# Climate and Biomes

History I · Geography · https://tryals.app/learn/history-i/climate-and-biomes

## Climate, Not Weather

Weather is what happened on Tuesday. **Climate is the distribution weather is drawn from**: the averages and the variance. For history, the variance matters more than the mean because populations live at the level bad years permit.

Wladimir Köppen classified climate by **vegetation**, since plants integrate temperature and rainfall.

| Group | Name | Character |
|---|---|---|
| **A** | Tropical | Hot, wet; no real winter |
| **B** | Arid | Evaporation exceeds precipitation |
| **C** | Temperate | Mild winters |
| **D** | Continental | Cold winters, warm summers |
| **E** | Polar | No warm season |

**Arid** (Group B) means evaporation exceeds precipitation. This is a budget, not a thermometer reading, which is why cold deserts exist.

## Climate's Fingerprints

Paleoclimatology reads climate signatures: **tree rings** (growing season), **ice cores** (atmosphere), **pollen cores** (biomes), and **speleothems** (rainfall). These track events like the **Medieval Climate Anomaly** (c. 950–1250) and **Little Ice Age** (c. 1300–1850).

**Climate is a stressor, not a script.** The Norse abandoned Greenland during the Little Ice Age while the Inuit thrived under identical conditions:

same climate + different subsistence $\longrightarrow$ opposite outcomes

**The methodological trap is correlation.** A cold decade next to a revolt is a coincidence until you trace the mechanism through harvest yields, grain prices, and mortality.

## Practice questions

6 of this lesson's 11 practice questions, with answers. The full set is in the app.

### 1. Why can variance matter more than average rainfall for a historical population?

A. Variance affects only pastoral, not agricultural, societies
B. High-variance climates always receive less total rain
C. Averages are harder to measure in the historical record
D. Populations live at the level the bad years permit, not the average ones

**Answer:** D. Populations live at the level the bad years permit, not the average ones

**Why:** Two regions with identical average rainfall are not the same place if one delivers it reliably and the other does not. The bad year sets the ceiling, and everything above it is temporary.

Page: https://tryals.app/practice/history-i/climate-and-biomes/why-can-variance-matter-more-than-average-rainfall-for-a-historical

### 2. Two regions have identical mean rainfall; one supports dense settlement and the other does not. What is the likely difference?

A. Soil quality, which mean rainfall does not capture
B. Reliability: the bad years set the ceiling
C. Temperature, which determines the growing season independently of rainfall
D. The distribution of rainfall across the day, which affects absorption

**Answer:** B. Reliability: the bad years set the ceiling

**Why:** Famine is set by the worst years rather than the typical one, so variance is the binding constraint and the mean can mislead completely. Storage, irrigation and trade are all technologies for converting a variable supply into a reliable one, which is why they appear exactly where variance is high.

Page: https://tryals.app/practice/history-i/climate-and-biomes/two-regions-have-identical-mean-rainfall-one-supports-dense

### 3. Sort each proxy by what it directly records.

**Answer:**

- Records year-by-year growing conditions: Tree rings, Ring width in a drought-stressed oak
- Records atmosphere and volcanism: Trapped air bubbles in ice cores, Volcanic ash layers in an ice sheet
- Records vegetation and biome: Pollen cores, Shifting species ratios in a lake sediment

**Why:** Each proxy answers a different question at a different resolution, tree rings are annual and exactly dated, ice cores reach the atmosphere itself, pollen gives you the biome century by century.

Page: https://tryals.app/practice/history-i/climate-and-biomes/sort-each-proxy-by-what-it-directly-records

### 4. Put these climate episodes in chronological order.

**Answer:**

1. 536 CE dust veil dims the sun for over a year
2. Medieval Climate Anomaly begins (c. 950)
3. Norse settlement of Greenland flourishes
4. Little Ice Age sets in (c. 1300)
5. Seventeenth-century general crisis
6. Little Ice Age ends (c. 1850)

**Why:** The correlations are real and dramatic, which is exactly what makes them dangerous. Two dates lining up is a hypothesis, not a finding.

Page: https://tryals.app/practice/history-i/climate-and-biomes/put-these-climate-episodes-in-chronological-order

### 5. The Little Ice Age caused the abandonment of Norse Greenland.

**Answer:** False

**Why:** The Inuit lived through the identical climate in the identical place and did not leave. The cold was a stressor; the Norse commitment to a European farming package was the vulnerability, and that was a choice about identity, not a fact about the weather.

Page: https://tryals.app/practice/history-i/climate-and-biomes/the-little-ice-age-caused-the-abandonment-of-norse-greenland

### 6. What does "climate is a stressor, not a script" mean in practice?

A. Institutions, reserves, and choices determine what a stress does
B. The same climatic shift produces different outcomes in different societies
C. Climate has no measurable effect on historical events
D. Climate changes the difficulty setting rather than the result

**Answer:** A. Institutions, reserves, and choices determine what a stress does; B. The same climatic shift produces different outcomes in different societies; D. Climate changes the difficulty setting rather than the result

**Why:** The stress is real and it is not the author. The same Little Ice Age wrecked one polity and found another that traded, stored, or adapted its way through.

Page: https://tryals.app/practice/history-i/climate-and-biomes/what-does-climate-is-a-stressor-not-a-script-mean-in-practice