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

Mapping the climate risk to urban forests at city scale

This study uses an urban tree inventory and high-resolution climate projections to identify species and locations at risk from climate change in Melbourne. It finds that half of the tree species in Melbourne are at risk from heat stress, which could climb to two thirds in 2050.

The 1.5°C limit and risks of overshoot

This briefing looks at what the 1.5°C limit means in terms of adaptation and loss and damage for the most vulnerable countries and regions. It finds that slowing down warming is critical to buy us time to adapt and also to avoid irreversible loss and damage. Even if warming rises above 1.5°C (overshoot) we can bring it down again with ambitious emissions reductions.

Hydrologic interpretation of machine learning models for 10-daily streamflow simulation in climate sensitive upper Indus catchments

This study augments physical hydrological modeling with machine learning models to simulate surface water flows in Upper Indus water catchments in Pakistan.

Le seuil de +1,5°C et le risque de dépassement de ce seuil

Ce rapport examine ce que la limite de 1,5 °C signifie en termes d'adaptation et de pertes et dommages pour les pays et régions les plus vulnérables. Il constate qu'il est essentiel de ralentir le réchauffement pour nous donner le temps de nous adapter et pour éviter des pertes et des dommages irréversibles. Même si le réchauffement dépasse 1,5 °C, nous pouvons le faire baisser à nouveau en réduisant les émissions de manière ambitieuse.

Representing natural climate variability in an event attribution context: Indo-Pakistani heatwave of 2022

New study finds that the 2022 Indo-Pakistani heatwave was both more likely to occur and more intense due to increasing global warming – even when accounting for the effects of natural climate variability and the forced response to anthropogenic climate change.

Extreme terrestrial heat in 2023

Multiple relentless heatwaves occurred in 2023, with much of the world experiencing at least 20 more heatwave days than the 1991–2020 average. This study looks at prominent and record-breaking events around the world.

Climate impacts in northern forests

Northern forests hold around 54% of the world’s total terrestrial carbon stock and contribute more than one-third to our global terrestrial carbon sink. This report reviews the impact of human induced climate change on northern temperate and boreal forests.

Effects of idealised land cover and land management changes on the atmospheric water cycle

This study investigates how land cover and land management affects atmospheric moisture transport using global climate models. It finds that cropland expansion is generally causing a drying and reduced local moisture recycling, while afforestation and irrigation expansion generally cause wetting and increased local moisture recycling.

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A better integration of health and economic impact assessments of climate change

This study lays out how to integrate the economic repercussions of climate change on people's health with direct health impacts. The authors argue this could provide more realistic scenario projections than health studies on their own and be more useful for adaptation policy.

Kipppunkte und kaskadische Kippdynamiken im Klimasystem

Dieser im Auftrag des deutschen Umweltbundesamtes erstellte Bericht befasst sich mit Kippelementen - sensible Komponenten des Erdsystems, die bei Überschreiten kritischer Schwellenwerte (Kipppunkte) irreversiblen Veränderungen ausgesetzt werden können. Er unterstreicht, dass selbstverstärkende Mechanismen zwischen diesen Elementen zu schnellen, irreversiblen Veränderungen führen können.

Hitzestress und Anpassungsmaßnahmen in der Metropolregion Berlin-Brandenburg

Städte sind dabei besonders anfällig für Hitzestress. Deshalb betrachten wir in diesem Bericht die Folgen des Klimawandels auf die Metropolregion Berlin-Brandenburg, mit einem speziellen Fokus auf die Auswirkungen von Hitzestress und die Entwicklung von Anpassungsstrategien.

Limited reversal of regional climate signals in overshoot scenarios

This peer-reviewed paper analyses what happens in an 'overshoot scenario' - where temperature rise peaks just above 1.5°C, but then return below it by the end of the century. It concludes that despite a drop in warming, regional climate changes may only be partially reversed in the decades after peak warming, demonstrating the value of limiting peak temperatures to as low as possible.

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Decarbonisation targets and 1.5℃ pathways

Comment

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