Earth has warmed before. What's different this time?
The planet was once nearly frozen over, and once had no permanent ice at either pole. Those past shifts don't disprove today's warming; they give us the data to understand what happens when Earth's energy balance changes.
"The climate has always changed" isn't wrong - it just answers the wrong question. Three better questions: how fast is the temperature changing, what's causing it, and how much time do people and ecosystems have to adapt?
01 · Reading the planet's memoryWithout thermometers, how do we know the past was hot or cold?
The global network of thermometers is only dense enough from the late 19th century onward. For anything further back, scientists read the traces climate leaves behind: air bubbles trapped in ice cores that preserve samples of ancient atmosphere; isotope ratios in ice, marine shells and stalagmites that track with temperature; tree rings that record growing seasons; pollen, coral and sediment that reveal what the environment looked like at the time.
Each proxy has its own error margin and resolution. Ice cores read the last few hundred thousand years very well; marine sediments reach back tens of millions of years but more faintly. Science doesn't stitch together one temperature line from a single measurement: independent records are cross-checked, dated, calibrated, and compared against physical models.
02 · The physical mechanismWhy does more CO₂ make Earth warmer?
Sunlight reaching Earth arrives mostly at short wavelengths (visible light), passes through the atmosphere with little resistance, and warms the ground and oceans. The warmed surface radiates energy back - but at much longer wavelengths, in the infrared, because cooler objects emit energy at longer wavelengths. If the atmosphere were completely transparent to infrared, most of that energy would escape straight into space and Earth's surface would be about 33°C colder than it is today.
CO₂, water vapor and methane aren't transparent that way. Their molecular structure - how their atoms vibrate and bend - makes them absorb exactly the infrared wavelength bands the ground emits, then re-radiate that energy in all directions, including back down. Some of the heat that would otherwise have escaped into space is therefore held near the surface longer. Nitrogen and oxygen - more than 99% of the atmosphere - barely participate in this effect, because their symmetric molecular structure doesn't absorb infrared this way.
Light in short, heat out long - some of it gets trapped
03 · An ice-core timelineThe times Earth's state has flipped
Drag the ice-core bar on the left - or tap each marker - to scrub through seven times Earth's state has flipped.
"Snowball Earth": a planet nearly frozen solid
Continents sat in the tropics, weathering pulled down CO₂, and ice-albedo feedback created a self-amplifying freeze. Volcanoes kept pumping CO₂ while weathering was locked away by ice; the greenhouse gas that eventually built up helped melt the ice away. Whether the ocean froze completely or kept open bands of water is still debated.
PETM: a massive carbon pulse
The PETM (Paleocene-Eocene Thermal Maximum) was a sudden warming episode at the boundary between the Paleocene and Eocene epochs. A huge amount of carbon entered the atmosphere and ocean over a few thousand years, raising global temperatures roughly 5-8°C and acidifying the ocean. The original carbon source is still being studied; volcanism in the North Atlantic, methane, and carbon-cycle feedbacks may all have contributed. Many deep-sea species went extinct, while climate zones and organisms shifted toward the poles.
Eocene: a greenhouse with no permanent polar ice
CO₂ was high, forests grew at very high latitudes, and sea levels were far higher. As CO₂ fell over the long run through weathering, carbon burial, and shifts in tectonics and ocean currents, Antarctica began growing a major ice sheet around 34 million years ago.
The Ice Ages: an orbital rhythm amplified by CO₂ and ice
Orbital eccentricity, axial tilt and precession redistribute sunlight by season. A small signal in Northern Hemisphere summers lets ice advance or retreat; albedo and CO₂ released from the ocean turn it into a global-scale shift. The most recent cold peak was around 20,000 years ago, when global temperature was roughly 5-6°C below the pre-industrial level.
Deglaciation, then the Younger Dryas cold snap
Earth warmed gradually as orbital changes strengthened Northern Hemisphere summers. A large pulse of fresh water into the North Atlantic may have weakened ocean circulation, plunging the North Atlantic region back into cold for nearly 1,200 years. This was a very sharp regional swing riding on top of a global-scale transition.
