Earth's five systems and how they affect each other

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Card

   Permafrost holds about 1,500 Gt of carbon (billion tonnes). The air holds about 900 Gt of carbon. Loop: warming thaws ground, microbes release carbon gas, the gas adds warming.

2. 1.

   Noah traces the loop. If 5% of the permafrost carbon is released, what share of the air's carbon is that, and what sign is the loop?

   • A positive loop; 75 Gt is about 83% of the air's carbon, nearly the whole of it
   • A positive loop; 75 Gt is about 8% of the air's carbon
   • A positive loop; 75 Gt is about 0.8% of the air's carbon, a trace of it
   • A negative loop; 75 Gt is about 8% of the air's carbon, since the gas cools the air

3. Three loops (+ adds to the change, - reverses it)

   Loop	Links
   A	warmer air + more evaporation + more water vapor + warmer air
   B	warmer air + more weathering - less CO2 in the air + warmer air
   C	warmer air + more thaw + more carbon gas + warmer air

4. 2.

   Bo counts the reversing links in each loop. Which loops amplify a change?

   • A, B and C amplify, since each loop returns to warmer air
   • A and C amplify; B damps, since it has one reversing link
   • B and C amplify, since each loop crosses three systems
   • A just amplifies, since water vapor is the one gas that traps heat

5. Card

   Trees supply 30% of a region's rain by releasing water vapor (example data). Loop: less rain removes trees, fewer trees release less vapor, and less rain falls.

6. 3.

   A drought removes 20% of the forest. Luz assumes vapor falls in step. By what percent does rain fall, and what sign is the loop?

   • Rain falls 30%; the loop is positive, since less rain removes more trees
   • Rain falls 6%; the loop is negative, since fewer trees need less rain
   • Rain falls 6%; the loop is positive, since less rain removes more trees
   • Rain falls 20%; the loop is positive, since less rain removes more trees

7. Summer sea ice and ocean warmth (example data)

   Year	Sea ice (million km2)	Ocean warming (degrees C)
   2000	6.3	0.2
   2010	4.9	0.5
   2020	3.7	0.8

8. 4.

   Jun judges four claims about the table. Which claim does it support best?

   • The table proves that ice loss caused all of the warming and nothing else did
   • The table proves that warming caused all of the ice loss and nothing else did
   • Ice and temperature moved in opposite years, so the two systems are unrelated
   • Ice fell 2.6 million km2 as the ocean warmed 0.6 degrees C, which fits an ice-albedo loop but does not prove it

9. A bay over 30 years (example data)

   Year	Nitrate load (thousand tonnes)	Lowest bottom oxygen (mg/L)
   1990	20	4.0
   2000	30	2.5
   2010	45	1.2
   2020	30	2.0

10. 5.

    Kira judges claims about the table. Which claim does it support best?

    • Oxygen fell as nitrate rose, then partly recovered: a link, not proof of one cause
    • The table shows that nitrate alone caused the low oxygen in this bay over 30 years
    • Cutting the load restored oxygen fully, back to its level in 1990
    • Low oxygen drove the nitrate load up, since the two moved together
11. 6.

    A pulse of methane halves every 8 years (example data) and mixes through the air within about a year. What remains after 24 years, and where, by Ren?

    • One eighth remains, spread through the whole atmosphere
    • One third remains, spread through the whole atmosphere
    • One sixth remains, spread through the whole atmosphere
    • One eighth remains, kept near the place it was released

12. Card

    Nitrate travels 2,000 km down a river at 0.5 m/s to a bay. The bay forms warm, layered water in early June.

13. 7.

    Fertilizer washes into the river on April 15. When does Tala expect the nitrate to reach the bay, and why does it matter?

    • About June 1, just as warm, layered water starts to trap low oxygen
    • About April 20, so the nitrate reaches the bay well before the bay layers
    • About June 1, but the nitrate stays on the farm and does not reach the bay
    • About July 2 of the next year, after the bay layers and mixes again

14. Feedback strengths (rounded textbook values)

    Feedback	Strength (W/m2 per degree C)
    More heat radiated to space	-3.2
    Water vapor	1.8
    Sea ice and snow	0.4

15. 8.

    Ari adds the strengths. Which feedbacks amplify warming, and what does the sum say?

    • Water vapor and sea ice and snow amplify; the sum is +2.2, so warming runs away
    • The three damp warming; the sum is -5.4 W/m2 per degree C, so Earth cools
    • Water vapor and sea ice and snow amplify; the sum is -1.0, so Earth settles
    • Heat radiated to space amplifies, since its number is the largest
16. 9.

    A, farmland around it, 80, 45, 0.8; B, forest around it, 10, 4, 7.5. Milo compares the lakes. Which interaction explains lake A's low oxygen?

    • Algae release oxygen, so lake A's 45 chlorophyll should raise its bottom oxygen
    • Lake B has less algae because it is deeper, as the table shows
    • Runoff phosphorus feeds algae, about 11 times the chlorophyll, and their decay uses up bottom oxygen
    • Low bottom oxygen made the algae grow, so the algae came second

17. How fast each feedback responds (approximate)

    Feedback	Time to respond
    Sea ice and snow	years to decades
    Permafrost carbon	decades to centuries
    Rock weathering	about 100,000 years

18. 10.

    Esme asks if rock weathering could cancel warming within 100 years. Which reply is best?

    • No: weathering acts on rocks, so it cannot change the air
    • No: weathering responds over about 100,000 years, about 1,000 times slower than 100 years
    • Yes: weathering is a negative loop, so it cancels warming at any speed
    • No: weathering responds about 100 times slower than 100 years