Considering cryosphere and warming uncertainties together implies drastically increased risk of threshold crossing in the cryosphere, even under lower-emission pathways, and underscores the need to halve emissions by 2030 in line with the 1.5 °C limit of the Paris Agreement.

A key risk of climate change is the potential crossing of abrupt and/ or irreversible thresholds, often called tipping points. The need for improved understanding of such risks, as well as what is required to minimize them, is now also explicitly acknowledged by climate policy. ‘Abrupt’ means a much faster change than usual for that system, while ‘irreversible’ on a given timescale means that the system will not be able to recover to its initial state on a similar timescale. Some changes may be reversible on human timescales, after decades or centuries, whereas others may take millennia. For the cryosphere, which is not only particularly vulnerable to climate change but is also a key driver of sea-level rise, the latest IPCC assessment confirms again that several of its elements are susceptible to such threshold behaviour. Examples of these include the potential melting of the Greenland and Antarctic ice sheets or permafrost thaw.

With the atmosphere already at a current warming of more than 1.1 °C, IPCC assessments indicate that the risk of exceeding thresh- olds is moderate, and could be high with warming above 1.5 °C (using likelihoods as defined in the IPCC reports). Limiting warming in line with the Paris Agreement might still suffice to avoid passing multiple thresholds. The precise nature of Earth system thresholds, however, is subject to considerable uncertainties. While those temperature thresholds are usually accounted for, the range of possible temperature responses to emissions pathways as assessed by the IPCC7 is often less explicitly considered. In the following sections, we discuss both dimensions of uncertainty and implications for risk assessments of cryospheric threshold crossing under different emissions pathways.

Fig 1: Joint uncertainties of cryospheric thresholds and losses, sea-level rise and warming outcomes of emissions pathways.

Publications

Spatially resolved emulated annual temperature projections for overshoot pathways

This study presents a new dataset of annual temperature projections for different overshoot pathways (when the 1.5 °C of global warming limit is exceeded). The data offers a unique opportunity to study local and regional climate change impacts of a range of overshoot scenarios, including when temperature thresholds might be exceeded, and by how much.

Geological Net Zero and the need for disaggregated accounting for carbon sinks

This study in Nature show that definitions of net zero now in widespread use will not actually stop global warming. The paper demonstrates that relying on natural carbon sinks, such as in forests or oceans, to 'offset' ongoing fossil fuel emissions will lead to continued warming.

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.

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.

Fracking the Kimberley: the Canning Basin development plans

We've calculated the climate implications of fracking the Canning basin, part of the remote and pristine Kimberley region in Western Australia. Four companies have their eyes on this region, home to the endangered bilby.

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.

How can event attribution science underpin financial decisions on Loss and Damage?

With climate extremes hitting nations across the globe, disproportionately burdening vulnerable developing countries, funding for loss and damage is an acute need. Attribution science can provide useful information for decision makers.

Australia's global fossil fuel carbon footprint

This report unpacks the global carbon footprint from Australia's exported fossil fuels, especially coal and gas; exports that are set to continue at the same level through to 2035, threatening the 1.5˚C warming limit.
Australia has a global carbon footprint that far exceeds its economic size and population - and is responsible for around 4.5% of global fossil carbon dioxide emissions, with 80% of those emissions coming from its fossil fuel exports.

Achieving net zero greenhouse gas emissions critical to limit climate tipping risks

Current climate policies are putting Earth on a path to a high risk of triggering climatic tipping points – even if temperatures return to below 1.5°C of global warming after a period of overshoot. A new study finds that the risk of crossing these thresholds increases with every additional 0.1 °C of overshoot above 1.5 °C and strongly accelerates above 2.0 °C. These risks can be minimised if stringent emissions reductions are taken in the next decade, and net zero greenhouse gas emissions are met and maintained.

About us

Decarbonisation targets and 1.5℃ pathways

Comment

Only halving emissions by 2030 can minimise risks of crossing cryosphere thresholds