The Medieval Climate Anomaly and the Little Ice Age
Warm and cold periods were out of phase from region to region, not synchronized worldwide. Some regions - especially the North Atlantic - were warm in medieval times; the following period turned colder because of a cluster of volcanic eruptions, weaker solar output, and ice-ocean feedbacks. The coldest point occurred at different times in different places.
The industrial era: a new driver rising in a near-vertical line
Burning coal, oil and gas; cement production; deforestation have pushed CO₂ from about 280 ppm to over 420 ppm. Greenhouse gases warm the planet; industrial aerosols mask part of that warming. Since around 1970, the greenhouse signal has overwhelmed natural variability in the multi-decadal trend.
04 · When history books meet ice coresFrom the Common Era onward: how has extreme climate made it into the historical record?
From roughly the year 1 CE onward, we can lay two kinds of evidence side by side: natural proxies and human records - chronicles of a dimmed sky, frozen rivers, prolonged rain, grain prices, crop failures, migration and death. Together they make climate very concrete, but also easy to over-interpret.
Drag or tap the year markers below to flip through each record, from 536 to today.
"The sun gave forth its light without brightness": a volcanic shock at the end of antiquity
Procopius wrote in 536 that the sun shone weakly "like the moon"; Cassiodorus described people's shadows failing to show clearly at noon. Ice cores and tree rings confirm major eruptions in 536, 540 and 547, producing unusually cold summers across much of the Northern Hemisphere. Researchers still debate whether the cold phase lasted until roughly 660 or mostly ended in the 570s.
The millennium's largest sulfate spike
Samalas on the island of Lombok erupted roughly 40 km³ of dense-rock-equivalent magma and drove sulfur into the stratosphere. Ice cores at both poles preserve the sulfate spike; documentary sources and tree rings show the summers of 1258-1259 among the coldest in the Northern Hemisphere in 1,000 years.
Three years of relentless rain drowned the harvest
Persistent rain from 1314 to 1316, cool summers and waterlogged soil kept grain from ripening, hay from drying, and salt from being produced. Hydroclimate reconstructions rank these three summers among the fifth-wettest three-year stretch in 700 years in the European regions studied.
Cold in pulses, not synchronized worldwide
Clusters of eruptions, periods of weaker solar output, and sea-ice-ocean feedbacks contributed to colder conditions in many regions. The Thames hosted frost fairs on the ice, Alpine glaciers advanced onto farmland; China recorded repeated droughts, floods and cold spells. The coldest point differed from continent to continent.
1816: the "Year Without a Summer"
Tambora in Indonesia erupted in April 1815. Sulfate aerosols cooled the Northern Hemisphere the following year by roughly 0.5°C; New England saw frost in midsummer, Western Europe turned cold and wet, and the Asian monsoon was disrupted.
An extreme El Niño meets unusual oceans
Multi-year droughts struck India, northern China, northeastern Brazil, and much of Africa simultaneously. The mechanism was a rare combination: a prolonged cold Pacific beforehand, the very strong 1877-1878 El Niño, an extreme Indian Ocean Dipole, and a warm North Atlantic.
From short-lived shocks to a shifting baseline climate
The Dust Bowl, the Sahel drought, the 2003 European heatwave, the 2010 Russian heatwave, and recent heat events have all been directly measured. Attribution science now asks a different question: how much has the new climate shifted the probability and intensity of an event, rather than labeling any single event as simply "caused" by warming or not.
History shows two things. First, just a few tenths of a degree at hemispheric scale can upend a harvest if cold, heat or rain arrives at the wrong moment. Second, the same weather shock can lead to wildly different outcomes: forecasting, stockpiles, trade and relief determine whether a bad harvest turns into a famine.
The butterfly effect: why do we understand climate but can't say exactly which day it will rain?
The butterfly effect is the popular name for "sensitivity to initial conditions" in a chaotic nonlinear system. It doesn't say that every small event is bound to cause a giant catastrophe. It says that two nearly identical starting states can diverge onto very different trajectories given enough time, so even a tiny measurement error sets a limit on how far ahead detailed forecasting can reach.
