Every fact in the three climate lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/s² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the lessons simplify: the warming figures depend on the baseline: the IPCC compares 2011–2020 with 1850–1900 (about 1.1 °C), while NASA's 2025 figure (1.19 °C) is compared with 1951–1980, so the two numbers cannot be compared directly. The CO₂ values in the 15–16 lesson mix a March value (1958) with May peaks (2025, 2026); because of the seasonal cycle this slightly changes the calculated rate. The jar 'greenhouse' for ages 6–7 mostly works by stopping warm air from mixing with the room, which is how a real greenhouse works but not exactly how greenhouse gases trap heat; the lesson says it is 'a bit like' the real effect. The ice-melting model for ages 10–11 uses fresh water and ice cubes; in the real ocean the salt water makes a very small difference that the lesson leaves out. The lessons follow the IPCC, NASA and the Met Office and do not discuss policy choices.
All sources
[1] What is climate?
Met Office (UK national weather service) · Reliability: High
Type: National weather service education page
Weather occurs over hours or days; climate is the general weather over a long period; a region's climate is usually defined over a period of 30 years and can include rainfall, temperature, snow or any other weather condition, for example how often the temperature exceeds 30 °C in a place.
[2] What is the difference between weather and climate?
European Space Agency (ESA) · Reliability: High
Type: Space agency education page
The difference between weather and climate is a matter of time: weather refers to the short-term conditions of the atmosphere, climate describes the average weather conditions over a long period of time.
Met Office (UK national weather service) · Reliability: High
Type: National weather service education page
Köppen groups: tropical, dry, temperate, continental and polar; climate zones are divided by latitude, and also depend on distance from the sea, altitude, winds and currents; tropical climates near the equator have high temperatures and rainfall, rainforests have year-round rain; dry climates (deserts) are extremely dry with large day–night temperature swings; temperate: coldest month between 0 °C and 18 °C and at least one month above 10 °C; continental: greater temperature extremes in continental interiors; polar: no month above 10 °C; ice cap: no month above 0 °C, also at great altitude; tundra: warmest month 0–10 °C, no trees but dwarf shrubs and grasses.
Certain gases in the atmosphere trap heat from the Sun, similar to how a glass greenhouse keeps plants warm; sunlight passes through the atmosphere and warms Earth's surface, which releases the heat, and some of it is held in by the gases; this keeps Earth warm enough to support life as we know it.
The greenhouse effect is the warming that results when the atmosphere traps heat radiating from Earth toward space; key greenhouse gases are carbon dioxide, methane, nitrous oxide, chlorofluorocarbons and water vapour (water vapour increases as the Earth warms, a feedback); burning fossil fuels like coal and oil has increased CO₂, and clearing land also contributes; industrial activities have raised atmospheric CO₂ by nearly 50% since 1750; the IPCC concluded that the increase in CO₂, methane and nitrous oxide is unequivocally due to human activities.
Earth's average surface temperature has risen about 1 °C (2 °F) since the late 19th century; the top 100 m of the ocean warmed by 0.33 °C since 1969; Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019 and Antarctica about 148 billion tons per year; global sea level rose about 20 cm in the last century, and the rate in the last two decades is nearly double that; Arctic sea ice extent and thickness have declined rapidly; glaciers are retreating almost everywhere; Northern Hemisphere spring snow cover has decreased; the acidity of surface ocean water has increased by about 30% since the Industrial Revolution.
Average global temperature has increased by a little more than 1 °C since 1880; two-thirds of the warming has occurred since 1975; 2024 was the hottest year since records began in 1880; 2025 was 1.19 °C above the 1951–1980 average; the last decade is the warmest in all five records compared; human emissions of heat-trapping greenhouse gases are making the planet warmer.
[8] Annual Carbon Dioxide Peak Reaches 432 Parts per Million
Scripps Institution of Oceanography, UC San Diego (with NOAA) · Reliability: High
Type: University research news (Keeling Curve, Mauna Loa)
CO₂ at Mauna Loa peaked at 432.00 ppm in May 2026, 1.8 ppm above the May 2025 value of 430.2 ppm; Charles David Keeling began measurements in 1958, with an initial measurement of 313 ppm on 29 March 1958; CO₂ peaks in May, falls during the Northern Hemisphere growing season and rises again in autumn as vegetation dies back.
[9] AR6 Synthesis Report: Summary for Policymakers
Intergovernmental Panel on Climate Change (IPCC) · Reliability: High
Type: International scientific assessment (UN body)
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; global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018; in 2019 CO₂ concentrations (410 ppm) were higher than at any time in at least 2 million years; every increment of global warming will intensify multiple and concurrent hazards; limiting human-caused warming requires net zero CO₂ emissions; choices and actions in this decade will have impacts now and for thousands of years.
NASA My NASA Data, Langley Research Center · Reliability: High
Type: Space agency classroom lesson plan
As ice sheets and glaciers melt, the water eventually runs into the ocean, causing sea level to rise; icebergs and frozen seawater also melt in warm temperatures but do not cause sea level to rise; classroom model: put ice cubes in a container, fill it with water and observe the water level as the ice melts.
National Snow and Ice Data Center (NSIDC), University of Colorado · Reliability: High
Type: University / government-funded data centre education page
If the Greenland Ice Sheet melted entirely, sea level would rise about 7.4 m; if the Antarctic Ice Sheet melted, about 60 m; the two ice sheets make up the vast majority of Earth's land ice; sea level rise is caused primarily by meltwater from glaciers and ice sheets together with thermal expansion of seawater.