Estimating the CO₂ emissions associated with storing 100 MB of emails per year involves considering the energy consumption of data storage and the carbon intensity of that energy.

Here's a rough approximation:

1. **Energy used per GB of data stored per year:**
Data centers typically consume about 0.1 to 0.5 kWh per GB annually, depending on efficiency. Let's take an average of **0.2 kWh per GB per year**.

2. **Convert 100 MB to GB:**
100 MB = 0.1 GB

3. **Calculate energy consumption:**
0.1 GB × 0.2 kWh/GB = **0.02 kWh per year**

4. **Estimate CO₂ emissions:**
The carbon intensity of electricity varies globally.
- Average global carbon intensity: approximately **0.4 kg CO₂ per kWh** (this is a rough global average; it can be higher or lower depending on the energy mix).

5. **Calculate CO₂ emissions:**
0.02 kWh × 0.4 kg CO₂/kWh = **0.008 kg CO₂ per year**

**Approximate result:**
Storing 100 MB of emails for a year emits roughly **0.008 kg (8 grams) of CO₂**.

**Note:**
- This is a very rough estimate; actual emissions depend on data center efficiency, energy source, and hardware specifics.
- For larger data volumes or different storage practices, the emissions could scale proportionally.

**Summary:**
Storing 100 MB of emails for a year results in approximately **8 grams of CO₂ emissions**. chatGPT