Top-of-atmosphere radiation over the last millennium reconstructed from proxies

Intensification of the tropospheric warming and weakening of the lower stratospheric cooling: Insights from long-term (1980–2024) multi data sets

Reconstruction and attribution of Late-Pleistocene changes in the Earth’s energy imbalance

The Earth’s energy imbalance (EEI) that develops at the top of the atmosphere is accommodated by gains or losses of energy in Earth’s heat reservoirs, leading to temperature and sea level change. The global ocean has stored about 90% of the EEI from anthropogenic forcing, but the attribution of past changes of EEI remains largely unknown, thus obscuring our understanding of past climate change. Here, we reconstruct changes in mean ocean temperature over the past 150,000 years that, with a reconstruction of ice sheet–volume changes, allow us to isolate the contributions of the dominant ocean and ice sheet heat reservoirs to the global energy inventory as well as to derive their associated contributions to EEI. We attribute orbital-scale EEI variability to joint precessional and CO2 forcing that caused changes in rates of ice sheet energy storage. In contrast, millennial-scale EEI variability can be attributed to radiative responses to decreases in the Atlantic meridional overturning circulation and increasing CO2 during Heinrich stadials that caused changes in rates of ocean energy storage.

Major role for internal variability in tropical Pacific warming pattern over satellite era.

Home to El Niño, the tropical Pacific is a key player in the global climate system. While most of the planet has warmed during the satellite era of 1982-2024, the eastern tropical Pacific surface has mysteriously cooled. What is troubling is that fully coupled global climate models mostly fail to simulate this distinctive pattern. By replacing wind stress applied to the ocean with observations, here we show that climate models successfully reproduce the La Niña-like (LN) trend pattern over the satellite era as well as the opposite decadal transition observed during the 1970s. Detailed analysis reveals that the LN (El Niño-like) surface temperature pattern is associated with a multidecadal intensification (slowdown) of the trade winds and deepened (shoaled) thermocline in the western equatorial Pacific. Averaging out cyclic internal variability, longer-term trends from the 1950s are in broad agreement with the radiatively forced response in the same models, with much reduced wind and ocean temperature anomalies in the equatorial Pacific compared to those during the satellite era. These results indicate that unforced internal variability largely explains the satellite-era tropical Pacific change. As such, the LN pattern is expected to wane as tropical Pacific decadal variability transitions from its current negative phase, causing worldwide shifts in rainfall, tropical cyclones, and ocean-atmospheric circulations.

Improving simulation of Earth system variability through weakly coupled ocean data assimilation in E3SM

Abstract. Accurate initialization of ocean states is essential for skillful prediction of Earth system variability across seasonal-to-decadal timescales. In this study, we evaluate the impact of a newly developed four-dimensional ensemble variational (4DEnVar)-based weakly coupled ocean data assimilation (WCODA) system within the DOE Energy Exascale Earth System Model version 2 (E3SMv2) on global and regional climate variability. By assimilating monthly ocean temperature and salinity from the EN4.2.1 reanalysis into the fully coupled model, we demonstrate substantial improvements in simulating both interannual and decadal climate variability. Compared with the free-running coupled simulation, the assimilation experiment exhibits markedly enhanced interannual correlations with observations for global mean surface air temperature and precipitation anomalies. The temporal variability of key climate modes, including ENSO, the Indian Ocean Dipole, and multidecadal variability in the Pacific and Atlantic Oceans, also shows markedly improved phase agreement with observations. Regional evaluation over the contiguous United States further shows enhanced skill in simulating winter surface air temperature and precipitation, particularly in the northern and southern regions, respectively, with these improvements linked to improved ENSO simulation. Additional hindcast experiments initialized from the WCODA system exhibit no appreciable initialization shock in the early years and reproduce physically coherent ENSO teleconnection patterns, suggesting the dynamical consistency of the coupled initialization framework. These findings underscore the critical role of coupled forecasts in the data assimilation cycle for propagating observational information across Earth system components. By assimilating ocean reanalysis within the fully coupled framework, the WCODA system enables cross-component information exchange among the ocean, atmosphere, and land, thereby generating dynamically consistent initial conditions that support more accurate simulations of Earth system variability and lay the foundation for seasonal-to-decadal prediction applications.

