2018)
“Under RCP4.5 [a mid-range emissions scenario], climate stabilizes at Pliocene-like conditions by 2040 CE [Current Era].” Pliocene and Eocene provide best analogs for near-future climates Burke, Williams, et al (2018)
Short version: The mid-Pliocene climate may be a decent proxy for the earth’s near-future climate, under the mid-range emissions scenario Representative Concentration Pathway 4.5, otherwise know as RCP4.5, The mid-Pliocene was around three million years ago. The global climate was wetter and 2-3 °C higher than today. Atmospheric CO2 and sea levels were also higher. There was much less ice in the northern hemisphere. Forests, woodland and savanna dominated the landscape. Deserts shrank.
What is RCP4.5? Representative Concentration Pathways (RCPs) are time-dependent projections of Greenhouse Gas (GHG) concentrations in the upper atmosphere. The UN’s Intergovernmental Panel on Climate Change has focused on four RCPs and these are the ones typically used in climate models to gauge possible effects of climate change. The four RCPs are RCP2.6, RCP4.5, RCP6.0, and RCP8.5. The higher the number, the worse it gets. RCP8.5 is a worst-case “no-mitigation” scenario that assumes humanity does next to nothing to reduce GHG emissions. Apocalyptic visions of our planet’s future are often based on RCP8.5, along with the assumption that little will be done to build resilience to the changing climate. The Paris Agreement (an agreement within the United Nations Framework Convention on Climate Change) set the goal to keep emissions below RCP2.6 to limit warming to 1.5 °C above pre-industrial levels this century. I’m thinking RCP2.6 is too optimistic and RCP8.5 is too pessimistic. RCP4.5 seems just right. Here’s more on the RCPs and associated climate futures:
Per the above chart, RCP4.5 sees the climate stabilizing at around 3 °C above pre-industrial levels. Since the global climate is already 1 °C above pre-industrial, that would be 2 °C above where we’re at now. Looks like a mid-Pliocene world to me.
Yes, climate change is happening much more quickly than what happened during the mid-Pliocene. Then again, humans have many tools at their disposal to adapt to the change, from drought-resistant crops and the sustainable intensification of agriculture to coastal reinforcement, to habitat management to organized migration and more. It will be difficult but it won’t be an apocalypse.
Burke, K. D., J. W. Williams, et al. (2018). "Pliocene and Eocene provide best analogs for near-future climates." Proceedings of the National Academy of Sciences 115(52): 13288-13293. https://doi.org/10.1073/pnas.1809600115
Explainer: The high-emissions ‘RCP8.5’ global warming scenario Zeke Hausfather/Carbon Brief August 21, 2019
Prescott, C. L., A. M. Dolan, et al. (2018). "Regional climate and vegetation response to orbital forcing within the mid-Pliocene Warm Period: A study using HadCM3." Global and Planetary Change 161: 231-243. https://doi.org/10.1016/j.gloplacha.2017.12.015
Salzmann, Ulrich, Williams, Mark, Haywood, Alan, Johnson, Andrew, Kender, Sev and Zalasiewicz, Jan (2011) Climate and environment of a Pliocene warm world. Palaeogeography, Palaeoclimatology, Palaeoecology, 309 (1-2). pp. 1-8. ISSN 0031-0182 https://doi.org/10.1016/j.palaeo.2011.05.044