Climate chronicles

In 2023, global full-depth ocean heat content (OHC) reached a record increase of 464 ± 55 ZJ since 1960, with strong heat gain observed in the Southern and Atlantic Oceans. OHC was 16 ± 10 ZJ higher than in 2022, continuing the long-term increasing trend that started in 1960.

Antarctic sea ice extent was the lowest on record in 2023, with an annual mean of 9.81 million km², beating the previous minimum of 2022. Arctic sea ice extent was also low, with an annual mean of 10.49 million km², but did not break any records.

Wildfires burned 384 Mha of land in 2023, the highest since 2017 but 5% lower than the 2001–2022 average. These fires emitted an estimated 2,524 Tg C, 30% of which came from Canada’s record fire season.

Global greening continued into 2023, reaching near-record values that were dominated by regional enhancement in the mid-western USA, Europe, northern Australia and parts of equatorial Africa. In contrast, climatic events contributed to browning signals in Russia, Canada, Mexico and tropical drylands.

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.

Global terrestrial water storage (TWS) anomalies reached a record low of –9.94 cm in 2023, decreasing 0.80 cm from 2022. These reductions largely reflect ongoing TWS losses from glacial melt and groundwater use for irrigation, offset by gains in central and eastern Antarctica and La Niña-related tropical wetting.

2023 saw a multitude of extreme precipitation events across the globe, causing flash flooding, countless fatalities and huge economic losses. Fuelled by a combination of a strong El Niño, record ocean warmth and anthropogenic warming, these events highlight the ongoing risks posed by extreme precipitation in a warming climate.

Global CO₂ emissions for 2023 increased by only 0.1% relative to 2022 (following increases of 5.4% and 1.9% in 2021 and 2022, respectively), reaching 35.8 Gt CO₂. These 2023 emissions consumed 10–66.7% of the remaining carbon budget to limit warming to 1.5°C, suggesting permissible emissions could be depleted within 0.5–6 years (67% likelihood).

In 2023, national and international climate policy advanced in many areas but also faced substantial domestic hurdles in others. Countries agreed on new global initiatives and many major emitters expanded national climate policies. However, others rolled back existing policies and continued to support fossil fuels, slowing down global progress.

Greenhouse gas forcing has increased ocean heat content, with large impacts on the Earth system. This Review outlines observed and projected global and regional changes, revealing an observed 0–2,000 m global increase of 351.4 ± 59.8 ZJ from 1958 to 2019, and a projected increase of 1,874 [1,637–2,109] ZJ by 2100 under SSP5-8.5.

With continued anthropogenic warming, an ice-free Arctic (sea ice area <1 million km²) is inevitable. This Review outlines the various characteristics of an ice-free Arctic, highlighting that future emission trajectories will determine where, how frequently and how long the Arctic will be ice free each year.

Vegetation fires are integral to some ecosystems but can be economically and environmentally destructive. This Review discusses contemporary and future fire regimes, adaptation to fire in the Anthropocene and the need for increased transdisciplinary research to achieve better fire management.

Vegetation on Earth is increasing, potentially leading to a larger terrestrial carbon sink. In this Review, we discuss the occurrence of this global greening phenomenon, its drivers and how it might impact carbon cycling and land-atmosphere heat and water fluxes.

Heatwaves are occurring with increasing frequency and intensity, necessitating prediction so as to minimize loss of life and other impacts. This Review outlines heatwave predictive capabilities at daily to decadal timescales, and discusses heatwave projections with anthropogenic warming.

Water resources are threatened by human activities and climate variability. This Review discusses trends in water storage and availability and examines ways to enhance water-resource resilience through green and grey solutions.

Short-duration rainfall extremes are determined by complex processes that are affected by the warming climate. This Review assesses the evidence for the intensification of short-duration rainfall extremes, the associated drivers and the implications for flood risks.