0.506127 became 0.506
Meteorologist Edward Lorenz reran a simple weather model partway through. He typed in 0.506, the number printed on paper, instead of the machine's stored value of 0.506127 - a difference of about 0.025%. The two runs tracked closely at first; after many iterations, they diverged into completely different outcomes. His 1963 paper laid the foundation for chaos theory; the title of his 1972 talk turned it into the image of a "butterfly flapping its wings in Brazil, a tornado in Texas."
51 future scenarios, run in parallel
ECMWF generates many forecasts with slightly different starting conditions and models. If the 51 scenarios cluster together, confidence is high; if they fan out widely, the forecast is uncertain. That's why a bulletin gives a probability of rain, or a hurricane-track "cone," instead of a single certain future path.
So invoking the butterfly effect to dismiss climate models misapplies the idea. Weather asks about the exact state of the atmosphere on a given day; climate asks about the statistics of a huge number of states - averages, ranges, and the probability of extremes - under energy constraints. We don't know heads or tails on the 10,001st coin flip, but we can still forecast the ratio across a million flips.
05 · Same heat, different speedPETM and today: the most unsettling comparison
The PETM is often called an "analogue" for modern climate change because both involve a rapid carbon pulse by geological standards. But analogue doesn't mean identical: continental configuration, baseline climate, and carbon source all differ. The value of the PETM is showing how the system responds when carbon rises - warming, ocean acidification, shifting habitats, and selective extinction.
Today is many times faster than the estimated PETM pulse
Order-of-magnitude comparison; PETM estimates carry considerable uncertainty. GtC = gigatons of carbon, not CO₂.
The PETM raised temperatures 5-8°C, but over thousands of years. Today, in barely a century, warming has already reached about 1.4°C at the recent annual level. Speed matters because forests, coral reefs, agriculture, cities and coastal infrastructure can't simply "migrate" along an isotherm.
Slow onset, large feedbacks
- Orbital shifts play out over tens of thousands of years.
- Tectonics and weathering run on million-year timescales.
- Large eruptions can pump carbon over the long term; sulfate plumes cause short-term cooling.
- CO₂ often acts as both a feedback and an amplifier that sustains change.
Forcing the system with fossil carbon
- CO₂ has risen more than 50% since pre-industrial times.
- Carbon and oxygen isotope signatures confirm the source is burned fossil carbon.
- The lower troposphere warms while the stratosphere cools - a greenhouse "fingerprint," not a solar one.
- The ocean is gaining heat, ice is being lost, and sea level is rising, all at once.
06 · From 1900 to 2025A century that didn't warm in a straight line
Year-to-year noise, a long-term trend
1900-1940: early warming
Greenhouse gases rose, while the sun and internal variability both contributed. Some regions - especially the Arctic - warmed noticeably. Early-century data is sparser but has been adjusted for changes in how land and sea measurements were taken.
1940-1970: the temperature line stalls
Coal and industry emitted not just CO₂ but also sulfate aerosols that reflect sunlight and brighten clouds. Aerosols, together with ocean variability, masked part of the greenhouse effect. After clean-air laws in the U.S. and Europe, aerosols declined while CO₂ kept accumulating; temperatures rose clearly from the 1970s onward.
1970-present: multiple "fingerprints" line up
It isn't just surface thermometers: the ocean has absorbed more than 90% of the excess heat; the troposphere is warming while the stratosphere cools; nights are warming faster than days; sea ice, glaciers and both ice sheets are losing mass; sea level is rising and the rate is accelerating. Any alternative hypothesis that explains only surface temperature but not this whole set of fingerprints isn't sufficient.
07 · Stress-testing the counterargumentsConspiracy theories, skepticism, and popular alternative hypotheses
Skepticism is part of science when it offers a mechanism and a test. Conspiracy thinking does the opposite: every piece of contradicting data gets reinterpreted as evidence of a deeper conspiracy. Below is the strongest version of each argument, not a mocking caricature.
