The terrestrial CO₂ exchange in Arctic ecosystems plays an important role in the global carbon cycle and is particularly sensitive to the ongoing warming experienced in recent years. To improve our understanding of the atmosphere–biosphere interplay, we evaluated the state of the terrestrial pan-Arctic carbon cycling using a promising data assimilation system in the first 15 years of the 21st century. This is crucial when it comes to making predictions about the future state of the carbon cycle.

We demonstrate here that nonlinear character of ice sheet dynamics, which was derived naturally from the conservation laws, is an effective means for propagating high-frequency forcing upscale.

Net heat flux dominates the frontogenesis of the NPSTF from October to December, while oceanic meridional temperature advection contributes equally as much or even more net heat flux in January and February. The atmosphere is critical to frontogenesis through net heat flux and the Aleutian low, the latter of which benefits meridional temperature advection.

The effect of human activities on the probability of winter wind storms like the ones that occurred in Western Europe in January 2018 is analysed using multiple model ensembles. Despite a significant probability decline in observations, we find no significant change in probabilities due to human influence on climate so far. However, such extreme events are likely to be slightly more frequent in the future. The observed decrease in storminess is likely to be due to increasing roughness.

Our study highlights the importance of tides in controlling the spatial and temporal distributions North Sea primary production based on numerical experiments. We identified two different response chains acting in different regions of the North Sea. (i) In the southern shallow areas, strong tidal mixing dilutes phytoplankton concentrations and increases turbidity, thus decreasing NPP. (ii) In the frontal regions, tidal mixing infuses nutrients into the surface mixed layer, thus increasing NPP.

By analysing old wind direction observations taken aboard sailing ships, it has been possible to build an index quantifying the moisture transport from the equatorial Pacific into large areas of Central America and northern South America starting in the late 19th century. This transport is deeply related to a low-level jet known as the Choco jet. Our results suggest that the seasonal distribution of the precipitation associated with this transport could have changed over the time.

Processes causing the same global-average radiative forcing might lead to different global temperature changes. We expand the theoretical framework by which we calculate paleoclimate sensitivity with an efficacy factor. Applying the revised approach to radiative forcing caused by CO₂ and land ice albedo perturbations, inferred from data of the past 800 000 years, gives a new paleo-based estimate of climate sensitivity.

Quantifying hydroclimate variability beyond the instrumental period is essential for putting fluctuations into long-term perspective and providing a validation for climate models. We evaluate, in a virtual setup, the potential for generating millennium-long summer precipitation reconstructions over south-eastern Asia. We find that performing a real-world reconstruction with the current available proxy network is indeed feasible, as virtual-world reconstructions are skilful in most areas.