**Core Concept**
The oxygen dissociation curve describes the relationship between the partial pressure of oxygen (pO2) and the oxygen saturation of hemoglobin in the blood. Shifts in the curve can affect the release of oxygen to tissues. Factors that shift the curve to the right facilitate the release of oxygen to tissues, whereas a left shift indicates a decrease in oxygen release.

**Why the Correct Answer is Right**
The Bohr effect describes how carbon dioxide (CO2) and hydrogen ions (H+) in the blood increase hemoglobin's affinity for oxygen, leading to a left shift in the oxygen dissociation curve. This is because CO2 and H+ ions bind to hemoglobin, reducing the release of oxygen to tissues. On the other hand, factors that increase CO2 and H+ ions in the blood or decrease pH will shift the curve to the left, not to the right.

**Why Each Wrong Option is Incorrect**
**Option A:** **2,3-Bisphosphoglycerate (2,3-BPG)** is a molecule produced by red blood cells that binds to hemoglobin, reducing its affinity for oxygen and shifting the oxygen dissociation curve to the right. This facilitates the release of oxygen to tissues.

**Option B:** **Temperature increase** also shifts the oxygen dissociation curve to the right, as higher temperatures increase the metabolic rate of tissues, leading to a greater demand for oxygen.

**Option C:** **Increased CO2 levels** will also shift the curve to the right, as increased CO2 levels lead to a decrease in pH, which in turn reduces hemoglobin's affinity for oxygen.

**Clinical Pearl / High-Yield Fact**
Remember that factors that increase CO2 and H+ ions in the blood (such as increased metabolic rate, fever, or respiratory acidosis) will shift the oxygen dissociation curve to the right, facilitating oxygen release to tissues.

**Correct Answer:** D. The Bohr effect, which involves CO2 and H+ ions, shifts the oxygen dissociation curve to the left, not to the right.