Half right, wrong conclusion"Climate has always changed naturally; this is no different."
The premise holds up. The problem is the next step: natural causes have measurable signatures and rhythms. Earth's orbit currently leans toward a very slow cooling trend; solar variability hasn't risen enough; large eruptions typically cause 1-2 years of cooling. Models using only natural drivers can't reproduce the observed trend since the mid-20th century; adding human drivers, they match.
Doesn't match observations"It's the sun getting hotter, not CO₂."
If the sun were strengthening, the whole atmosphere would warm in a different pattern. Observations show solar output has had no sufficiently large trend since the late 1970s, while the lower atmosphere is warming and the stratosphere is cooling - exactly what's predicted when greenhouse gases trap heat below.
Cause and effect reversed"CO₂ lags temperature in ice cores, so CO₂ doesn't cause warming."
In glacial cycles, orbital changes are usually the initial trigger; a warming ocean releases CO₂, which then amplifies and spreads the change globally. A factor can be both a past feedback and a present-day forcing. This time, humans put the carbon in first, and temperature followed.
A real episode, but "the consensus" claim is a myth"Scientists in the 1970s predicted an ice age."
The mid-century did see a slowdown/slight cooling, and aerosols were a genuine concern at the time. But a review of 71 papers from 1965-1979 found 44 predicting warming, 20 neutral, and 7 predicting cooling. A famous magazine cover doesn't represent the balance of the research. Science since then has also better understood aerosols and greenhouse gases, not erased that history.
A real incident, but it doesn't overturn the evidence"Climategate proved the data was faked."
The 2009 hacked emails contained unflattering internal language and disputes over data transparency. Multiple independent investigations found no evidence that temperature conclusions were fabricated. More importantly, independent groups using different methods and data - NASA, NOAA, Hadley/CRU, Berkeley Earth, Copernicus, JMA - still show the same trend.
Wrong about scale and direction of impact"Volcanoes emit more CO₂ than humans do."
Human carbon emissions are more than 100 times larger than all modern volcanoes combined. Large eruptions send sulfate into the stratosphere and typically cause short-term cooling; human CO₂ accumulates and its effect lasts centuries to millennia.
Confuses weather with climate"We still get cold winters, so Earth isn't warming."
A cold snap only describes the weather at one place and one moment. Climate is the statistics of many decades over a wide area. A warmer world can still set cold records; what's changing is that extreme cold is becoming less frequent while extreme heat is becoming more frequent and more severe.
Common arguments on Reddit: where are they right, and where do they go wrong?
Discussions on r/climateskeptics, r/conspiracy, r/climatechange and r/conspiracytheories tend to repeat the arguments below. This list only catalogs recurring argument patterns; it doesn't represent all of Reddit, and upvote counts don't indicate whether a claim is right or wrong.
Pattern 01 · bad inputs, bad outputs"Climate models run too hot; modelers tune parameters to get the result they want."
The true part: models do have to parameterize certain processes and still carry large errors forecasting clouds, rainfall, or extremes at local scale. Some CMIP6 models have too-high climate sensitivity, so results can't be averaged mechanically across all of them.
Where the inference breaks: "imperfect" doesn't mean "useless" or "rigged." Hausfather and colleagues took published forecasts from 1970 to 2007 and compared them against data the original authors could not have known. Most forecasts matched observed warming well, especially once measured against the actual forcing that occurred rather than the emissions scenario originally assumed.
How to check for yourself: look at what quantity a model forecasts, at what scale, under what emissions scenario, and with what uncertainty range. A model can get the global temperature trend right while getting rainfall wrong for one province; the two aren't contradictory.
Reddit pattern 02 · "they're rewriting the past""NOAA/NASA lower old temperatures and raise new ones to manufacture warming."
The true core: raw data really is adjusted. Stations move location, change reading times, switch shelter and thermometer types; ocean measurement shifted from bucket sampling to ship intake to buoys. Splicing those segments together unadjusted would create fake jumps.
