Developed and developing world responsibilities for historical climate change and CO2 mitigation

Abstract

At the United Nations Framework Convention on Climate Change Conference in Cancun, in November 2010, the Heads of State reached an agreement on the aim of limiting the global temperature rise to 2 °C relative to preindustrial levels. They recognized that long-term future warming is primarily constrained by cumulative anthropogenic greenhouse gas emissions, that deep cuts in global emissions are required, and that action based on equity must be taken to meet this objective. However, negotiations on emission reduction among countries are increasingly fraught with difficulty, partly because of arguments about the responsibility for the ongoing temperature rise. Simulations with two earth-system models (NCAR/CESM and BNU-ESM) demonstrate that developed countries had contributed about 60-80%, developing countries about 20-40%, to the global temperature rise, upper ocean warming, and sea-ice reduction by 2005. Enacting pledges made at Cancun with continuation to 2100 leads to a reduction in global temperature rise relative to business as usual with a 1/3-2/3 (CESM 33-67%, BNU-ESM 35-65%) contribution from developed and developing countries, respectively. To prevent a temperature rise by 2 °C or more in 2100, it is necessary to fill the gap with more ambitious mitigation efforts.

Fig. 1.

CO₂ concentration and air temperature in three historical experiments simulated by two earth-system models (Left: CESM; Right: BNU-ESM). Top: Observed (black, supplied by CMIP5) and modeled time series of annual CO₂ concentration from ALL (red, historical emission), AX1 (blue, developed world emissions only), and NX1 (green, developing world emissions only). Middle: Annual radiative forcing for the three experiments. Bottom: Five-year running averaged global mean air temperature anomaly relative to 1850–1869 with shading showing the range of values from 10 models’ CMIP5 14 esm-historical experiments. The models are BCC-ESM, BNU-ESM, CanESM2, CESM1_0_2, inmcm4, GFDL-ESM-2M, GFDL-ESM-2G, HadGEM2-ES, MIROC-ESM, and MPI-ESM-LR. The black line is the observed air temperature from HadCRUT3v (31).

Fig. 2.

Modeled centennial linear-trend patterns of air temperature (panels A and C, units: °C/100 y) and ocean temperature (panels B and D, units: °C/100 y) from 1906 to 2005 by the CESM and BNU-ESM model. Experiments used are labeled ALL (historical emissions), AX1 (developed world emissions only), and NX1 (developing world emissions only).

Fig. 3.

CO₂ concentration and simulated air temperature in four future experiments simulated by two earth-system models. Top: Observed and predicted atmospheric CO₂ concentrations. The black line is the observed CO₂ concentration, which is supplied by CMIP5. The other real lines indicate four future scenarios. They are labeled ABNB (all countries follow business as usual), ACNB (developed countries follow Cancun pledges while developing world pursues business as usual), ABNC (developing countries follow Cancun pledges while developed world does not), and ACNC (all countries follow their Cancun pledges). The broken lines come from the latest representative concentration pathways (RCPs) (13). Middle: Air temperature anomalies (relative to 1850–1869, five-year running averaged field) simulated by CESM combining historical simulation and four future scenarios. The observed (gray line) is from HadCRUT3v (31). Bottom: same as middle, but based on simulations by BNU-ESM.