That gap is what motivated a team led by Sarah Safieddine of LATMOS/IPSL in Paris to attempt something no one had done before: a global, day-and-night intercomparison of six skin temperature datasets spanning 2008 to 2022. The study, published in the journal Earth Observation, brings together the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, the European Space Agency’s Land Surface Temperature Climate Change Initiative product (LST CCI v3.00), the ESA CCI and Copernicus Climate Change Service sea surface and sea ice temperature analysis, the ERA5 reanalysis produced by the European Centre for Medium-Range Weather Forecasts, and two distinct products derived from the Infrared Atmospheric Sounding Interferometer (IASI) flying on the Metop satellites: the EUMETSAT all-sky Climate Data Record and a newly developed clear-sky neural-network retrieval. The verdict after fifteen years of data is strikingly coherent: the fingerprint of climate change is unmistakable across nearly all of them, with a handful of fascinating regional exceptions.

The technical challenge of comparing these products is considerable, because each measures something subtly different. Thermal infrared instruments such as MODIS and IASI retrieve skin temperature from radiances in the atmospheric window between 8 and 13 micrometers, where most natural surfaces emit close to a perfect blackbody. By inverting Planck’s law, accounting for surface emissivity, the instruments convert measured radiance into temperature. But infrared retrievals only work under cloud-free skies, and atmospheric water vapour always leaves its mark. Microwave radiometry can peer through clouds, but its surface emissivity is far more variable and its spatial resolution much coarser. Reanalysis products like ERA5 offer complete, all-sky fields, yet their skin temperature is a model variable constrained by data assimilation rather than a direct observation, making it sensitive to how the model parameterises soil, vegetation, and snow. No single dataset can claim to be the universal truth, which is precisely why systematic intercomparison matters.

The team harmonised everything onto a common one-degree grid, restricted the analysis to comparable local solar times between roughly 09:30 and 10:30 in the morning and 21:30 and 22:30 in the evening, and applied dataset-appropriate cloud filtering. Over land, the results were largely reassuring. Daytime global means agreed within about 2 kelvin across the datasets, and the deseasonalised anomalies, which strip away the annual cycle to reveal underlying variability, tracked each other closely. The major modes of interannual variability, including the strong 2015 to 2016 El Niño warming and the subsequent 2020 to 2022 La Niña cooling, appeared consistently in every record, a sign that the fundamental climate signal is robust regardless of which instrument is doing the measuring.

Two systematic quirks did emerge, however, and both carry lessons for anyone using these products. The ESA LST CCI dataset ran consistently warmer than the others, but the team traced this to viewing geometry rather than calibration error: LST CCI restricts retrievals to view zenith angles within 22 degrees of nadir, while MODIS averages across its full 60-degree swath, where longer atmospheric paths and angular emissivity effects systematically depress retrieved temperatures. More concerning were step-like discontinuities in the LST CCI anomalies at sensor transitions, when the record switched from AATSR to MODIS Terra in 2012 and to Sentinel-3B’s SLSTR-B in 2018, indicating residual inhomogeneities that users of this version must treat with caution. At night, MODIS revealed a second surprise: a pervasive cold bias relative to every other product, larger than can be explained by its slightly later overpass time alone. Previous validation studies have found average nighttime biases of around minus 1.6 kelvin against ground stations, with cloud-screening issues and surface heterogeneity in snowy, icy, and arid regions likely contributing.

Over the ocean, the picture was cleaner still. Because the sea surface is far more homogeneous than land, inter-dataset biases between IASI, ERA5, and the ESA CCI/C3S analysis generally stayed below 1 kelvin, with root-mean-square errors near 1 kelvin over the open ocean. The largest discrepancies clustered at high latitudes, where cloud detection, sea-ice contamination, and weak thermal contrast degrade infrared retrievals, and where the very definition of skin temperature diverges across products. One subtle caveat the authors highlight concerns clear-sky sampling itself: during the 2020 to 2022 La Niña, increased tropical cloudiness reduced the availability of clear-sky IASI retrievals, pulling the IASI global mean cooler in a way that reflects sampling changes rather than genuine surface cooling. It is a reminder that even carefully constructed satellite climate records can be modulated by where and when clouds happen to allow a glimpse of the surface.

The heart of the study lies in its trend analysis. Using the robust Theil-Sen estimator on yearly deseasonalised averages, with significance assessed by the Mann-Kendall test, the team mapped warming and cooling across the globe for morning and evening overpasses separately. The dominant signal is unambiguous: skin temperatures have risen since 2008, more strongly over land than over the ocean, and most intensely at high northern latitudes. Alaska and Siberia light up in every dataset, a spatial fingerprint of Arctic amplification, the well-documented phenomenon by which the Arctic warms nearly four times faster than the global average. Daytime land trends ranged from +0.04 to +0.12 kelvin per year depending on the dataset, while nighttime land trends spanned +0.05 to +0.11 kelvin per year, with the all-sky ESA CCI/C3S product showing a modest oceanic warming of about +0.03 kelvin per year consistent with the clear-sky records.