The wrong leap: "adjustments exist" doesn't prove "adjustments were made to create warming." NOAA's algorithm finds breakpoints by comparing a station against its neighboring network; both the method and the raw data are public. In some places adjustments warm the trend, in others they cool it. Independent groups using different pipelines still find similar trends; ocean, ice, and satellite records also don't depend on any single land-station network.
Self-check: compare raw vs. adjusted at the station level, read the metadata for when equipment changed, then look at the global result from multiple independent teams - don't pick one station with a large adjustment and treat it as representative of the whole planet.
Reddit pattern 03 · a true fact used outside its scope"CO₂ is plant food; more CO₂ just makes Earth greener."
The true core: CO₂ is a raw material for photosynthesis. Given enough water and nutrients, many C3 plants like rice, wheat and soybeans grow faster and use water more efficiently. Satellites do observe some CO₂-driven greening.
The wrong leap: a physiological benefit doesn't erase the radiative effect. Greenhouses are irrigated, fertilized, and kept at an optimal temperature; open fields also face heat, drought, floods, pests, and nitrogen shortage. C4 plants like corn respond less; higher biomass can come with lower protein, iron and zinc content. NASA has recorded 86% of land ecosystems becoming less efficient at absorbing the extra CO₂.
Self-check: ask "which plant, where, does it have enough water and nitrogen, is it yield or nutrition, and what temperature comes with it?" "CO₂ benefits plants" and "excess CO₂ makes climate riskier" can both be true at once.
Reddit pattern 04 · a narrow view of what counts as a test"There's no Earth B to run a controlled CO₂ experiment on, so anthropogenic warming has never been tested."
The true core: we can't run a randomized controlled trial on two Earths. Complex-systems science always has limits on attribution.
The wrong leap: a controlled experiment isn't the only path to evidence. CO₂'s infrared absorption is measured in the lab; satellites measure the spectrum of outgoing radiation; ground instruments measure downward radiation; carbon isotopes point to a fossil source; the ocean measures accumulated heat; volcanoes provide a "natural experiment"; models with and without human forcing let researchers test the fingerprint. A hypothesis is strong because many independent tests all point the same direction.
Self-check: test an alternative hypothesis against the whole fingerprint set - does it simultaneously explain a warming troposphere, a cooling stratosphere, warmer nights, ocean heat gain, and falling carbon-13?
Reddit pattern 05 · motive doesn't replace measurement"Climate scare was manufactured to push carbon taxes and control the population."
The true core: a carbon tax is a political choice, it has distributional effects, and it can be designed badly; greenwashing, lobbying, and subsidy grabbing are real risks. Opposing a specific policy isn't the same as opposing climate physics.
The wrong leap: finding a beneficiary doesn't prove they created the phenomenon. For the conspiracy to hold, dozens of independent measurement systems, rival nations, universities, insurers, navies, commercial satellites, and even internal oil-industry research would all have to coordinate to fake the same chain of fingerprints.
Self-check: separate three questions: is the climate warming; what's causing it; which policy is fair and effective. Evidence for question one doesn't automatically validate every answer to question three.
Reddit pattern 06 · conflating three different technologies"Contrails, cloud seeding, and geoengineering are all secretly chemtrails."
The true core: cloud seeding is real; contrails can turn into cirrus clouds and cause warming; solar geoengineering with aerosols is a genuine research topic. Governments and militaries have studied weather modification before, so demands for transparency are reasonable.
The wrong leap: A existing doesn't prove program B exists at global scale. Contrails form when hot, moist exhaust meets sufficiently cold, humid air; because the atmosphere has varying humidity layers, trails can vanish quickly or linger. Cloud seeding needs suitable clouds and aims to alter local rainfall; it doesn't generate energy or steer continental pressure systems. HAARP affects the ionosphere and has neither the power nor the mechanism to steer tropospheric weather.
Self-check: demand a physical chain of evidence - what substance, what concentration, which aircraft, what logistics, chain-of-custody samples, mechanism, and energy balance. A photo of a trail plus weather changing two days later is just correlation in time order.
