The Earth system in a warmer world
It is now entering the public consciousness that future warming, triggered by near-term anthropogenic greenhouse gas emissions, will last for many millennia, causing impacts large enough to warrant naming a new geologic epoch, the Anthropocene. It is nearly impossible to understand the scale of these long-term impacts based on the short history of human scientific observations. The only viable way to gain observational insight is to examine responses to long-term warming documented in the geologic record.
The past-climate record provides many examples of climate and environmental conditions for a planet warmer than preindustrial, and the dynamic pathways into and out of these warm planetary states. For example, states of planetary warming similar in scale to what is expected in the course of this century, and the multi-millennial effects of such warming, may be found in the Pleistocene events MIS5.5, MIS11, MIS19, and MIS31. Further back, the Pliocene warm period (3.29-2.97 Myr ago) illustrates a case of long-term warm conditions and their impact on the terrestrial and marine biosphere (possibly including CO2 fertilization and ocean acidification). While some warm intervals in the past appear to be associated with elevated CO2 concentrations, atmospheric CO2 is either not well constrained or likely similar to preindustrial levels for other events. There may be many pathways to the creation of warm global states, and this diversity of geological examples provides useful natural antecedents to better understand future impacts in response to human modifications of the Earth system.
The multitude of climatic and environmental information stored in natural climate archives (such as temperature, precipitation, greenhouse gas and aerosol concentrations, sea level, biome composition, etc), together with climate model results, allow us to draw a comprehensive picture of how climate, the environment, biogeochemical cycles as well as atmospheric and ocean circulation change in warmer worlds. Accordingly, the Integrative Activity "Warmer worlds" will assess the knowledge on these changes and the existence of planetary boundaries associated with extreme warmth and rapid warming in the past. Moreover, it will identify gaps in current research and make suggestions for the future research agenda.
The following cross-cutting questions should be addressed (this is not an exhaustive list):
- Climate with its impacts and feedbacks in past warmer interglacials: analogues for a warmer future? Among others, how can long-term changes in the past under different boundary conditions be used to constrain the fast present warming?
- Relationship between climate change and greenhouse gas concentrations (cause, effect, and feedback).
- Dynamics of change associated with warming – are there limits to the speed of warming?
- Were there global environmental "Tipping Points" associated with warming in the past? And how can these past tipping points inform us about possible near-term future tipping points? For example, irreversible loss of polar ice, positive carbon feedbacks etc.
- Variability and Extreme Events associated with warmer worlds.
An array of PAGES working groups that individually address particular focal points regarding warming and its impacts (for instance QUIGS, PlioVAR, PALSEA, OC3, DICE, Global Paleofire and former Sea Ice and future Holocene working groups) provide comprehensive expertise on the various aspects of climate and environmental changes mentioned above. "Warmer worlds" will tap this expertise by actively engaging these (and other) PAGES working groups into a coordinated activity in order to draw a comprehensive picture of climate and environmental conditions associated with past global warmth. This comprises the synthesis of observational evidence, model-data comparison, and the analysis of simulated mechanisms and feedbacks to study the applicability of past analogues for future warming.
To accomplish its objectives, "Warmer worlds" will organize dedicated workshops where members of all PAGES working groups will be invited to participate, with the intent of sharing progress and steering the ensemble of groups toward a coordinated assessment outcome. In addition, external expertise from Future Earth and the World Climate Research Programme (WCRP) will be invited to complement the PAGES working groups, to insure that the view emerging from study of the geologic past remains focused on issues relevant to Earth and humanity’s future.
Structure and people
"Warmer worlds" will be organized by co-chairs, elected by a steering committee, which will include at least one member of the leadership of the associated working groups. The co-chairs of the integrative activity will be accountable to keep the integrative activity on track. This integrative activity will in turn provide impetus to keep the individual working groups moving forward at an appropriate pace.
Some plausible initial products include:
- Review paper on climate and environmental changes during MIS5.5 (and potentially other warm interglacials such) and its implications for dynamics of future warming on the scale of 100’s to 1000’s of years (already planned in QUIGS).
- Review paper on climate and environmental changes during the Pliocene and its illustration of climates with substantially less polar ice than today.
- Review paper on abrupt climate change events and the risk of their occurrence in the near future.
Aug-Dec 2016: Establish literature database on MIS5.5 (and potentially other warm interglacials).
Dec 2016-Feb 2017: Workshop on MIS5.5 (about 50 people) (and potentially other warm interglacials).
May-Sep 2017: Review paper on MIS5.5 (and potentially other warm interglacials).
Dec 2017-Feb 2018: Workshop on past climate under elevated CO2.
May 2018-May 2019: Review paper on past climate under elevated CO2.
Dec 2018-Feb 2019: Workshop on rapid changes and their occurrence in warmer worlds.
May 2019–May 2020: Review paper on rapid changes and their occurrence in warmer worlds.