This is the world's temperature, year by year, since 2000. It is not a smooth line. Some years jump; some fall back. 2016 was hot; 2018 was cooler. Yet the ten warmest years ever measured are the last ten. The wobble is the weather. The slope is the climate.
2016, an El Niño year1.3°C
2018, the Pacific cool again1.1°C
Warmer than the late 1800s.
Why does it wobble? The biggest reason is the Pacific Ocean. Every few years its surface warms for a year and hands heat to the air; people call this El Niño. Then it cools again. 2016 and 2023 to 2024 were El Niño years. The ocean is moving heat around. It is not making new heat.
20161.3°C
20181.1°C
20241.6°C
Warmer than the late 1800s.
2018 was cooler than 2016. Does that mean the world stopped warming?
No. One cooler year is the wobble. The slope is read over decades.
Right. By 2024 the next El Niño arrived on a higher floor and set a new record. One year down, then a bigger year up, is what a climbing line with a wobble looks like.
Yes. A fall is a fall.
Not yet. By that rule the world also stopped warming in 1999, 2008 and 2011, and it did not. A single year cannot show a slope; two years cannot either.
It shows the warming went into reverse for two years.
Not yet. It shows the Pacific handed back less heat that year. The climb in the background did not pause. The next El Niño started from a higher point than the last one.
0°C0.59°C1.18°C
1900s2010s
Each decade's average, rounded.
Take each decade's average instead of each year. The wobble mostly vanishes and you can see the slope: flat until about 1970, then climbing about 0.2 degrees every ten years. Scientists say climate means about thirty years of weather averaged together, long enough for the Pacific to swing both ways several times.
A made-up record: a steady climb with a wobble laid on top. Move the control to change how many years are averaged together before the line is drawn.
0°C0.78°C1.57°C
20022024
A made-up record: a steady climb with a wobble on top.
one yearSingle years. The line falls 5 times in eleven steps, once by 0.5°C. Pick the right two years and you can argue it is cooling.
0°C0.67°C1.34°C
20022024
A made-up record: a steady climb with a wobble on top.
3 yearsAveraged over 3 years. Less jumpy: it falls 4 times, by up to 0.2°C. The climb shows, but a cool patch can still hide it.
0°C0.56°C1.12°C
20022024
A made-up record: a steady climb with a wobble on top.
10 yearsAveraged over 10 years. The line no longer falls at all, though it still climbs unevenly.
0°C0.45°C0.9°C
20022024
A made-up record: a steady climb with a wobble on top.
30 yearsThirty-year averages. The wobble is gone. The line never falls; only the climb of about 0.2 a decade is left.
Which window lets you read the slope?
Three years. Long enough to smooth it, short enough to be up to date.
Not yet. Better than one, but a cool patch of three years can still sit below the last patch. The Pacific's swings last about that long, so three years can still be all wobble.
One year. It shows the most detail.
Not yet. It shows the most wobble. Detail is not the slope; it hides the slope. With single years you can pick a start and an end that make a climbing line look flat.
Thirty years. The wobble averages out and only the climb is left.
Right. That is why thirty is the number scientists use. It is long enough for the Pacific to swing both ways several times, so no single swing can pass for a trend.
Move the control.
Which of these is weather, and which is climate?
One card at a time. Tap the pile it belongs to.
Card 1 of 6
It snowed in Madrid in January.
Madrid's Januaries are about 1.5°C warmer than in the 1960s.
Last winter was the coldest in ten years.
The last ten years are the ten warmest on record.
A hurricane hit Florida on Tuesday.
The sea off Florida has warmed about 1°C since 1900.
It snowed in Madrid in January. → Weather
Not yet. This is weather. It is one thing that happened on one day in one city.
Madrid's Januaries are about 1.5°C warmer than in the 1960s. → Climate
Not yet. This is climate. It compares many Januaries over sixty years, which is a pattern, not a day.
Last winter was the coldest in ten years. → Weather
Not yet. This is weather. One season is one event. A cold winter still happens in a warming world.
The last ten years are the ten warmest on record. → Climate
Not yet. This is climate. Ten whole years against every year measured is the pattern across decades.
A hurricane hit Florida on Tuesday. → Weather
Not yet. This is weather. A hurricane on a Tuesday is one event with a date on it.
The sea off Florida has warmed about 1°C since 1900. → Climate
Not yet. This is climate. A change over more than a century is the long pattern, not one storm.
One day, one seasonweather
vsvs
Thirty years of them, averagedclimate
Right. Weather is one event or one season. Climate is the pattern across decades. A cold winter still happens in a warming world. It happens less often than it did.
Of the ten warmest years ever measured, how many fall in the last ten years, 2015 to 2024?
Pick one. Nothing is scored.
10 of 10
of the ten warmest years fall in 2015 to 2024
All 10.This is the wobble and the slope together. Even the coolest recent year sits above every year before 2015. A cold winter in your town does not move that list; only the whole planet, averaged, can.
The whole planet1.2°C
Land only1.7°C
The Arctic3°C
Warmer than the late 1800s, rounded.
One more trap: your town is not the world. The world's average includes the oceans, which warm slowly. Land warms faster, about 1.7°C so far. The Arctic faster still, near 3°C. So a place can be well ahead of the world's number, or, for a season, well behind it.
A headline reads: coldest April in thirty years hits Britain. What can you say from it?
It cannot happen in a warming world.
Not yet. It can and it does. Warming makes cold Aprils rarer, not impossible. The record is still made of wobbles, and some of them point down.
It is weather. It says nothing either way about the slope, which is read over decades and over the whole planet.
Right. One month, one country. Britain's own thirty-year averages have risen; this April sits inside the spread around them, at the cold end. Next April will most likely sit nearer the middle.
The warming has stopped, at least in Britain.
Not yet. A single month in one country is one wobble. Britain's thirty-year average April is warmer than it was; one cold April below it is what a spread looks like.
Lesson complete
Weather is one year's wobble. Climate is the slow line the wobbles sit on.