Reddit pattern 07 · cherry-picking the right number, wrong quantity"The all-time heat record is Death Valley in 1913, so how is it hotter now?"
The true core: one station can hold an instantaneous temperature record for decades; the reliability of the 1913 Death Valley record itself is still debated.
The wrong leap: global warming is a change in the average and distribution of millions of measurements, not a contest to find one single highest point. A die weighted toward six can still have rolled a six before; the sign is that six comes up more often, not that a seventh face has appeared.
Self-check: compare the count of record-hot days against record-cold days across a large network over many decades; don't compare one local extreme against a global average anomaly.
Scientific hypotheses that have been, or are still being, tested
| Hypothesis | What it explains | Why it doesn't replace the main current cause |
|---|---|---|
| Solar cycles | Small variation on an 11-year cycle and longer. | No trend in output matches recent warming; the pattern by altitude is wrong. |
| Milankovitch cycles | Trigger glacial cycles over tens to hundreds of thousands of years. | Far too slow; the current orbital configuration actually favors gradual cooling absent human influence. |
| Cosmic rays-clouds | A cloud-seed-nucleation mechanism may exist under certain conditions. | No evidence it produces a large enough forcing or the right trend to explain the temperature record. |
| ENSO, AMO/PDO | Shuttles heat between ocean and atmosphere, producing warmer/colder years and decades. | Redistributes heat; doesn't explain the long-term heat gain of the whole Earth system. |
| Water vapor | A powerful greenhouse gas and an important amplifying feedback. | Water vapor is short-lived and controlled by temperature; CO₂ is the long-term "dial" that lets air hold more vapor. |
08 · The geography of riskWhere suffers least as the world warms?
There's no absolutely safe "climate bunker." A place with less extreme heat may instead face floods, wildfires, thawing permafrost, or rising food prices from crop failures elsewhere. Risk also varies within a single country: high ground, a stable water supply, and distance from low-lying coastline usually matter more than the name on your passport.
Where does everyone sit on the climate risk map?
"Low risk" on this map doesn't mean absolutely safe. Every region still carries its own list of hazards:
Northern Europe
Canada & the Great Lakes
New Zealand
Duluth & Buffalo (U.S.)
Uruguay
Patagonia (Chile · Argentina)
Within the U.S.: which states are relatively stable, and when branding runs ahead of infrastructure
The previous section only touched the U.S. through two cities (Duluth, Buffalo); at the state level, the picture is clearer. Climate Central scores the 48 contiguous states (excluding Alaska and Hawaii) across 5 risk categories - extreme heat, drought, wildfire, flooding, and lengthening mosquito season - and combines them into one index; FEMA also maintains its own National Risk Index dataset by county. Both show the same shape: the Northeast and Great Lakes region cluster in the lowest-scoring group.
| State | Why it's relatively stable | Remaining risk |
|---|---|---|
| Vermont | The fewest federally declared disasters in the country (45 since 1953); deep inland, no coastline. | Extreme heat is nearly the only major climate threat. |
| New Hampshire | 82% forest cover as natural buffer; fewer tornadoes and wildfires than most of the U.S. | Its short coastline still needs long-term planning for sea-level rise. |
| Massachusetts | Shares a sub-100 risk score with Vermont and New Hampshire on the Climate Central index. | Its Atlantic coastline still takes hurricanes and storm surge. |
| Minnesota | About 10,000 freshwater lakes; winter-response infrastructure already long in place. | Summers are getting hotter and more humid, and seasonal flooding is rising. |
| Wisconsin | Deep inland; many cities have already upgraded drainage systems and levees. | Wildfires are rare, but localized urban flooding still occurs. |
| Utah | Dry climate, high terrain shields it from tropical storms and major flooding. | Prolonged drought and wildfire remain the main concerns. |
At the city level, the story gets more specific and louder. The concept most widely attached to the "low risk, infrastructure not keeping pace" group is the "climate haven" - a name that emerged from a 2018 Guardian piece about Duluth and Buffalo, then was used by Buffalo's mayor to call his own city a "climate refuge" in 2019. Jesse Keenan, an urban researcher at Tulane often mistakenly credited with coining the phrase, says he never actually used the words "climate haven"; what he proposed in the New York Times that same year was "climate-proof Duluth" - a small but important difference between media branding and academic research. He also stresses that most climate migration will happen at the scale of nearby regions, not one wave relocating half the U.S. northward.
