Warming-level Dependent Characteristics of Human-Earth System Feedbacks
Characteristics of human-Earth system feedbacks vary at different warming levels
Background
The human and Earth systems are intricately linked: climate influences agricultural production, renewable energy potential, and water availability, for example, while anthropogenic emissions from industry and land use change alter temperature and precipitation. Such feedbacks have the potential to significantly alter future climate change. These feedbacks may also exert significant changes on 21st-century energy, agriculture, land use and carbon cycle projections, but little is known about their possible magnitudes, or about regional and sector dynamics under different forcing scenarios.
Objective
The goal of this research is to quantify and understand the implications of human-Earth system interactions for different regions and investigate the dynamics of these interactions at varying levels of warming.
Approach
Researchers used E3SM’s integrated Earth System Model (iESM) to run a set of simulations both with and without coupled feedbacks for medium and high radiative forcing (RF) scenarios with warming levels in 2100 of 4.5 W/m2 and 8.5 W/m2, respectively. E3SM’s iESM couples the Global Change Assessment Model (GCAM) – an Integrated Assessment Model (IAM) – to the Community Earth System Model (CESM). GCAM, like other IAMs, models the co-evolution of the economy, energy, and land systems. GCAM provides emissions and land use land cover change needed to force future changes in E3SM. The 8.5 W/m2 scenario includes continued growth in the economy, energy, and emissions, while the 4.5 W/m2 scenario uses a carbon price to incentivize the emissions reductions needed to keep radiative forcing to 4.5 W/m2 throughout the 21st century.
The iESM model features bidirectional information exchange between an economically-oriented integrated assessment model and the ESM. Scientists specifically examined the effect of changing land productivity on human systems, and the effect of changing land use/land cover and CO2 emissions on the Earth system.
Figure 1. The effect of human-Earth system feedbacks on temperature in the 4.5 W/m2 (left) and 8.5 W/m2 (right) warming level simulations. Figures show the difference between the coupled model runs and the uncoupled. Stippling indicates statistical significance.
Impact
The results of this study show that the effect of coupling differs across radiative forcing or warming levels and across regions, due to differences in the climate signal, human responses to those signals, and regional characteristics. The effect on global mean temperature is small, but there are larger effects on local temperature (see Fig. 1) some of which are statistically significant. Researchers found reductions in cropland area due to feedbacks in both the medium and high RF scenarios. In the medium RF scenario (4.5 W/m2) these reductions result in increased area for bioenergy and forests, leading to reduced energy system CO2 emissions, as the carbon price in this scenario incentivizes low carbon energy sources and terrestrial carbon storage. These incentives are absent in the high RF scenario (8.5 W/m2). These differences are key to understanding the possible future evolution pathways of the integrated Earth system in response to 21st century climate change. Additional models and hypothesis testing are needed to determine exactly when and how bidirectional feedbacks between human and Earth systems should be considered in future assessments.
Publication
Calvin, K., B. Bond-Lamberty, A. D. Jones, X. Shi, A. V. Di Vittorio, and P. E. Thornton, 2019: Characteristics of human-climate feedbacks differ at different radiative forcing levels. Glob. Planet. Change, 180, 126–135, https://doi.org/10.1016/j.gloplacha.2019.06.003.
Contact: Katherine Calvin, Pacific Northwest National Laboratory
Funding: U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.
