The air: days→The sea surface: years→The deep sea: centuries→The ice sheets: thousands of years
Different parts of the planet answer at different speeds. The air changes in days. The sea surface takes years. The deep sea takes centuries to feel a change at the top. The great ice sheets of Greenland and Antarctica take thousands of years. When the air stops warming, the slow parts are still catching up.
Warming held at 1.5°C2.5 metres
Held at 2°C4 metres
Held at 5°C20 metres
Sea level rise over 2,000 years, midpoints of the panel's ranges.
Look at the sea. Even if warming were held at 1.5 degrees from now on, the heat already at the surface keeps sinking into the deep water for centuries, swelling it as it arrives, and ice already melting keeps melting. The climate science panel puts the rise at 2 to 3 metres over the next 2,000 years.
Rise so far, since 19000.21 metres
Rise over 2,000 years if held at 1.5°C2.5 metres
Warming stops at 1.5 degrees. Over the next 2,000 years, what does the sea do?
Keeps rising, by about 2 to 3 metres, as the deep sea and the ice catch up.
Right. The air stopped. The sea and the ice had barely begun to answer, and they answer for centuries. That is ten times the rise of the last hundred years, from warming that has already happened.
Falls back to where it was.
Not yet. Nothing takes the heat back out of the deep sea for thousands of years, and ice that has melted needs thousands of years of cold to grow back. Falling back is not on the list of things that happen.
Stops rising the same year the warming stops.
Not yet. The air stops fast because it is small. The deep sea is still taking heat that reached the surface decades ago, and it swells as it takes it. Ice melts for as long as it is warmer than it was.
Emissions reach zero→The bath stops filling→The air stops warming within decades→It holds there for centuries
The air, though, is quick. Cut emissions to zero and the air's temperature stops rising within a few decades and holds roughly where it is. It does not fall back much, because what is in the bath stays in the bath. So each tonne we add sets the temperature the air will stop at.
Move the control to set the year emissions reach zero, cut in a straight line from today's 40 billion tonnes. Each 1,000 billion tonnes adds about 0.45 degrees, the rule scientists use.
Warming so far1.2°C
Where the air's warming stops1.2°C
2030Zero by 2030: about 100 billion more tonnes go in first, and the air stops warming at about 1.2°C.
Warming so far1.2°C
Where the air's warming stops1.4°C
2050Zero by 2050: about 500 billion more tonnes go in first, and the air stops warming at about 1.4°C.
Warming so far1.2°C
Where the air's warming stops1.6°C
2070Zero by 2070: about 900 billion more tonnes go in first, and the air stops warming at about 1.6°C.
Warming so far1.2°C
Where the air's warming stops1.9°C
2100Zero by 2100: about 1,500 billion more tonnes go in first, and the air stops warming at about 1.9°C.
Reaching zero by 2050 instead of 2100 changes where the air's warming stops by about how much?
Nothing. The air stops when emissions stop, at the same level either way.
Not yet. It stops when emissions stop, but where it stops depends on how much went into the bath first. Fifty more years of pouring is a fuller bath and a warmer stop.
About 2 degrees, for fifty extra years of emissions.
Not yet. The tap is closing over those years, so the extra is a triangle, not fifty full years. About 1,000 billion tonnes, which is about half a degree.
About half a degree: 1.45 instead of 1.9.
Right. Fifty more years of a closing tap is about 1,000 billion more tonnes, and 1,000 billion tonnes is about 0.45 degrees. The date sets the total poured in, and the total sets the stopping point.
Move the control.
Emissions stop. Which of these stops within decades, and which keeps going for centuries?
One card at a time. Tap the pile it belongs to.
Card 1 of 5
The rise in air temperature
The rise in sea level
The shrinking of Greenland's ice
Hot summers getting more common
The deep sea warming
The rise in air temperature → Stops within decades
Not yet. This stops within decades. Air is light and quick, so once the tap is off it settles in a few decades.
The rise in sea level → Goes on for centuries
Not yet. This goes on for centuries. The sea rises as deep water warms and ice melts, and both take hundreds of years to catch up.
The shrinking of Greenland's ice → Goes on for centuries
Not yet. This goes on for centuries. An ice sheet is heavy and slow, and it keeps shrinking long after the air stops warming.
Hot summers getting more common → Stops within decades
Not yet. This stops within decades. Hot summers follow the air's temperature, and the air settles within decades.
The deep sea warming → Goes on for centuries
Not yet. This goes on for centuries. The deep sea has enormous mass, and heat takes hundreds of years to reach the bottom.
The airstops within decades
vsvs
Water and icekeep going for centuries
Right. The fast list is everything the air does. The slow list is everything with a lot of mass, water and ice, which takes centuries to catch up. A person can live to see the first list stop. Nobody lives to see the second.
If all of Greenland's ice melted, how much would the sea rise?
Pick one. Nothing is scored.
Greenland7 metres
Antarctica58 metres
Sea level rise if all of it melted.
About 7 metres.The number people remember, 60 metres, is Antarctica. Greenland alone is about 7. Neither happens in a lifetime. Both are already losing ice, and as a great sheet shrinks its top sits lower and warmer, so it melts faster still.
Ice melts→Dark sea and rock are bared→More sunlight is soaked up→It gets warmer→More ice melts
Some slow parts push themselves along. Melting ice bares dark rock and sea, which soak up more sun, which melts more ice. Thawing frozen ground lets ancient plants rot and give off carbon, which warms the air, which thaws more ground. Scientists call a loop like this a feedback: the change feeds its own cause.
A country reaches zero emissions in 2050, and its capital sits by the sea. Which is true for the people living there in 2150?
The sea stopped rising in 2050 with the emissions.
Not yet. The sea does not read the emissions figures. It reads the heat already in the deep water and the ice already melting, and both of those keep going for centuries after the tap closes.
The air has held about level for a century, and the sea outside is still rising.
Right. The fast part stopped and the slow parts did not. Sea walls built in 2050 to the 2050 tide are the kind of thing the people of 2150 inherit.
Both the air and the sea have gone back to where they were in 1900.
Not yet. Neither goes back. The bath stays full, so the air holds where it stopped; the deep sea and the ice are still catching up to a warming that ended a century before.
Lesson complete
Air temperature can stop rising within decades of emissions stopping. The sea and the ice keep moving for centuries.