Earth has grown a full shade darker since 2001. In practical terms, the planet is reflecting less sunlight back into space than it used to, resulting in a change in climate.
After analyzing satellite data, a team led by Norman Loeb at NASA’s Langley Research Center in Hampton, Virginia, uncovered this previously unknown inequality between Earth’s northern and southern hemispheres.
The trend, measured between 2001-2024, matters not only because it nudges the global energy balance, but also because it isn’t uniform.
The Northern Hemisphere is dimming faster than the Southern – an imbalance that adds extra heat where ice and snow are already in retreat.
Small shift, big consequences
At the top of the atmosphere, Earth handles about 240–243 watts of solar energy per square meter.
Against that huge background, the researchers found a hemispheric divergence of roughly 0.34 watts per square meter each decade.
It sounds tiny, but climate change is a story of small, persistent numbers. An extra trickle of energy, applied year after year, can alter sea-ice seasons, snow cover, cloud fields, winds, and currents in ways that reinforce the original shove.
Historically, the two halves of the planet haven’t balance perfectly. The south tends to gain a touch more solar energy aloft; the north tends to lose a touch more.
Normally, the atmosphere and oceans ferry heat back and forth across the equator and smooth the difference.
However, over the last two decades, that conveyor hasn’t fully kept pace. The north’s darkening has outstripped the system’s ability to compensate.
Ice, snow, and surface color
One driver is straightforward: reflectivity, or albedo. Bright surfaces – sea ice, snow, and some cloud tops – bounce sunlight back into space. Replace them with darker ocean or bare ground and more energy sticks around.
The Northern Hemisphere has seen pronounced declines in spring snow cover and summer Arctic sea ice.
Swapping white for dark doesn’t just absorb more light; it makes it harder for ice and snow to rebound the next season, a classic positive feedback.
Cleaner air, darker Earth
The atmosphere is the second driver. Water vapor and clouds influence how much sunlight gets reflected or trapped. But the clearest fingerprint comes from aerosols – the tiny particles that scatter light and seed cloud droplets.
In the north, aerosol pollution has dropped sharply thanks to tighter air-quality rules in North America, Europe, and parts of East Asia.
That’s a public health victory. It also means fewer particles to brighten clouds or scatter sunlight, leaving the hemisphere a bit less reflective.
By contrast, the south has had sporadic aerosol boosts from natural events.
Australia’s extreme bushfire seasons lofted smoke high into the atmosphere, and the Hunga Tonga-Hunga Ha‘apai eruption injected material that affected upper air reflectivity.
Those intense pulses temporarily restored a bit of “shine” in the south, widening the north–south gap.
Clouds can’t explain a darker Earth
It’s tempting to assume clouds will simply shuffle around and restore symmetry – more low clouds here, fewer there. The new work suggests that safety net has limits.
As sea ice retreats and aerosol levels shift, clouds do respond, but not perfectly and not always in ways that cancel the imbalance.
This finding matters for climate models, which need to capture how aerosols influence droplet formation, how cloud fields evolve over warmer, less icy oceans, and how those changes alter the planet’s overall reflectivity.
Zonal mean anomalies in (A) aerosol–radiation interaction IRF and (B)–SW cloud radiative response for 2001 to 2024. Credit: PNAS
Subtle dark trends reshape climate
Climate warming is powered by a few sustained watts per square meter across Earth.
Layer a steady hemispheric tilt on top – less reflection in the north – and you influence where heat accumulates and how fast ice sheets, mountain glaciers, and permafrost respond.
No single year flips the system, but over decades, a quiet, persistent energy imbalance can reshape seasonal patterns, storm tracks, and regional extremes.
That’s why there’s no case for “brightening” the sky with pollution. Aerosols are short-lived – days to weeks – while carbon dioxide lingers for centuries.
Trying to prop up planetary reflectivity by tolerating dirtier air would cost lives and do nothing about ocean acidification or long-term greenhouse warming.
The practical path is already under way: keep cutting CO₂ and methane, keep cleaning the air, and keep sharpening our understanding of short-lived particles and clouds so forecasts of their effects continue to improve.
Watching Earth’s glow fade
The Arctic remains the bellwether. Sea-ice extent and thickness, the timing of spring snowmelt, and the evolving brightness of northern land and ocean surfaces will continue to shape the north’s albedo.
In the south, the occasional volcanic eruption or severe fire season will deliver temporary aerosol bursts.
Meanwhile, the oceans’ ability to ferry heat across the equator will be crucial; if the hemispheric split persists, models will need to lean harder into regional details, not just global averages.
The bottom line is simple: Earth is getting darker, especially in the north. That means a little more solar energy is sticking around each year.