But the most eye-catching findings are the exceptions, places where the planet’s skin is cooling even as the globe warms. India shows significant daytime cooling across all six datasets, a signal the authors link to rising aerosol emissions, which scatter sunlight and offset part of the greenhouse gas warming, compounded by cloud effects that vary seasonally and by time of day, and by land-use change and greening. Parts of central and eastern Africa cool as well, plausibly because increased cloud cover and latent heat release from more intense rainfall suppress surface temperatures. And in the southeastern Pacific off South America, a coherent zone of cooling sits squarely over the Humboldt Current upwelling system, where strengthening alongshore winds drive Ekman divergence and draw cold subsurface water to the surface, a wind-driven mechanism that can produce local cooling even amid global ocean warming, further modulated by Pacific decadal variability on these short timescales.

The study also showcases the growing sophistication of retrieval science. The new IASI neural-network product uses 87 carefully selected window-region channels, discards those sensitive to carbon dioxide to improve long-term stability, and incorporates monthly, time-varying emissivities from the CAMEL database, an important refinement given that neglecting emissivity trends can overestimate global skin temperature trends. The EUMETSAT Climate Data Record, retrained on more than 120 million IASI observations, produces smoother time series that pass significance tests more often, while the neural-network product offers greater independence from ERA5. With the IASI constellation guaranteed through at least 2030 and the IASI-New Generation series extending coverage toward 2045, Earth’s skin temperature is poised to become a cornerstone of climate monitoring, offering a direct, diurnally resolved view of how our planet’s surface responds to a changing atmosphere, one morning and one evening at a time.

Subject of Research: Multi-satellite intercomparison of land, sea, and ice skin temperature trends from 2008 to 2022

Article Title: Assessing Earth's skin temperature trends: consistent signals from IASI, MODIS, ESA CCI and ERA5

Article References: Safieddine, S., Sinnathamby, S., Hadji-Lazaro, J., Doutriaux-Boucher, M., Ghent, D., Whitburn, S., Clarisse, L., & Clerbaux, C. (2026). Assessing Earth's skin temperature trends: consistent signals from IASI, MODIS, ESA CCI and ERA5. Earth Observation, 1(1), 59-75. https://doi.org/10.5194/eo-1-59-2026

Image Credits: AI Generated

DOI: 10.5194/eo-1-59-2026

Keywords: skin temperature, land surface temperature, sea surface temperature, IASI, MODIS, ESA CCI, ERA5, climate change, Arctic amplification, aerosol cooling, upwelling, satellite remote sensing

The research, led by Giulia Mattavelli, Francesco Crottini, and Gerardo Salvato of the University of Pavia and Istituti Clinici Scientifici Maugeri, builds on a decade of intriguing but contested observations linking skin temperature to how we perceive our bodies. Earlier studies of the rubber hand illusion, in which synchronous stroking makes people adopt a fake hand as their own, reported cooling of the real limb, but later replications produced inconsistent results, likely because of differences in paradigms, measurement techniques, and how temperature changes were quantified. More robust effects emerged from the mirror box illusion, the paradigm used in the new study, in which participants tap the index fingers of both hands while viewing the reflection of their right hand in a mirror aligned with the body midline, leaving the left hand hidden from view. When the tapping is synchronous, many people come to feel that the reflected right hand is actually their concealed left hand, and their hands measurably cool.

Thirty-six healthy right-handed adults, aged 18 to 47, took part in the experiment. Each participant performed 100 tapping trials in a synchronous condition, where both index fingers moved toward and away from the mirrors simultaneously, and an asynchronous condition, where the fingers moved in opposite directions at the same tempo. Movement frequency and total movement count were matched, so only the visuomotor congruence differed between conditions. The setup created a deliberate conflict between what participants saw, a right hand reflected on the left side of space, and what they felt proprioceptively, a left hand hidden under a cloak. After each condition, participants rated how strongly the hand in the mirror felt like their left hand and verbally estimated the position of their hidden left index finger, while an infrared thermal camera captured the temperature of both hands before and after each block.

The illusion worked as expected. Synchronous stimulation produced significantly stronger agreement with the statement that the hand in the mirror felt like the participant’s left hand, with mean ownership ratings of 1.72 compared with minus 0.36 in the asynchronous condition. The perceived position of the hidden left index finger also drifted substantially toward the mirror after synchronous tapping, averaging nearly 47 millimeters of displacement versus about 11 millimeters after asynchronous tapping. Crucially, thermal imaging revealed a bilateral reduction in skin temperature following the synchronous condition, with an average decrease of 0.363 degrees Celsius compared with 0.155 degrees after asynchronous stimulation, a difference that was statistically significant for both hands. Within individual participants, larger temperature drops covaried with larger proprioceptive drift, directly tying the physiological change to the spatial recalibration of the body image.

