Setting cumulative emissions targets to reduce the risk of dangerous climate change

Abstract

Avoiding ''dangerous anthropogenic interference with the climate system'' requires stabilization of atmospheric greenhouse gas concentrations and substantial reductions in anthropogenic emissions. Here, we present an inverse approach to coupled climatecarbon cycle modeling, which allows us to estimate the probability that any given level of carbon dioxide (CO 2) emissions will exceed specified long-term global mean temperature targets for ''dangerous anthropogenic interference,'' taking into consideration uncertainties in climate sensitivity and the carbon cycle response to climate change. We show that to stabilize global mean temperature increase at 2°C above preindustrial levels with a probability of at least 0.66, cumulative CO 2 emissions from 2000 to 2500 must not exceed a median estimate of 590 petagrams of carbon (PgC) (range, 200 to 950 PgC). If the 2°C temperature stabilization target is to be met with a probability of at least 0.9, median total allowable CO 2 emissions are 170 PgC (range, ؊220 to 700 PgC). Furthermore, these estimates of cumulative CO 2 emissions, compatible with a specified temperature stabilization target, are independent of the path taken to stabilization. Our analysis therefore supports an international policy framework aimed at avoiding dangerous anthropogenic interference formulated on the basis of total allowable greenhouse gas emissions.climate carbon cycle feedbacks ͉ cumulative emissions budget ͉ dangerous anthropogenic interference ͉ uncertainty analysis ͉ 2°C target

The Origin and Limits of the Near Proportionality between Climate Warming and Cumulative CO2 Emissions

“…Forcing from non-CO 2 greenhouse gases, sulfate aerosols, land-use changes, and volcanic events were set to their preindustrial averages throughout these simulations. To explore the effect of carbon cycle feedback strength on the TCRE, the climate sensitivity of the UVic ESCM (to a doubling of CO 2 concentration) was varied to 2.08, 3.28, and 4.58C, following the method of Zickfeld et al (2009). This method takes advantage of the simplified atmospheric model component such that outgoing longwave radiation to space is altered as a function of the change in global mean surface temperature to emulate variable strength of the physical climate feedbacks.…”

“…Given that Earth system models expect TCRE to be nearly constant until ]. The most intuitive suspect for that changing factor is the airborne fraction a, which, in models, is known to increase as cumulative carbon emissions rise (e.g., Zickfeld et al 2013). Results from the linear emissions experiments performed with the UVic ESCM help illuminate this problem.…”

“…A relationship that Earth system models suggest will hold until approximately 2000 Pg of carbon (Pg C) have been emitted to the atmosphere (e.g., Matthews et al 2009;Allen et al 2009;Zickfeld et al 2012;Gillett et al 2013;Allen and Stocker 2014). This linear relationship, the slope of which has been designated the transient climate response to cumulative CO 2 emissions (TCRE; Collins et al 2013;Planton 2013), is a highly convenient metric for climate policy, as it establishes a simple relationship between the cause of warming (CO 2 emissions) and the expected magnitude of warming that is independent of when carbon is emitted (e.g., Matthews et al 2009;Allen et al 2009;Zickfeld et al 2012;Gillett et al 2013;Allen and Stocker 2014). In addition, the rate independence of warming (implicit in TCRE) allows for simple path-independent budgets of cumulative carbon emissions to be established for the climate system to stay below a chosen threshold of warming.…”

The future of oil supply

“…A growing body of evidence indicates that global temperature change is approximately linearly related to cumulative carbon dioxide emissions and largely independent of the pattern of emissions over time [78][79][80][81][82]. Several modelling studies suggest that the most probable cumulative emissions for an average global temperature increase of 2 • C is around 1100 GtC, with a 5-95% uncertainty range of 1-2.5 • C per 1000 GtC [80].…”

Cumulative carbon emissions, emissions floors and short-term rates of warming: implications for policy

“…Rather, once temperatures have peaked, they would remain almost steady [8][9][10]. Several recent studies have sought to exploit this observation in order to provide a simple link between levels of cumulative emissions and future warming [11][12][13][14].…”