It’s a quiet signal, not a blaring siren, but in climate terms, a quiet signal that never lets up can be just as powerful.
Rising global emissions of hydrogen over the past three decades have added to the planet's warming temperatures and amplified the impact of methane, one of the most potent greenhouse gases, according to new research published in Nature.
Authored by an international consortium of scientists known as the Global Carbon Project, the study provides the first comprehensive accounting of hydrogen sources and sinks.
"Hydrogen is the world's smallest molecule, and it readily escapes from pipelines, production facilities, and storage sites," said Stanford University scientist Rob Jackson, senior author of the Nature paper and chair of the consortium.
"The best way to reduce warming from hydrogen is to avoid leaks and reduce emissions of methane, which breaks down into hydrogen in the atmosphere."
Amplifying methane
Unlike greenhouse gases including carbon dioxide and methane, hydrogen itself does not trap heat in Earth's atmosphere. Through interactions with other gases, however, hydrogen indirectly heats the atmosphere roughly 11 times faster than carbon dioxide during the first 100 years after release, and around 37 times faster during the first 20 years.
The main way hydrogen contributes to global warming is by consuming natural detergents in the atmosphere that destroy methane.
"More hydrogen means fewer detergents in the atmosphere, causing methane to persist longer and, therefore, warm the climate longer," said lead study author Zutao Ouyang, an assistant professor of ecosystem modeling at Auburn University, who began the work as a postdoctoral scholar in Jackson's lab in the Stanford Doerr School of Sustainability.
In addition to extending the heat-trapping life of methane, hydrogen's reactions with nature's detergents also produce greenhouse gases such as ozone and stratospheric water vapor, and affect cloud formation.
The researchers estimate hydrogen concentrations in the atmosphere increased by about 70% from preindustrial times through 2003, then briefly stabilized before picking up again around 2010. Between 1990 and 2020, hydrogen emissions increased mostly because of human activities, the authors found.
Vicious cycle
Major sources include the breakdown of chemical compounds, including methane, which itself has been rapidly building up in the atmosphere because of growing emissions from fossil fuels, agriculture, and landfills.
It's a vicious cycle: Because methane breaks down into hydrogen in the atmosphere, more methane means more hydrogen. More hydrogen, in turn, means methane emissions stick around longer, doing more damage.
"The biggest driver of hydrogen increase in the atmosphere is the oxidation of increasing atmospheric methane," said Jackson, the Michelle and Kevin Douglas Provostial Professor at Stanford. Since 1990, the authors estimate the annual emissions from this source of hydrogen has grown by about 4 million tons, to 27 million tons per year in 2020.
Other important hydrogen sources since 1990 include leakage from industrial hydrogen production and the process of nitrogen fixation, which farmers harness to grow legume crops like soybeans. Natural sources of hydrogen, such as wildfires, varied from year to year without a consistent trend across the 1990-2020 period.
Future energy systems
The most detailed data in the study covers the decade ending in 2020, drawing on multiple datasets and models and incorporating emission factors for hydrogen and precursor gases such as methane and other volatile organic compounds.
The authors found 70% of all hydrogen emissions were removed during this period by soil, largely through bacteria consuming hydrogen for energy.
Overall, the buildup of hydrogen in our atmosphere has contributed a fraction of a degree (0.02 degrees Celsius) to the nearly 1.5 degree Celsius increase in average global temperatures since the Industrial Revolution.
According to Ouyang, Jackson, and colleagues, this temperature increase from rising hydrogen concentrations is comparable to the warming effect of the cumulative emissions from an industrialized nation such as France.
Any contribution to warming could diminish the climate benefits of replacing fossil fuels with hydrogen, which has long garnered interest from some politicians, executives, and academics as a clean-burning alternative to oil and gas for heavy industry and transportation.
More than 90% of hydrogen production today is enormously energy intensive. It's derived mainly from coal gasification or steam methane reforming, which have large carbon footprints.
But because it's possible in theory to produce hydrogen with renewable energy and close to zero carbon emissions, most scenarios for decarbonizing the world's energy systems in the coming decades assume low-carbon hydrogen production will dramatically increase.
"We need a deeper understanding of the global hydrogen cycle and its links to global warming to support a climate-safe and sustainable hydrogen economy," Jackson said.
Ouyang worked on the research as a postdoctoral scholar in the Jackson Lab in the Stanford Doerr School of Sustainability's Department of Earth Science. He is now an assistant professor at Auburn University.
Jackson is a professor of Earth system science in the Doerr School of Sustainability and a senior fellow in the school's two institutes, the Woods Institute for the Environment and Precourt Institute for Energy.
Stanford co-authors not mentioned above include Steve Davis, a professor of Earth system science in the Doerr School of Sustainability and senior fellow at the Precourt Institute for Energy.
