Multiple relentless heatwaves occurred in 2023, with much of the world experiencing at least 20 more heatwave days than the 1991–2020 average. Prominent and record-breaking events included exceptional wintertime and spring heat in South America, large heatwaves over Europe, Africa and Asia, and a prolonged event over south-eastern USA and Central America.

Key points

Persistent heatwaves across much of the globe were synonymous with the hottest year on record.
Many 2023 heatwaves exhibited record-smashing extreme temperatures, including a widespread heatwave spanning Thailand to Northern China that featured the worst April heatwave in South China on record.
South America saw many prominent heat events, with exceptional heat in winter and early spring that broke all-time summertime records.

2023 was the hottest year on record. The global average temperature was 1.45 °C above pre-industrial (1850–1900) values, beating the previous record, which was set in 2016, by 0.16 °C. Behind this remarkable anomaly were many global temperature records, including: the hottest month and season ever recorded (July and June–August; both approaching 17 °C, which is 0.72 °C and 0.66 °C above average, respectively); daily instances of global temperatures 2 °C above pre-industrial levels; and 23% of land regions setting new extreme heat records. However, these figures hide the plethora of extraordinary daily and regional-scale terrestrial heat extremes, each linked to a combination of large- and local-scale drivers and feedbacks, such as anthropogenic climate change, persistent atmospheric blocking, droughts, adjacent marine heatwaves and the developing El Niño.

Here, we summarize extreme terrestrial heat events during 2023 using ERA5 reanalysis. Not all events — of which there are many — are discussed, and Australia is omitted, since record-breaking heat extremes over this continent were minimal. Throughout, anomalies are calculated with respect to 1991–2020.

Heatwave activity in 2023

Climate impacts and risks

Publications

Humid heat exceeds human tolerance limits and causes mass mortality

With critical physiological limits to human heat tolerance drawing ever closer, this Comment highlights the urgent need to limit further climate warming and emphasises the adaptation challenge ahead.

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.

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.

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.

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.

Evaluating the near and long-term role of carbon dioxide removal in meeting global climate objectives

For 1.5°C pathways with limited overshoot, most of the mitigation between now and 2030 should come from emissions reductions (70%), with reductions from cutting non-CO2 emissions (20%) and land-based carbon dioxide removals such as afforestation and preventing deforestation (10%) making up the remainder.

Increasing April-May rainfall, El Niño and high vulnerability behind deadly flooding in Afghanistan, Pakistan and Iran

This April and May, large regions of central Asia were hit by a series of storms resulting in heavy downpours and flash flooding. Researchers assessed what extent human-induced climate change altered the likelihood and intensity of the weather conditions that caused the floods.

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Extreme terrestrial heat in 2023