The central novelty of the study lay in what happened in the brain during these manipulations. Using 64-channel EEG recordings and independent component analysis, the researchers identified a right-lateralized cluster of sources centered on premotor and supplementary motor areas and parietal cortex whose oscillatory activity differed between conditions in the theta to low-alpha range, roughly 4 to 9 hertz. Asynchronous tapping, which confronts the brain with a visuo-motor mismatch, produced stronger event-related desynchronization in this band around 300 milliseconds after movement onset, suggesting heightened engagement of sensorimotor circuits to process the sensory incongruence. Synchronous tapping, by contrast, was associated with greater inter-trial phase coherence around 400 milliseconds, indicating more consistent timing of neural responses when the multisensory signal was coherent and integrated.

When the researchers correlated the power in this 4-to-9-hertz band with the temperature changes measured by thermal imaging, a striking pattern emerged: within the same participant, increases in theta/low-alpha power during the illusion covaried with larger reductions in skin temperature, a significant repeated-measures correlation. Notably, the oscillatory power did not correlate with the subjective vividness of the illusion or with proprioceptive drift. This dissociation, the authors argue, fits the view that body ownership is not a single unified representation but an emergent construct supported by distributed neural systems that handle partially distinct aspects of bodily self-representation, with thermoregulatory signals coupled to the sensorimotor layer rather than to conscious ratings alone.

To probe whether these local oscillations were embedded in larger-scale communication, the team reconstructed activity at the cortical source level and computed functional connectivity using the debiased weighted phase lag index, a metric that quantifies phase synchronization while minimizing artifacts from volume conduction. Clustering the significant connections revealed six distinct connectivity patterns induced by the illusion. One of them, a distributed frontoparietal-insular network linking bilateral sensorimotor cortices, superior parietal regions, the right supramarginal gyrus, and the left anterior insula and operculum, was directly associated with temperature: stronger connectivity within this module in the theta/low-alpha band predicted greater subsequent drops in hand temperature. The insula’s involvement is particularly telling, since it is a well-established hub for thermosensory processing, receiving spinothalamic input about cutaneous temperature and integrating it with interoceptive and emotional states.

The network identified in healthy brains bears a remarkable resemblance to the circuitry disrupted in clinical conditions. In an earlier study by the same group, stroke patients with disturbed sensation of limb ownership showed reduced limb temperature alongside lesions involving the right insula and disconnection between bilateral parietal hubs, including the primary and secondary somatosensory cortices and the inferior parietal gyrus. Abnormal temperature patterns have also been documented in complex regional pain syndrome, body integrity dysphoria, and anorexia nervosa, all conditions in which bodily self-awareness is disturbed. The convergence between network-level dynamics in healthy participants and patterns of disconnection in patients suggests, the authors contend, that thermosensory signals constitute a fundamental component of the neural architecture supporting bodily self-awareness rather than an epiphenomenal consequence of ownership changes.

The findings also resonate with classic animal work. Lesion studies in non-human primates reported that damage to premotor and posterior parietal cortices produced persistent cooling of the contralateral limb even without direct autonomic injury, hinting that cortical regions classically associated with sensorimotor integration also help regulate peripheral vasomotor responses. The new human data extend this idea by showing that activity in frontoparietal regions covaries with temperature changes during an ownership manipulation in real time. From a predictive-processing perspective, ownership illusions may engage sensory reweighting in which visual information is prioritized over competing somatosensory signals, and thermosensory input, like touch, may be downweighted during multisensory conflict, with the present oscillatory and connectivity patterns providing complementary windows onto that process.

The study has limitations the authors acknowledge: the sample comprised only healthy young adults, EEG source localization cannot definitively pinpoint anatomical generators, temperature was sampled before and after each condition rather than continuously, and the correlational design precludes causal claims about whether thermosensory signals drive ownership updates. Even so, the practical implications are tantalizing. Warming a limb has been shown to strengthen body ownership in healthy people and to correlate with recovery of ownership disturbances in a patient with somatoparaphrenia, and thermal feedback is now being built into advanced prosthetic limbs that restore natural temperature sensation to amputees. Understanding the rhythmic dialogue between frontoparietal circuits, the insula, and the skin could therefore open new rehabilitation strategies for disorders of bodily self-awareness, from stroke to eating disorders, and may even guide the design of prostheses that feel genuinely like part of the body. For now, the message is vividly simple: the warmth of your hands and the feeling that they are yours are entangled in the same slow brainwaves.

Subject of Research: The neural oscillatory mechanisms by which thermosensory signals are integrated into body ownership

Article Title: Oscillatory dynamics within fronto-insular-parietal networks integrate thermosensory signals into body ownership

Article References: Mattavelli, G., Crottini, F., Gorrino, I., Arrigoni, E., Maiocchi, C., Pisoni, A., Bottini, G., & Salvato, G. (2026). Oscillatory dynamics within fronto-insular-parietal networks integrate thermosensory signals into body ownership. iScience, 29(10), Article 117679. https://doi.org/10.1016/j.isci.2026.117679

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117679

Keywords: body ownership, thermosensory signals, skin temperature, EEG, theta oscillations, mirror box illusion, insula, frontoparietal network, functional connectivity, bodily self-awareness, thermal imaging, neuroscience