A warming world

Every day, people measure how warm the air and the sea are. They do it all over the world.

When scientists put all the numbers together, they see something. Earth is a little warmer than it was long ago. The last few years have been the warmest ever measured.

Every day, weather stations, satellites and other instruments measure the temperature of Earth's air and ocean. When scientists put these measurements together, they can work out the average temperature of the whole planet, year by year.

The World Meteorological Organization (WMO) reported in March 2026 that 2025 was about 1.43 °C warmer than the average for 1850 to 1900, a period scientists use as the starting point, before modern industry grew. The warmest year measured so far was 2024, at about 1.55 °C. And the 11 years from 2015 to 2025 were the 11 warmest on record. That may not sound like much, but it is an average over the whole planet, all year long.

The WMO's State of the Global Climate 2025, released on 23 March 2026, combines several international temperature datasets. It finds that 2025 was the second or third warmest year (depending on the dataset) in the 176-year record, at about 1.43 ± 0.13 °C above the 1850–1900 pre-industrial average. 2024, which began with a strong El Niño, remains the warmest at about 1.55 °C; 2025 was slightly cooler partly because of a shift to La Niña conditions, which temporarily cool the planet. The eleven years 2015–2025 are the eleven warmest on record.

Natural variations such as El Niño and La Niña push individual years up or down, which is why scientists judge climate by long-term trends rather than single years. Earth's climate has always changed: NASA notes eight cycles of ice ages and warmer periods in the last 800,000 years, mostly caused by small variations in Earth's orbit. What is different now, NASA says, is that the current warming is happening at a rate not seen in the past 10,000 years.

Air has some gases that hold in heat. They are called greenhouse gases.

They work a bit like a blanket around Earth. Burning coal, oil and gas adds more of these gases. A thicker blanket keeps in more heat.

Some gases in the air, such as carbon dioxide and methane, trap heat. They are called greenhouse gases. Scientists showed that carbon dioxide traps heat back in the mid-1800s. They work a bit like a blanket. When people burn coal, oil and gas for energy, they add more carbon dioxide, and the blanket gets thicker.

Scientists have measured carbon dioxide on Mauna Loa, a mountain in Hawaii, since 1958, and NOAA keeps the record. In 1959, the yearly average was about 316 parts per million. In 2025, it was about 427 parts per million. The IPCC, which reviews the world's climate research, says greenhouse gases from human activities have caused the warming.

Greenhouse gases, chiefly carbon dioxide, methane and nitrous oxide, absorb and re-emit infrared radiation, trapping energy in the Earth system; NASA notes that their heat-trapping nature was demonstrated in the mid-19th century. The Mauna Loa record, begun by Charles David Keeling of the Scripps Institution of Oceanography in 1958 and run in parallel by NOAA since 1974, shows annual mean CO₂ rising from 315.98 parts per million (ppm) in 1959 to 427.35 ppm in 2025. The WMO reports that in 2024 CO₂ reached its highest level in the last 2 million years and methane and nitrous oxide their highest in at least 800,000 years, and that 2024's CO₂ increase was the largest since modern measurements began in 1957, driven by fossil-fuel emissions and weaker land and ocean carbon sinks.

The IPCC's Sixth Assessment Report concludes that human activities, principally through emissions of greenhouse gases, have unequivocally caused global warming, with global surface temperature 1.1 °C above 1850–1900 in 2011–2020. NASA quotes the IPCC: the human influence on warming has evolved from theory to established fact since systematic assessments began in the 1970s.

Scientists have many ways to check the climate.

Satellites look at Earth from space. Instruments measure the sea, even deep down. Old ice holds tiny bubbles of air from long ago. All of them show the same thing.

Scientists do not rely on one measurement. They use thermometers on land and at sea, satellites in space and instruments that measure the ocean far below the surface. To learn about the distant past, they study natural records: ice cores drilled from Greenland and Antarctica, tree rings, ocean mud, corals and layers of rock.

NASA says all these kinds of evidence show the signs of a changing climate. The ice cores are especially amazing: tiny bubbles of old air trapped in the ice tell scientists what the air was like long ago; NASA's ice-core record of carbon dioxide reaches back hundreds of thousands of years, so scientists can compare it with today.

Independent lines of evidence converge. NASA lists modern instruments, such as satellites and surface networks, alongside paleoclimate archives: ice cores from Greenland, Antarctica and tropical glaciers, tree rings, ocean sediments, coral reefs and sedimentary rocks. These show that current warming is roughly ten times faster than the average warming after an ice age, and that CO₂ from human activities is increasing about 250 times faster than it did from natural sources after the last ice age.

New indicators keep sharpening the picture. The WMO's 2025 report adds Earth's energy imbalance, the difference between the energy arriving from the Sun and the energy leaving Earth, as a key indicator for the first time. Under a stable climate the two are about equal; the imbalance has grown since records began in 1960, especially over the past 20 years, and reached a new high in 2025. Ocean heat content, measured to a depth of 2,000 m, has set a new record in each of the past nine years.

