15 research outputs found
An investigation into linearity with cumulative emissions of the climate and carbon cycle response in HadCM3LC
We investigate the extent to which global mean temperature, precipitation, and the carbon cycle are constrained by cumulative carbon emissions throughout four experiments with a fully coupled climate-carbon cycle model. The two paired experiments adopt contrasting, idealised approaches to climate change mitigation at different action points this century, with total emissions exceeding two trillion tonnes of carbon in the later pair. Their initially diverging cumulative emissions trajectories cross after several decades, before diverging again. We find that their global mean temperatures are, to first order, linear with cumulative emissions, though regional differences in temperature of up to 1.5K exist when cumulative emissions of each pair coincide. Interestingly, although the oceanic precipitation response scales with cumulative emissions, the global precipitation response does not, due to a decrease in precipitation over land above cumulative emissions of around one trillion tonnes of carbon (TtC). Most carbon fluxes and stores are less well constrained by cumulative emissions as they reach two trillion tonnes. The opposing mitigation approaches have different consequences for the Amazon rainforest, which affects the linearity with which the carbon cycle responds to cumulative emissions. Averaged over the two fixed-emissions experiments, the transient response to cumulative carbon emissions (TCRE) is 1.95 K TtC-1, at the upper end of the IPCC’s range of 0.8-2.5 K TtC-1
[Letter] Zero emission targets as long-term global goals for climate protection
Recently, assessments have robustly linked stabilization of global-mean temperature rise to the necessity of limiting the total amount of emitted carbon-dioxide (CO2). Halting global warming thus requires virtually zero annual CO2 emissions at some point. Policymakers have now incorporated this concept in the negotiating text for a new global climate agreement, but confusion remains about concepts like carbon neutrality, climate neutrality, full decarbonization, and net zero carbon or net zero greenhouse gas (GHG) emissions. Here we clarify these concepts, discuss their appropriateness to serve as a long-term global benchmark for achieving temperature targets, and provide a detailed quantification. We find that with current pledges and for a likely (>66%) chance of staying below 2 °C, the scenario literature suggests net zero CO2 emissions between 2060 and 2070, with net negative CO2 emissions thereafter. Because of residual non-CO2 emissions, net zero is always reached later for total GHG emissions than for CO2. Net zero emissions targets are a useful focal point for policy, linking a global temperature target and socio-economic pathways to a necessary long-term limit on cumulative CO2 emissions
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The impact of European legislative and technology measures to reduce air pollutants on air quality, human health and climate
European air quality legislation has reduced emissions of air pollutants across Europe since the 1970s,
affecting air quality, human health and regional climate. We used a coupled composition-climate
model to simulate the impacts of European air quality legislation and technology measures
implemented between 1970 and 2010. We contrast simulations using two emission scenarios; one
with actual emissions in 2010 and the other with emissions that would have occurred in 2010 in the
absence of technological improvements and end-of-pipe treatment measures in the energy, industrial
and road transport sectors. European emissions of sulphur dioxide, black carbon (BC) and organic
carbon in 2010 are 53%, 59% and 32% lower respectively compared to emissions that would have
occurred in 2010 in the absence of legislative and technology measures. These emission reductions
decreased simulated European annual mean concentrations of fine particulate matter(PM2.5) by 35%,
sulphate by 44%, BC by 56% and particulate organic matter by 23%. The reduction in PM2.5
concentrations is calculated to have prevented 80 000 (37 000–116 000, at 95% confidence intervals)
premature deaths annually across the European Union, resulting in a perceived financial benefit to
society of US$232 billion annually (1.4% of 2010 EU GDP). The reduction in aerosol concentrations
due to legislative and technology measures caused a positive change in the aerosol radiative effect at
the top of atmosphere, reduced atmospheric absorption and also increased the amount of solar
radiation incident at the surface over Europe. We used an energy budget approximation to estimate
that these changes in the radiative balance have increased European annual mean surface temperatures
and precipitation by 0.45 ± 0.11 °C and by 13 ± 0.8 mm yr−1 respectively. Our results show that the
implementation of European legislation and technological improvements to reduce the emission of
air pollutants has improved air quality and human health over Europe, as well as having an unintended
impact on the regional radiative balance and climate