The rise in global atmospheric CO2, surface temperature, and sea level from emissions traced to major carbon producers
Climatic Change Springer Nature 144:4 (2017) 579-590
Emission budgets and pathways consistent with limiting warming to 1.5 °C
Nature Geoscience Nature Publishing Group 10 (2017) 741-747
Abstract:
The Paris Agreement has opened debate on whether limiting warming to 1.5°C is compatible with current emission pledges and warming of about 0.9°C from the mid-19th-century to the present decade. We show that limiting cumulative post-2015 CO2 emissions to about 200 GtC would limit post-2015 warming to less than 0.6°C in 66% of Earth System Model members of the CMIP5 ensemble with no mitigation of other climate drivers, increasing to 240GtC with ambitious non-CO2 mitigation. We combine a simple climatecarbon- cycle model with estimated ranges for key climate system properties from the IPCC 5th Assessment Report. Assuming emissions peak and decline to below current levels by 2030 and continue thereafter on a much steeper decline, historically unprecedented but consistent with a standard ambitious mitigation scenario (RCP2.6), gives a likely range of peak warming of 1.2- 2.0°C above the mid-19th-century. If CO2 emissions are continuously adjusted over time to limit 2100 warming to 1.5°C, with ambitious non-CO2 mitigation, net future cumulative CO2 emissions are unlikely to prove less than 250 GtC and unlikely greater than 540GtC. Hence limiting warming to 1.5°C is not yet a geophysical impossibility, but likely requires delivery on strengthened pledges for 2030 followed by challengingly deep and rapid mitigation. Strengthening near-term emissions reductions would hedge against a high climate response or subsequent reduction-rates proving economically, technically or politically unfeasible.A modified impulse-response representation of the global near-surface air temperature and atmospheric concentration response to carbon dioxide emissions
Atmospheric Chemistry and Physics European Geosciences Union 17 (2017) 7213-7228
Abstract:
Projections of the response to anthropogenic emission scenarios, evaluation of some greenhouse gas metrics, and estimates of the social cost of carbon often require a simple model that links emissions of carbon dioxide (CO2) to atmospheric concentrations and global temperature changes. An essential requirement of such a model is to reproduce typical global surface temperature and atmospheric CO2 responses displayed by more complex Earth system models (ESMs) under a range of emission scenarios, as well as an ability to sample the range of ESM response in a transparent, accessible and reproducible form. Here we adapt the simple model of the Intergovernmental Panel on Climate Change 5th Assessment Report (IPCC AR5) to explicitly represent the state dependence of the CO2 airborne fraction. Our adapted model (FAIR) reproduces the range of behaviour shown in full and intermediate complexity ESMs under several idealised carbon pulse and exponential concentration increase experiments. We find that the inclusion of a linear increase in 100-year integrated airborne fraction with cumulative carbon uptake and global temperature change substantially improves the representation of the response of the climate system to CO2 on a range of timescales and under a range of experimental designs.Drivers of peak warming in a consumption-maximizing world
Nature Climate Change Springer Nature (2016)
Abstract:
Peak human-induced warming is primarily determined by cumulative CO2 emissions up to the time they are reduced to zero1,2,3. In an idealized economically optimal scenario4,5, warming continues until the social cost of carbon, which increases with both temperature and consumption because of greater willingness to pay for climate change avoidance in a prosperous world, exceeds the marginal cost of abatement at zero emissions, which is the cost of preventing, or recapturing, the last net tonne of CO2 emissions. Here I show that, under these conditions, peak warming is primarily determined by two quantities that are directly affected by near-term policy: the cost of ‘backstop’ mitigation measures available as temperatures approach their peak (those whose cost per tonne abated does not increase as emissions fall to zero); and the average carbon intensity of growth (the ratio between average emissions and the average rate of economic growth) between now and the time of peak warming. Backstop costs are particularly important at low peak warming levels. This highlights the importance of maintaining economic growth in a carbon-constrained world and reducing the cost of backstop measures, such as large-scale CO2 removal, in any ambitious consumption-maximizing strategy to limit peak warming.Human influence on climate in the 2014 southern England winter floods and their impacts
Nature Climate Change Nature Publishing Group 6 (2016) 627-634