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Breaking away from the utopian assumption that the international community will agree on a single emissions allocation scheme, this study assesses approaches to setting country-level mitigation targets in line with the 2 °C goal.

Current national emissions targets can't limit global warming to 2 °C, calculate Joeri Rogelj, Malte Meinshausen and colleagues — they might even lock the world into exceeding 3 °C warming.

Emissions targets must be placed in the context of a cumulative carbon budget if we are to avoid dangerous climate change.

The effect of a cumulative emission of carbon on peak global mean surface temperature is better constrained than the effect of stabilizing the atmospheric composition. The approach is also insensitive to the timing or peak rate of emissions. Using carbon cycle models, it is shown that a trillion tonnes of carbon emissions (about half of which has already been emitted since industrialization began) will produce a most likely peak warming of 2 degrees Celsius.

The pledges put forward by each country to meet the goals of the Paris Agreement are ambiguous. Rogeljet al. quantify the uncertainty arising from the interpretation of these pledges and find that by 2030 global emissions can vary by −10% to +20% around their median estimate of 52 GtCO₂e yr⁻¹.

The politically defined threshold of dangerous climate change is an increase of 2 degrees Celsius in the mean global temperature. Simulations here show that when carbon dioxide and a full suite of positive and negative radiative forcings are considered, total emissions from 2000 to 2050 of about 1,400 gigatonnes of carbon dioxide yield a 50% probability of exceeding this threshold by the end of the twenty-first century. 'Business as usual' emissions will probably meet or exceed this 50% probability.

National targets give virtually no chance of constraining warming to 2 °C and no chance of protecting coral reefs.

If all new and updated national climate change mitigation pledges stemming from the Paris Agreement are implemented in full and on time, then 21st-century warming could be limited to just below 2 degrees Celsius.

Private-investor approaches for measuring the emissions associated with lending to governments risk creating perverse incentives.

Aiming for declining global temperatures can limit long-term climate risks compared with a mere stabilization of global warming, including sea-level rise and cryosphere changes.

Modelling that integrates the effects of uncertainties in relevant geophysical, technological, social and political factors on the cost of keeping transient global temperature increase to below certain limits shows that political choices have the greatest effect on the cost distribution.

The ‘pathway’ the world needs to follow to limit global temperature rise to 2 °C remains uncertain. Analysis that takes technical and economic constraints on reducing emissions into account indicates that emissions need to peak in the next decade and then fall rapidly to have a good chance of achieving this goal.

Models and scenarios on which climate projection are based vary between IPCC reports. To facilitate meaningful comparison, this study provides probabilistic climate projections for different scenarios in a single consistent framework, incorporating the overall consensus understanding of the uncertainty in climate sensitivity, and constrained by the observed historical warming.

Including passive CO₂ uptake as an anthropogenic removal in greenhouse gas accounting systems could undermine the Paris Agreement; measures to address this include acknowledging the need for Geological Net Zero and disaggregated accounting for carbon sinks.

Here the authors present a framework to assess the temperature outcomes of decarbonization scenarios from institutions such as the IEA, BP and Shell. Scenarios are evaluated for consistency with the long-term temperature goal of the Paris Agreement.

Current emissions scenarios include pathways that overshoot the temperature goals set out in the Paris Agreement and rely on future net negative emissions. Limiting overshoot would require near-term investment but would result in longer-term economic benefit.

Fundamental value judgments about acceptable maximum levels of climate change and future reliance on controversial technologies can be made explicitly in climate scenarios, thereby addressing the intergenerational bias present in the scenario literature.

The Paris Agreement includes bottom-up pledges and top-down warming threshold. Under this setting where countries effectively choose their own fairness principle, this article assesses the global warming implied by each Nationally Determined Contribution to inform the future ratcheting-up process.

Five equitable approaches to mitigation are investigated: the authors find that most developing countries are more ambitious than the average, whilst if developed nations and China adopted the average of the approaches the gap between INDCs and a 2 °C pathway would narrow.

Discrepancies exist between data used in countries’ greenhouse gas inventories and modelled benchmarks for the Paris agreement, according to an analysis of countries’ land-based greenhouse gas targets.

Uncertainties and subjective choices affecting remaining carbon budgets should be fully considered when applying them to international and national climate policies.

Warming is altering subtropical precipitation; however, it is not clear whether this will continue in an equilibrium climate. Using projections to 2300, Southern Hemisphere drying is shown to be a transient response to the meridional temperature gradient changes.

The objective of the Paris climate agreement is to limit global-average temperature increase to well below 2 degrees Celsius above pre-industrial levels and to further pursue limiting it to 1.5 degrees Celsius; here, the adequacy of the national plans submitted in preparation for this agreement is assessed, and it is concluded that substantial enhancement or over-delivery on these plans is required to have a reasonable chance of achieving the Paris climate objective.