How do carbon cycle uncertainties affect IPCC temperature projections?

Abstract

Carbon cycle uncertainties associated with the Intergovernmental Panel on Climate Change temperature-change projections were treated differently between the Fourth and Fifth Assessment Reports as the latter focused on concentration-rather than emission-driven experiments. Carbon cycle feedbacks then relate to the emissions consistent with a particular concentration. A valuable alternative is to include all uncertainties in a single step from emissions to temperatures. We use a simple climate model with an observationally constrained parameter distribution to explore the carbon cycle and temperature-change projections, simulating the emission-driven Representative Concentration Pathways. The resulting range of uncertainty is a somewhat wider and asymmetric likely range (biased high).

Variations in the probability distribution function of air temperature anomalies in winter and summer from 1961 to 2016 over China

“…In light of the current global warming scenarios, it is predicted that extreme weather events will occur more frequently, which has attracted increasing attention from both scientists and the public (Parmesan et al ., 2000; Zhai and Pan, 2003; Alexander et al ., 2006; Donat and Alexander, 2012). The fact that the climate on Earth is becoming more and more extreme was also widely documented in the special report of the Intergovernmental Panel on Climate Change (IPCC) (Kharin et al ., 2007; Wu et al ., 2013; Bodman et al ., 2016; Pfleiderer et al ., 2019).…”

Changes of temperature and precipitation extremes in a typical arid and semiarid zone: Observations and multi‐model ensemble projections

“…The five models are selected because they can meet the data requirement and can be applied in climate extrems with feasibility and variability in China (You et al, ; Wang et al, ). By 2100, the concentration of CO 2 is ~550 ppm for RCP4.5 and 950 ppm for RCP8.5, representing a medium emissions scenario and a high emissions scenario in the future, respectively (Ricke et al, ; Bodman et al, ). And 27 extreme indices for 79 stations by historical, RCP4.5 and RCP8.5 scenarios can be calculated and analysed.…”

“…(You et al, 2017;Wang et al, 2017b). By 2100, the concentration of CO 2 is~550 ppm for RCP4.5 and 950 ppm for RCP8.5, representing a medium emissions scenario and a high emissions scenario in the future, respectively (Ricke et al, 2013;Bodman et al, 2016). And 27 extreme indices for 79 stations by historical, RCP4.5 and RCP8.5 scenarios can be calculated and analysed.…”

Reply on RC1

“…However, the dominance of concentration-driven scenarios means that CMIP6 does not contain self-consistent simulations of mitigation strategy and their climate outcome in Earth System Models. As a result, though IAM simulations already frame scenarios in terms of emissions pathways (Sognnaes et al 2021), the simplified internal representation of climate and carbon processes does not allow for a comprehensive assessment of the underlying carbon cycle uncertainties associated with the scenario tradeoffs, generally relying on simple climate models to represent uncertainty in carbon-climate feedbacks (Nauels et al 2017;Bodman, Rayner, and Jones 2016;Damon Matthews et al 2021 while this approach is convenient, bypassing process-resolving carbon cycle uncertainty in the assessment of mitigation strategy outcome has risks. A CMIP ensemble with a primary focus on emissions-driven scenarios, starting with CO2 emissions in CMIP7 but with a longer term objective to represent human activity through diverse emissions or land management, would allow ESM scenarios to represent real-world climate policy and its outcomes.…”