Marine Heatwaves and NAO-Related Ocean–Atmosphere Variability in the North Atlantic

Increasing greenhouse gas concentrations are placing severe pressure on the Earth system, particularly on the ocean, which plays a vital role in carbon and heat uptake, and overall climate regulation. Consequently, the ocean is experiencing an accelerated warming, leading to an increase in the occurrence of extreme seawater temperature events, called Marine Heatwaves (MHWs). According to the most common definition, an MHW event is identified when local temperatures exceed the 90th percentile threshold of the climatology for at least five consecutive days. In this study, the definition was modified by calculating both the mean and the 90th percentile of SST over the entire available historical period (1982–2022), rather than using a fixed 30-year baseline. While MHWs can develop as a function of multiple drivers (including subsurface heat re-emergence, anomalously warm water masses, ocean heat advection, reduced vertical mixing, and mixed-layer stratification associated with surface heat gain), this study focuses on synoptic-scale atmospheric conditions associated with MHW occurrence and characteristics in the North Atlantic basin, from 1982 to 2022, with the objectives of identifying spatial-temporal trends of MHWs, examining the atmospheric conditions associated with their occurrence and exploring their relationship with prevalent climate variability modes. The results show positive trends in MHW frequency, duration, and intensity, albeit characterised by significant zonal and meridional variability, with noticeable differences between composite patterns of frequency and maximum intensity, according to the prevailing North Atlantic Oscillation (NAO) mode. The annual NAO appears to modulate the spatial distribution of MHWs, with its positive phase favouring MHWs in mid-latitude regions, while the negative phase impacts subpolar and tropical regions. Furthermore, concerning case-specific events, the stationarity of high-pressure systems, with weak pressure gradients, reduced wind speeds and increased solar radiation appears to be associated with the occurrence of the analysed events, while atmospheric instability appears to signal their decline, likely linked to enhanced wind-induced ocean mixing.

Historical Climate and Future Projection in the North Atlantic and Arctic: Insights from EC-Earth3 High-Resolution Simulations

Abstract. This study presents a new set of high-resolution global climate simulations conducted with the EC-Earth3 model, including a 350 year pre-industrial, followed by historical (1850–2014) and future (2015–2100, SSP2-4.5) simulations. The model features a horizontal resolution of ∼ 40 km in the atmosphere and 0.25° in the ocean. The high-resolution EC-Earth3 (EC-Earth3-HR) is compared to the standard-resolution version used in CMIP6 to assess the impact of increased resolution on the representation of key climate variables, focusing particularly on the Arctic and North Atlantic regions. The high-resolution model aligns more closely with reanalysis data, particularly for global mean surface temperature and sea surface temperature. Both model resolutions exhibit similar biases in North Atlantic sea surface temperature and salinity, and in Arctic sea ice concentration, although the higher-resolution version shows regional improvements. The EC-Earth3-HR model captures the observed AMOC variability in the early 2000s, along with the trend and rapid loss event in Arctic sea ice. For future projection under SSP2-4.5, the high-resolution model projects a nearly ice-free Arctic by 2040 – earlier than the standard-resolution model – while simulating less Arctic warming and a more pronounced weakening of the AMOC. We also introduce a framework to diagnose deep-water formation (DWF) in the Labrador, Irminger, and Greenland Seas and to quantify their regional contributions to the AMOC. Applying this framework, we find that projected DWF weakens across all regions, with the largest reduction in the Labrador Sea, making it the dominant contributor to long-term AMOC weakening. By 2100, diagnosed DWF ceases in the Labrador Sea, compared with declines of 62 % in the Greenland Sea and 13 % in the Irminger Sea.