Where might actually benefit?
The clearest benefits, where they exist, concentrate at high latitudes and usually only in certain sectors. The IPCC notes that growing seasons have already lengthened and arable zones have shifted northward; if warming stays moderate, some crops like wheat could see higher yields in Northern Europe. Heating demand falls, hydropower potential rises in some places, and forests may grow faster in the short term.
But calling these countries "winners" would be misleading. The IPCC projects that agricultural gains in Northern Europe won't offset the continent's overall losses, and could disappear once global temperature passes roughly 2°C. Longer warm seasons also bring more pests, drought, wildfire, and ecosystem disruption. Canada and Russia gain more land crossing the temperature threshold for farming, but poor soil, missing infrastructure, thawing permafrost and wildfire mean this "new" land doesn't automatically become good farmland.
The 2018-2023 non-renewal rate ran roughly 4× normal
AIG, Allstate and State Farm stopped writing new policies in California starting in the first half of 2023; Farmers withdrew from Florida the same year. Hit hardest: Florida, Louisiana, Texas and California.
09 · What can be said with confidenceA lesson from the past: the climate system is more sensitive than any reassurance suggests
Earth will survive. The phrase "save the planet" is therefore slightly off-target: the risk is to a civilization built within the relatively stable Holocene climate - the coastlines, the growing seasons, the water supply, the power grid, the insurance, and the ecosystems people depend on.
Climate change contributes to some disasters, but isn't the cause of all of them; attribution science is careful to avoid reducing any single event to a slogan. It typically acts as a probability- or intensity-multiplier layered on other factors: planning, poverty, water management, deforestation, and building codes decide how far a weather extreme escalates into a major disaster.
Action doesn't require a perfect model either. Decisions are made across a range of risk: the exact amount of warming, cloud feedback, and ice-sheet speed still carry uncertainty; but the direction of the impact, the source of the carbon, and the direction of change are no longer a 50-50 question.
Sources and how to read the figures
- WMO, State of the Global Climate 2025 - 2025 temperature, 2024 CO₂, ocean heat, sea level and ice.
- IPCC AR6, Synthesis Report: Summary for Policymakers - 2011-2020 warming level, attribution, and the pace since 1970.
- IPCC AR6 WGI, Chapter 2: Changing State of the Climate System - paleoclimate, the Holocene, and the interglacial 125,000 years ago.
- IPCC AR6 WGI, Chapter 3: Human Influence on the Climate System - fingerprints, models with/without human forcing, and attribution ranges.
- Wikipedia, History of climate change science - the Fourier (1824), Tyndall (1859) and Arrhenius (1896) milestones.
- Feldman et al. (2015), Observational determination of surface radiative forcing by CO2 from 2000 to 2010, Nature - direct measurement of increased infrared radiation from CO₂ at two U.S. observation stations.
- NOAA Climate.gov, Hasn't Earth warmed and cooled naturally? - glacial cycles and the orbital-CO₂ relationship.
- NOAA NCEI, Paleoclimatology - proxies, ice cores, sediment, and ancient climate records.
- NASA Science, Why Milankovitch cycles can't explain current warming.
- NASA Earth Observatory, Global Warming - paleoclimate, current pace, and feedbacks.
- NASA Science, Volcanoes and climate change - comparing emissions and sulfate-driven cooling.
- NASA Science, How scientists measure global temperature - urban-heat-island adjustments and agreement across datasets.
- Peterson, Connolley & Fleck (2008), The Myth of the 1970s Global Cooling Scientific Consensus, BAMS.