Most of the extra heat goes into the sea. The sea gets warmer.

Ice near the poles and on mountains is melting. Melting ice and warmer water make the sea level rise a little.

Where does the extra heat go? The WMO says more than 91 percent goes into the ocean. Only about 1 percent warms the air near the ground, where we feel it. About 3 percent melts ice.

The ice is shrinking in many places. NASA measured that from 1993 to 2019 Greenland lost an average of 279 billion tons of ice each year and Antarctica about 148 billion tons. Glaciers are retreating almost everywhere. In 2025, Arctic sea ice over the year was the lowest or second lowest since satellite records began. Melting ice and warming ocean water are making the sea rise: in 2025, global sea level was about 11 centimeters higher than in 1993.

The WMO's energy accounting: more than 91 percent of the excess heat is stored in the ocean, about 5 percent in the land, about 3 percent in warming and melting ice and about 1 percent in the atmosphere. Ocean heat content to 2,000 m reached a record in 2025; its rate of increase in 2005–2025, about 11.0–12.2 zettajoules a year, is more than double that of 1960–2005, roughly 18 times humanity's annual energy use. About 90 percent of the ocean surface experienced at least one marine heatwave in 2025. The ocean also absorbs CO₂; NASA notes that surface ocean acidity has increased by about 30 percent since the Industrial Revolution.

Ice is responding. NASA's GRACE data show average losses of 279 billion tons a year from Greenland and 148 billion from Antarctica between 1993 and 2019, and glaciers are retreating in the Alps, Himalayas, Andes, Rockies, Alaska and Africa. The WMO reports that annual Arctic sea-ice extent in 2025 was the lowest or second lowest in the satellite era and Antarctic extent the third lowest. Global mean sea level in 2025 was about 11 cm above 1993, the start of satellite altimetry, and its rise has accelerated.

A warmer world can change the weather.

Some places get more very hot days. Some get heavier rain. Weather scientists warn people early, so they can stay safe.

A warmer climate changes the weather people live with. The IPCC, a large group of scientists who review climate research for the world's governments, says human-caused climate change is already affecting many kinds of extreme weather in every region of the world, such as heatwaves and very heavy rain.

The WMO reported that in 2025, intense heat, heavy rainfall and tropical storms caused disruption in many places. That is why weather services are working to make sure everyone can get early warnings, so people have time to prepare and stay safe.

The IPCC's Synthesis Report (2023) states that human-caused climate change is already affecting many weather and climate extremes in every region across the globe, leading to widespread adverse impacts and losses for nature and people, with vulnerable communities that have contributed least to the problem disproportionately affected. It projects that every increment of warming will intensify multiple and concurrent hazards.

The WMO's 2025 report documents extreme heat, heavy rainfall and tropical cyclones around the world, and includes a chapter on climate and health, covering heat stress and the spread of dengue. Adaptation is part of the response: the IPCC finds that adaptation planning has progressed in all sectors and regions, although gaps remain, and the WMO co-leads the United Nations initiative Early Warnings for All, which works to strengthen warning systems in every region.

People all over the world are working on this problem.

Scientists keep measuring and sharing what they find. Countries have agreed to work together. Energy from the Sun and wind has become much cheaper, and people are using much more of it.

There is a lot of work going on. Scientists in many countries share their measurements so everyone can see what is happening. In 2015, countries meeting in Paris adopted the Paris Agreement, which aims to keep warming well below 2 °C and to try to limit it to 1.5 °C.

Clean energy has grown fast. The IPCC found that from 2010 to 2019, the cost of solar power fell by 85 percent, wind power by 55 percent and the batteries used in electric cars by 85 percent, while the use of solar power grew more than ten times. Scientists say that cutting greenhouse gases quickly and steadily would slow the warming noticeably within about 20 years. People have solved a big shared problem before: after British scientists discovered the ozone hole, countries signed the Montreal Protocol in 1987, and the ozone layer is slowly recovering.

The IPCC finds that limiting warming requires reaching net zero CO₂ emissions, and that deep, rapid and sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global warming within around two decades, and to discernible changes in atmospheric composition within a few years. Its assessment shows the tools improving: from 2010 to 2019 the unit costs of solar energy fell 85 percent, wind 55 percent and lithium-ion batteries 85 percent, while deployment rose more than tenfold for solar and more than a hundredfold for electric vehicles.

The Paris Agreement, adopted on 12 December 2015 and in force since 4 November 2016, aims to hold warming well below 2 °C above pre-industrial levels and to pursue efforts to limit it to 1.5 °C; countries submit updated national climate plans every five years. The IPCC also notes that pledges announced by October 2021 would make it likely that warming exceeds 1.5 °C this century, so the size and speed of cuts this decade matter. Precedent exists: the British Antarctic Survey's discovery of the ozone hole led to the 1987 Montreal Protocol, and recovery is under way, with full repair expected around 2070.