The annual ZERO IN reports by the CONSTRAIN project inform on crucial scientific elements relevant to the Paris Agreement in a timely manner, providing background and context on new developments that relate to the science-policy interface.

This first report zeroes in on the remaining carbon budget as well as on projected surface warming rates over the next 20 years. Both topics are crucially important when discussing the implementation of the Paris Agreement. Estimates for these quantities will be updated annually as part of the CONSTRAIN project.

Key findings

The remaining carbon budget

Different estimates and assessments of the remaining carbon budget in the recent scientific literature have caused some confusion. Building on the methodology used in the IPCC Special Report on Global Warming of 1.5°C, this report presents a robust framework reconciling different methodological choices and provides a single best estimate for a Paris Agreement compatible remaining carbon budget.
When using the carbon budget within climate policy, policy-makers need to be aware that it is a value judgement-dependent Earth system characteristic, that is, the concept combines science with value judgements. Value judgements around warming targets and respective probabilities of meeting them, for example, are important considerations for the carbon budget’s quantification and use.

Figure 2 scientific evidence vs value judgement graphic

From the start of 2020, the remaining carbon budget is 985 Gt CO2 for limiting warming to 2.0°C with a 66% probability. To limit warming to 1.5°C with a 50% probability, it is reduced to 395 Gt CO2, and 235 Gt CO2 for a 66% probability.

Decadal warming rates

If warming continues at its current rate, we are likely to reach 1.5°C between 2030 and mid-century. The rate depends on mitigation efforts, and would likely increase to unprecedented levels if the current Nationally Determined Contributions (NDCs) or stronger mitigation efforts are not delivered. This increase would reduce the timescales available for effective adaptation, in particular for the most vulnerable.
Conversely, stringent mitigation action could reduce the rate of human-induced near- term 2020-2040 warming by up to half. This underscores the benefits of near-term emission reductions including up to 2030, the timescale of the current NDCs.
Based on our present best scientific understanding, very high near-term warming rates – double or more of those observed in the recent past – are of low likelihood. However, this does not rule them out as a possibility, emphasising the need for urgent mitigation and action towards net zero emissions to contain this risk.

Publications

Climate Action Tracker: 2024 warming projection update

Despite an escalating climate crisis marked by unprecedented wildfires, storms, floods, and droughts, the Climate Action Tracker annual global temperature update shows global warming projections for 2100 are flatlining, with no improvement since 2021. The aggregate effect of current policies set the world on a path toward 2.7°C of warming.

Decarbonising light-duty vehicle road transport

The Climate Action Tracker provides updated 1.5ºC compatible benchmarks for the transport sector for the world as a whole and for seven individual countries; the US, EU, China, India, Brazil, South Africa and Indonesia.

Emissions Gap Report 2024: No more hot air … please!

The 2024 edition of UNEP’s Emissions Gap Report shows how much higher nations must aim. To get on a least-cost pathway for 1.5°C, emissions must fall 42 per cent by 2030, compared to 2019 levels. G20 nations, particularly the largest-emitting members, would need to do the heavy lifting.

The role of northern forests in limiting warming to 1.5°C

Northern forests are critical in the race to net zero CO₂ by mid-century. Protecting and restoring these forests, alongside steep and rapid reductions in fossil fuel emissions, is essential both to mitigating emissions and to supporting forest ecosystem services and biodiversity.

Methodology underpinning the State of Climate Action series: 2024 update

This technical note describes the State of Climate Action series’ methodology for identifying sectors that must transform, translating these transformations into global mitigation targets primarily for 2030, 2035 and 2050 and selecting indicators with datasets to monitor annual change. It also outlines the report’s approach for assessing progress made toward near-term targets and comparing trends over time.

Rapid urbanisation and climate change key drivers of dramatic flood impacts in Nepal

New study finds the devastating floods in Nepal late September were exacerbated by rapid urbanisation and climate change. The analysis found the relentless rain, which fell on saturated ground in the late monsoon, was made at least 10% heavier and 70% more likely by climate change.

LNG shipbuilding industry heading to huge oversupply

The LNG shipbuilding industry appears to be doubling down on building new carriers, ignoring the global shift to a low carbon economy and putting itself into an even worse oversupply situation than a year ago, we find in our updated report.

Seasonal forecast of two-metre temperature and precipitation in Tanzania: A hybrid cluster and point-by-point machine learning approach

Seasonal forecasting of atmospheric parameters is important in various fields including agriculture. This study tests how machine learning can complement dynamic models using Tanzanian seasonal forecasts and finds this process uses far less computational power.

Overconfidence in climate overshoot

Even if it is possible to reverse the rise of global temperatures after a temporary overshoot of 1.5°C, some climate damages triggered at peak warming, including rising sea levels, will be irreversible, according to a new study published today in Nature.

Setting 1.5°C compatible wind and solar targets

Based on global energy system modelling sense-checked against key national studies, this report presents new analysis on what a 1.5°C-aligned rollout of wind and solar could look like for key countries. It aims to inform target setting for 2030, 2035 and beyond in third generation NDCs.

Solar geoengineering: a note to inform discussions on physical climate impacts, risks and governance issues

With international efforts on climate action still not on track to limit warming to 1.5°C, technological fixes that aim to intentionally alter the Earth’s climate, such as solar geoengineering, might seem like appealing options for tackling global warming. But they come with questions in terms of feasibility, impacts and risks, governance and geopolitics, and who may or may not benefit.

Technical guide for the development of long-term low emission development strategies in Africa

This technical guide proposes concrete steps and actions to help African countries develop strong, high-performing Long-Term Low Emission and Climate Resilient Development Strategies that chart a low-emission development path, build resilience, encourage innovation, and create new opportunities for green growth.

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Decarbonisation targets and 1.5℃ pathways

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ZERO IN on the remaining carbon budget and decadal warming rates