- Zeebe, Ridgwell & Zachos (2016), Anthropogenic carbon release rate unprecedented during the past 66 million years, Nature Geoscience - comparing rate against the PETM.
- U.S. National Academies, Climate Change: Evidence and Causes - lines of evidence and common counterarguments.
- Büntgen et al. (2016), Cooling and societal change during the Late Antique Little Ice Age, Nature Geoscience - the 536-547 eruption sequence; see also the duration debate in Helama et al. (2017).
- Guillet et al. (2017), Climate response to the Samalas volcanic eruption in 1257, Nature Geoscience - ice cores, tree rings and documentary sources for 1257-1259.
- Slavin (2020), A quantitative hydroclimatic context for the European Great Famine of 1315-1317, Communications Earth & Environment.
- Brugnara et al. (2015), The "year without a summer" 1816, Climate of the Past; and NOAA, Mount Tambora explosively erupts in 1815.
- Singh et al. (2018), Climate and the Global Famine of 1876-78, Journal of Climate - the multi-continent drought, ocean mechanisms, and food consequences.
- Lorenz (1963), Deterministic Nonperiodic Flow, Journal of the Atmospheric Sciences - the mathematical foundation of sensitivity to initial conditions.
- ECMWF, Introduction to chaos, predictability and ensemble forecasts and Ensemble weather forecasting - how chaos gets turned into probabilistic forecasts.
- Sample of Reddit discussions (accessed 07/01/2026): Flawed Climate Models, Climate Model Predictions?, temperature adjustments, CO₂ is plant food, climate conspiracy theories and chemtrails/weather modification. These are sources for identifying arguments, not for scientific verification.
- Hausfather et al. (2020), Evaluating the Performance of Past Climate Model Projections, Geophysical Research Letters - testing older model forecasts against post-publication observations.
- NOAA NCEI, GHCN-Monthly: Temperature and Data Homogenization - the rationale, algorithm, and metadata behind station adjustments.
- NASA, Climate impacts on crop growth and Land ecosystems are becoming less efficient at absorbing CO₂ - the benefits and limits of CO₂ fertilization.
- IPCC AR6 WGII, Chapter 13: Europe - the risk gap between Northern and Southern Europe, and short-term gains for agriculture, forestry and hydropower in the north.
- IPCC AR6 WGII, Chapter 5: Food, Fibre and Other Ecosystem Products - shifting arable zones at high latitude and the limits of agricultural gains.
- IPCC AR6 WGII, Chapter 11: Australasia - flood, fire, sea-level and water-supply risk in Australia and New Zealand.
- Notre Dame Global Adaptation Initiative, ND-GAIN Country Index 2024 and Vulnerability ranking - comparing vulnerability and adaptive readiness across 191 countries.
- UNDP, Uruguay - Climate Change Adaptation - Uruguay's temperate location, political stability, and adaptation steps.
- Island Studies Journal, Climate Change in Chiloé (Chile) - stronger coastal storms and damage to aquaculture in Patagonia.
- Grist, Why "climate havens" might be closer to home than you'd think - an interview with Jesse Keenan on the origin of "climate haven" and "climate-proof Duluth."
- PBS NewsHour, Why these "climate haven" cities aren't yet ready for more extreme weather events - the Buffalo blizzard and Duluth flooding of 2023.
- Yale E360, How Climate Risks Are Putting Home Insurance Out of Reach - nationwide home-insurance non-renewal figures for 2018-2023.
- Levy Economics Institute of Bard College, A Premium Crisis - insurers withdrawing from California, Florida, Louisiana and Iowa.
- SafeHome.org, Climate Change Risk Index: Best and Worst U.S. States - Climate Central's "States at Risk" data, the 5 risk categories, and state scores.
- Hippo Insurance, Best States for Climate Change - ranking Vermont, New Hampshire, Utah, Wisconsin, Minnesota.
Temperature figures are anomalies relative to a baseline period, not the planet's absolute temperature. Ancient markers and PETM rates are estimated ranges, rounded to avoid false precision.
03 Discussion
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